KENYA STANDARD      2791  :2018  
ICS 85.080.01  
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Painting of buildings — Code of 
practice  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
© KEBS 201 8 Edition , 2018 
 
 
  2791  :2018  
 
ii  © KEBS 2018 — All rights reserved  TECHNICAL COMMITTEE REPRES ENTATION  
 
The following organizations were represented on the Technical Committee:  
 
 
 
 
 
Kenya Bureau of Standards — Secretariat  
 
 
 
 
REVISION OF KENYA STANDARDS  
 
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for improvements to published standards, addressed to the Managing Director, Kenya Bureau of Standards, 
are welcome.  
 
 
 
 
 
 
 
© Kenya Bureau of Standards, 201 8 
 
Copyright. Users are reminded that by virtue of Section 25 of the Copyright Act, Cap. 130 of 2001  of the Laws of Kenya, copyright 
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  KENYA STANDARD                                                2791  :2018  
ICS 85.080.01  
© KEBS 2018 — All rights reserved    iii  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Painting of buildings — Code of practice  
 
 
 
 
 
 
 
 
 
 
 
 
 
KENYA BUREAU OF STANDARDS (KEBS)  
 
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  2791  :2018  
 
iv  © KEBS 2018 — All rights reserved   
Foreword  
 
This Kenya Standard was prepared by the                  Technical Committee under the guidance of the 
Standards Projects Committee, and it is in accordance with the procedures of the Kenya Bureau of 
Standards . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
KENYA STANDARD               KS 2791  :2018  
 
 
© KEBS 2018 — All rights reserved    1  
Painting of buildings — Code of practice  
 
 
 
 
1 Scope  and field of application  
 
1.1 This Kenya Standard  gives recommendations for good practice in initial painting and maintenance 
painting of buildings internally and externally, e.g. dwellings, offices, light industrial buildings, schools, 
hospitals, hotels and public buildings generally, in which decoratio n is a significant and often the major 
factor. The code takes into account the need to protect many building materials against the weather or other 
forms of attack normally encountered.  
 
NOTE 1  Further guidance on the protection of steel structures, is giv en in ISO 12944.  
 
1.2 The coatings referred to in this code are principally of conventional type, as defined in A.2, but 
limited reference is made to specialist coatings (A.3) and factory -applied coatings (A.4). In respect of 
materials generally, the code  does not cover in detail the wide and constantly increasing range available. 
Some materials have been excluded because of their obsolescence, limited or specialized usage or, in the 
case of newly -developed products, lack of experience of their performance  in service.  
 
NOTE 2  Product references are indicated in the text by figures in parentheses, e.g. (3/2), and refer to the products listed and desc ribed 
in Table 3 to Table 11.  
 
1.3 The code does not cover:  
 
a) decorative processes and other work usually ca rried out by specialists;  
 
b) the particular requirements of listed or historic buildings  
 
NOTE 3   Buildings which are listed or which lie within a conservation area are protected by law. This does not mean that you can neve r 
alter or demolish one, but c arrying out relevant work without the appropriate consent is a criminal offence.  
 
c) lime wash and distemper coatings;  
 
d) preservative treatments for structural timber;  
 
e) coatings for fire protection; and  
 
f) general safety hazards of access for paint ing (Annex C).  
 
The recommendations made in the code are intended to facilitate achievement of standards of finish likely to 
be acceptable in most cases in the types of buildings, providing that the work of other t rades has been 
completed to a satisfactory  standard.  Where especially high standards of finish are necessary, more 
elaborate processes and systems than those described in the code might be necessary and should be 
specified accordingly.  
 
2 Normative references  
 
The following referenced documents are indispensable for the application of this standard. For dated 
references, only the edition cited applies. For undated references, the latest edition of the referenced 
document (including any amendments) applies.  
 
BS 476 (all parts), Fire tests on build ing materials and structures  
 
BS 1070, Specification for black paint (tar -based)   
2  © KEBS 2018 — All rights reserved   
BS 1191 -1, Specification for gypsum building plasters — Part 1: Excluding premixed lightweight plasters  
 
BS 1191 -2, Specification for gypsum building plasters — Part 2: Premi xed lightweight plasters  
 
BS 1336, Specification for knotting  
 
BS 2015, Glossary of paint and related terms  
 
BS 2992, Specification for painters' and decorators' brushes for local authorities and public institutions  
(excluding quality of fillings)  
 
BS 3416 , Specification for bitumen -based coatings for cold application, suitable for use in contact with 
potable water  
 
BS 3761, Specification for solvent -based paint remover  
 
BS 3900 (all parts), Methods of test for paints  
 
BS 4072, Copper/chromium/arsenic preparations for wood preservation  
 
BS 4652, Specification for zinc -rich priming paint (organic media)  
 
BS 4756, Specification for ready -mixed aluminium priming paints for woodwork  
 
BS 4764, Specification for powder cement paints  
 
BS 5262, Code of practice  for external renderings  
 
BS 5493, Code of practice for protective coating of iron and steel structures against corrosion  
 
BS 5589, Code of practice for preservation of timber  
 
BS 5707, Specification for preparations of wood preservatives in organic solven ts 
 
BS 6949, Specification for bitumen -based coatings for cold application excluding use in contact with potable 
water  
 
BS 7079 -A3, Preparation of steel substrates before application of paints and related products — Visual 
assessment of surface cleanliness  — Part A3: Preparation grades of welds, cut edges and other areas with 
surface imperfections  
 
BS 7664, Specification for undercoat and finishing paints  
 
BS 7956, Specification for primers for woodwork  
 
BS 8000 -12, Workmanship on building sites — Part 12: Code of practice for decorative wall coverings and 
painting  
 
BS 8221 -1, Code of practice for cleaning and surface repair of buildings — Part 1: Cleaning of natural 
stones, brick, terracotta and concrete  
 
BS 8417, Preservation of timber — Recommendations  
 
BS EN 350 -2, Durability of wood and wood -based products — Natural durability of solid wood — Part 
2: Guide to natural durability and treatability of selected wood species of importance in Europe  
 
BS EN 927 -1:1997, Paints and varnishes — Coating materials a nd coating systems for exterior wood  
— Part 1: Classification and selection  
 
BS EN 971 -1, Paints and varnishes — Terms and definitions for coating materials — General terms  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    3  
BS EN 12811 -1, Temporary works equipment — Scaffolds — Part 1: Performance require ments and general 
design  
 
BS EN ISO 2409, Paints and varnishes — Cross -cut test  
 
BS EN ISO 4624, Paints and varnishes — Pull off test for adhesion  
 
BS EN ISO 12944 (all parts), Paints and varnishes — Corrosion protection of steel structures by protective 
paint systems  
 
DD ENV 927 -2, Paints and varnishes — Coating materials and coating systems for exterior wood — Part 2: 
Performance specification  
 
3 Terms and definition s 
 
For the purposes of this Kenya Standard, the terms and definitions given in (Insert equ ivalent ISO), and the 
following apply.  
 
3.1  
thixotropy  
property  of  changing  reversibly  from  a  gel  or  semi -liquid state  when  at  rest  to  a  more  liquid 
consistency when shearing forces are applied at a constant rate over a period of time  
 
NOTE  Shearing forces include for example brushing or stirring.  
 
3.2  
flow 
extent to which a coating is able to flow out to a film of uniform thickness free from brush marks and similar 
irregularities produced by the method of application  
 
3.3  
undercoat  
relati vely highly pigmented matt or mid sheen materials, applied to primed or previously painted surfaces 
before the application of finishing coats  
 
3.4 
ancillary materials  
materials other than coatings used in the painting of buildings  
 
NOTE  Ancillary materials  include for example cleaning agents, sterilizing washes, knotting, stoppers and fillers, mastics, paint 
removers and waterproofing treatments.  
 
4 Design considerations  
 
4.1 General  
 
Many modern building materials do not require painting. If, however, building materials are chosen which 
require painting for aesthetic or protective reasons, then design factors should be considered by the architect 
at the earliest possible stage. Specifiers need to consider design aspects from the perspective of coating 
selection, maintenance and expected service life. Opportunities for design change after construction are very 
limited. For some new build components, e.g. window frames, initial painting is best carried out industrially 
prior to installation.  
 
Correct selec tion of coating systems and clear, precise specifying of methods and processes are essential. 
However, this alone does not ensure that the chosen systems perform satisfactorily, and it is equally 
important that consideration be given to the factors describ ed in Table 1. Of particular importance in relation 
to performances is the influence of design and detailing, proper organization and supervision and, in some 
circumstances, an effective inspection procedure. Exposure conditions are the consequence of cons truction 
and climatic factors (e.g. Table 2). The guidance on typical life to maintenance will be system specific and  
4  © KEBS 2018 — All rights reserved  apply to mild and moderate exposure conditions as  described  in  Table  2.  Service life will be  shorter  
under  more  severe conditions . 
 
Hazards to health and safety that might be encountered in the painting of buildings and the precautions that 
need to be taken are described in Annex B. Reference is also made to applicable legislation (see also Annex 
B). These aspects should be consider ed in terms of a safe system of work. The health and safety of all 
persons involved in the building during the painting process, including client, occupier, painter, supervisory 
and inspection staff needs to be ensured.  
 
All parts of a building to which coatings are to be applied should be designed to avoid, as far as possible, the 
creation of features or conditions that can cause difficulties in application, impair the performance of coatings 
or promote decay or corrosion of structural materials.  
 
4.2 Accessibility  
 
Spaces between adjacent wood or metal members, e.g. in roof trusses, should be sufficiently wide to allow 
access for painting. Alternatively, hidden or contact surfaces should receive protective treatment before 
assembly or erection. Pipes and  similar components should be fixed sufficiently clear of walls to allow them 
to be painted completely.  
 
Access for external repainting should be considered at the design stage. Where necessary, scaffolding 
should be provided  
 
NOTE  The need for scaffoldin g for initial or maintenance painting will add considerably to the costs.  
 
4.3 Control of moisture  
 
Penetration of moisture is a common cause of the premature failure of coatings; it could also lead to 
biological decay or corrosion of structural materials.  Attention should be paid to the design and location of 
damp -proof courses and membranes, vapour barriers, flashings, weatherings, drip - mouldings and 
throatings. Measures should be taken to prevent the retention of water on horizontal surfaces, e.g. by 
bevelling or sloping them or, in the case of structural metalwork, by providing drainage holes. Rainwater run -
off or dripping on to coated surfaces should be prevented by appropriate detailing (see also C.2.6 and 8.3.3).  
 
NOTE  Condensation is likely to occur  in most buildings both externally and internally. External condensation (i.e. dew) will in 
combination with rainfall contribute to the overall time of wetness with detrimental effects on durability. Internally persis tent condensation 
can cause failure of coatings both physically and through biological attack. The latter includes surface moulds and in the case of 
interstitial condensation an increased risk of decay.  
 
Measures to prevent or minimize condensation should be incorporated at the design stage but  choice of 
coating can also make a contribution (see 4.6.4.2 and 4.6.4.3).  
 
4.4 Profiles  
 
Coatings have a tendency to recede from sharp edges during application and this could result in the film 
having inadequate thickness at these points. Timber arrises s hould be slightly rounded, a radius of 1 mm to 
2 mm for timber other than sills and thresholds usually being sufficient: sills and thresholds might need a 3 
mm rounding. Sharp edges of metal, e.g. burrs and nibs, should be removed before painting.  
 
4.5 Selection of materials  
 
4.5.1  General  
 
Materials used in the painting of buildings can be divided into three main categories:  
 
a) pigmented coatings, e.g. primers, undercoats, paints and wood stains;  
 
b) unpigmented coatings, e.g. varnishes;  
 
c) ancillary materials,  e.g.  fillers,  stoppers  and  materials  similarly  used  in  the  preparation of 
surfaces or in coating systems.  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    5  
Materials should be selected from Tables 3 to Table 11 in accordance with 7.1 to 7.3 for coatings and in 
accordance with 7.4 for  ancillary materials.  
 
4.5.2  Volatile organic compounds  
 
When selecting coatings, the volatile organic compound (VOC) content of coatings and its effect on the 
environment should be taken into account.  
 
4.6 Selection of coating systems  
 
4.6.1  General  
 
A nu mber of factors should be considered when selecting coating systems. Selection is often be made on a 
qualitative basis, judging the relative importance of the factors in relation to particular circumstances. If more 
than one type of system meets the specif ication, then selection might be made on the basis of relative cost, 
availability or individual preference.  
 
NOTE 1  Care should be taken to ensure that factors are comparable; lower initial costs might well be more than outweighed by shorter  
life and conse quent higher maintenance expenditure. In other circumstances, a single factor might exert so strong an influence that 
selection is limited to a single type of system.  
 
Factors, which should be considered when selecting coating systems, are listed in Table 1. There is a 
considerable degree of interaction between factors involved, and they should not be considered in isolation. 
The selection of coating systems and their suitability for substrates or groups of substrates should be 
determined using Tables 12 to  18. 
 
NOTE 2  Information is given in the relevant tables on the expected life to first maintenance in mild or moderate exposure conditions , 
which have been categorized in Table 2.  
 
Possible paintwork defects that might be encountered and the recommended re medial treatment for these 
should be determined using Table 19 and Table 20.  
 
4.6.2  Exposure conditions  
 
General and local exposure conditions and the conditions of service are major factors in the selection of 
coating systems. Reference should be made to 4.6.4 for information on special conditions that could 
influence selection.  
 
NOTE  A broad distinction can be made between external and internal exposure conditions but, in either, there can be considerable 
variation in the severity of attack or rigours of service, even within a single building. Externally, the main variables are location, proximity 
to the coast and level and nature of atmospheric pollution but elevation, aspect and the direction of prevailing winds can al so have a 
significant effect. Intern ally, high humidity and the presence of process chemicals and dust can create severe conditions.  
 
Table 2 indicates the broad categories of external and internal exposure conditions that might be 
encountered and illustrates factors that should be considere d. It is intended to provide general guidance; it is 
not possible to take into account the many local variables that can influence the nature of the exposure 
conditions and the selection of coating systems in specific circumstances.  
 
4.6.3  Substrates and coating systems  
 
The properties of substrates and their influence on the selection of coating systems should be considered at 
the design stage (see Clause 8).  
 
NOTE 1  For new build there are dominant economic and operational factors for the choice of subst rates and methods of construction.  
Coatings may be required for aesthetic and/or protective reasons b ut cannot be expected to upgrade the performance of incorrectly 
specified building materials. The nature of the substrate will have a major impact on the suitability of specific coating systems.  
 
Building materials to which coatings are to be applied should be chosen for their inherent properties of 
durability and resistance to decay or corrosion in the exposure conditions in which they are to be used. Over -
reliance should not be placed on the ability of coatings to upgrade the performance of inherently unsuitable  
6  © KEBS 2018 — All rights reserved  materials, especially in circumstances where frequent maintenance is likely to be impracticable or 
uneconomic.  
 
Alternative or supplementary treat ments, e.g. galvanizing or sprayed metallic coatings (see 8.4.1.2), are 
available, as are ancillary treatments such as wood preservatives (see 8.1.5), to enhance the protection 
afforded by coatings.  
 
NOTE 2  Where possible it is advantageous to undertake in itial painting under controlled conditions, e.g. factory. This is often more 
satisfactory than site application and can offer a wider choice of systems.  
 
4.6.4  Special conditions and requirements  
 
4.6.4.1  General  
 
Because of the diversity of conditions, s ubstrates and coatings, especially in relation to chemical resistance, 
it is possible to provide only a general indication of the types of coatings that might be suitable. For detailed 
recommendations in specific circumstances, specialist advice should be sought.  
 
4.6.4.2  High humidity  
 
Most paints are resistant to the levels of humidity normally encountered internally in most domestic and non -
industrial situations. Where conditions of moderate or high humidity prevail intermittently, as in kitchens and 
bathrooms, only resistant coatings should be used.  
 
NOTE 1  This will include most solvent -borne paints and some water -borne paints (7/1, 7/2, 7/3 and 7/4).  
 
The processes or activities carried out in some buildings can give rise to conditions of constant o r frequent 
high humidity or cause surfaces to be splashed with water. (Examples where such conditions might prevail 
include swimming baths, laundries and factories engaged in the manufacture of food and drink,  paper  and  
synthetic  and  natural  fibres.)  In these  conditions, and  especially for  the protection of steel, wood and 
other substrates vulnerable to attack by moisture, specifically moisture - resistant coatings should be used.  
 
Acrylated rubber paints (11/5), especially high -build types, have go od moisture resistance and are available 
in a wide range of colours. Where colour is not important, bituminous coatings (see Table 10), including coal 
tar epoxies, can be used. Bituminous coatings can be used to provide semi -drying protective coatings with  
good moisture resistance which are suitable for use on surfaces not subject to handling or abrasion.  
 
Moisture -resist ant protective coatings should be applied in accordance with the manufacturer's 
recommendations in regard to thickness, preparation and pr iming.  
 
NOTE 2  Many moisture -resistant protective coatings need to be applied at a thickness of 100 mm or more  
 
4.6.4.3  Condensation  
 
Condensation should be prevented or controlled by providing good ventilation to remove moisture - laden air 
from buildings, preferably from a point near the source of moisture. Adequate levels of heating increases the  
capacity of  the  air  to  hold  moisture but  should  be  combined with  good ventilation, otherwise the 
problem is aggravated. Thermal insulation al so helps to reduce condensation by keeping surfaces warmer 
and reducing the cost of heating.  
 
NOTE 3   Most condensation in buildings is caused by warm, moist air coming in contact with cooler surfaces. In domestic and non -
industrial buildings, condensation  is usually light and intermittent although, in some situations, it can be sufficient to cause water runs 
and drips, disfigure paintwork or promote mould growth. In dwellings, condensation is most likely to occur in kitchens and ba throoms, 
but water vapour  can be carried by air currents through the house from these rooms and condense on cold surfaces in unheated areas  
 
Paint treatment alone should not be used as an alternative to heating, ventilation and thermal insulation  
measures  but,  where  condensati on is  moderate  and  occurs  only  intermittently,  anti - condensation 
paints can be used. They usually contain aggregates with insulating or absorptive properties. Some coatings 
have a textured surface that helps to reduce water runs and drips, but these  tend to hold dirt and are not 
easily cleaned. Absorptive types should be used only in situations where it is to be expected that 
condensation will be followed by conditions favourable to drying out of absorbed moisture.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    7 Where the function of a building g ives rise to conditions of constant or frequent high humidity and the 
measures to prevent or reduce condensation in the preceding paragraphs are impracticable or not fully 
effective, priority should be given to the protection of substrates vulnerable to mo isture attack by using 
specifically moisture -resistant coatings, as described in 4.6.4.2.  
 
4.6.4.4  Mould growth  
 
NOTE  Typically, mould has a black, sooty appearance and might be mistaken for dirt although some moulds are coloured. It is often 
possible to  distinguish mould from dirt and chemical stains by examination with a magnifying glass (X10 or higher) when the filaments or 
hyphae characteristic of most moulds might be seen.  
 
Moulds germinate and grow when the relative humidity at a surface rises above  80% and where there is a 
supply of nutrients. Mould growth should be avoided by:  
 
a) ensuring the relative humidity does not exceed 70%. Because of its dependence upon a supply of 
moisture, the growth of mould is most effectively inhibited by reducing humidity and preventing condensation 
by good ventilation, adequate heating and thermal insulation, as indicated in 4.6.4.3; or  
 
b) applying  moisture -resistant  protective  coating  (see  4.6.4.2)  and  sterilizing  the  surface  by 
application of a fungic idal wash at regular intervals. Proprietary washes containing fungicides are available, 
and some leave an inhibitive residue on the surface; a solution of household bleach also kills mould but does 
not have any residual inhibitive properties; or  
 
c) applyi ng mould -resistant paints in domestic and non -industrial situations. When mould -resistant 
paints or washes are to be used where foodstuffs are prepared or stored, it should be ensured that there is 
no risk of food products being contaminated with toxic sub stances or their flavours affected. Mould -infected, 
previously decorated internal surfaces before painting, should be treated in accordance with 11.5.8.  
 
NOTE 5  Mould -resistant paints usually contain mould -inhibitive additives.  
 
Some more toxic mould -inhib itive additives might not be suitable for use in situations where foodstuffs are 
processed.  
 
4.6.4.5  Chemical attack  
 
Coatings are likely to be attacked chemically by high concentrations of acids and alkalis, acidic and alkaline 
substances, alcohols, oils , fats and greases, solvents and fresh and salt water.  
 
In mildly acidic industrial exposure conditions, alkyd gloss and drying -oil/resin micaceous iron oxide paints 
can be used and should be applied to prepared and primed surfaces in systems of adequate t hickness to 
achieve a defect -free film. Where there is a need for resistance to heavy fume attack or direct contact with 
chemicals, chemical -resistant coatings should be used.  
 
NOTE   Chemical -resistant  coatings  include  acrylated  rubber,  two -pack  epoxy  and  polyurethane,  coal -tar  epoxy  and 
bituminous types (see Table 10 and Table 11).  
 
The resistance of any of the coatings described in Table 11 is dependent on the specific agent and the form 
and severity of attack. When there appears to be a ne ed for a chemical -resistant coating, specialist  advice  
should  be  sought  unless  there  is  previous  experience  of  the  satisfactory performance of a particular 
type of coating in similar circumstances.  
 
4.6.4.6  Fire 
 
For further information on fire , see Annex D.  
 
4.6.4.6.1 Painted surfaces  
 
A painted surface should be considered as a thin film of flammable material in close contact with a substrate. 
The potential for the release of flammable volatiles (and therefore for a fire to occur) is a functio n of the 
nature of the paint film itself and the nature of the substrate. Paints would not normally affect the flame -
spread rating of the unpainted surfaces( see 4.6.4.6.2.)   
8  © KEBS 2018 — All rights reserved   
4.6.4.6.2  Resistance to surface spread of flame  
 
NOTE        Attention is drawn to the Building Regulations which require that, in certain types of buildings, the materials of which wall s 
and ceilings are constructed conform to specified minimum requirements in relation to the spread of flame across the surfac es. 
 
Paints should either be of conventional type conforming to specified minimum requirements in relation to the 
spread of flame across the surfaces. Flame -retardant paints can be conventional paints containing flame - 
retardant additives or types that int umesce (swell on heating). They should be applied as recommended by 
the manufacturer. The flame spread rating of paint cannot be expressed in isolation but only in relation to its 
performance on a specified substrate. Reference should be made to the manufa cturer's details of the ratings 
of their paints when applied to specified substrates.  
 
The flame spread rating of a painted surface can worsen with increasing film thickness or in situations where 
conventional paints are applied over flame -retardant types.  In the latter event, compatibility problems can 
also arise. To avoid such difficulties, details of systems applied, including dates of application and types or 
brands of paints used, should be recorded for future reference. It can also be helpful to label  surfaces to 
which flame -retardant paints have been applied.  
 
NOTE  Where Building Regulations require the materials of which walls or ceilings are constructed to have a specified flame - spread 
rating, flame -retardant paints applied on site cannot be used t o upgrade materials that do not meet Building Regulation requirements.  
 
4.6.4.7  Resistance to abrasion  
 
NOTE  Coatings resistant to abrasion might be required for floors, machine surfaces, storage racks and bins, handrails and similar 
items, especially in  factories and commercial buildings. There might also be a need for watt and ceiling finishes to be resistant to 
frequent vigorous cleaning in such places as dairies, abattoirs and food preparation areas.  
 
Pigmented and clear two -pack epoxy and polyurethan e coatings should be used where resistance to 
abrasion is a major consideration, but their use might be limited by the nature of the substrate or the 
conditions of application.  
 
NOTE  The modified one -pack types, although lower in abrasion resistance, can a lso be used, as they are subject to fewer 
restrictions in use and perform reasonably well in many situations; one -pack epoxy ester types, for example, can be used as floor and 
deck paints, often with a non -slip additive. Some modified alkyd paints are reas onably resistant to abrasion and can be used for painting 
machinery and similar applications. Multi -colour finishes (7/14) can be used for walls in many interior hard wear situations.  
 
4.6.4.8   Anti-graffiti treatments  
 
Paint graffiti is an increasing prob lem in buildings and any organization with buildings that are vulnerable to 
attack should have a policy on removal or protection. New or undamaged surfaces should be assessed for 
the likely risk and cost of countermeasures. Choices for the prevention inclu de sacrificial, semi -permanent 
and permanent coatings (see E.3.1).  
 
Where graffiti is already a problem, measures of removal or obliteration should be assessed taking into 
account any hazards to the public during removal operations. Physical and chemical m ethods are available 
but the choice of method will depend on the nature of the marker and the substrate. Specialist manufacturers 
should be consulted and preliminary testing carried out on small areas (see E.1 and E.2).  
 
NOTE  For further information on ant i-graffiti treatments, see Annex E.  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    9 Table 1 — Selection of coating systems  
 
Issue  Question  Action  
Exposure conditions  What is the general atmospheric 
exposure conditions, external and 
internal?  Consider location and functions of buildings  
What localized or intermittent conditions 
(e.g. fumes, condensation, heat, 
vulnerability to abrasion or wear) exist 
or are to be expected?  Refer to 7.1, Table 2 and 4.6.4. Consider  
possible future developments or changes in  
usage, which might alter the local ex posure  
conditions  
Function  What are the functional requirements 
(e.g. of protection, decoration, hygiene 
or special function)?  Refer to 7.1 and 4.6.4. Design remit and 
experience. Consider substrate. Consider  
exposure conditions (see 4.6.2)  
Are there any relevant statutory 
requirements (e.g. under the Building 
Regulations or Factories Act) affecting 
selection?  Relevant legislation (see also Annex B)  
Substrate  What substrates are involved?  Design, remit, specification or inspection  
Do their characteristics influence the 
selection of coating systems?  Refer to 8.1 to 8. 15  
Special constraints 
on selection  Are there constraints relating to the 
composition of the coatings in some 
situations (e.g. in food factories 
because of the risk of toxicity  or 
tainting)?  Consult client, industry association or supplier  
Are the materials chosen to minimize 
solvent content and the systems of 
working specified compliant with 
legislation?  Refer to Clause 10 and Annex B  
Are any constraints imposed by the 
conditions under which the work has to 
be carried out (e.g. requiring the use of 
coatings which dry very quickly)?  Consult client, contractor or supplier. Refer to  
9.1 
Are there constraints imposed on colour 
choice by reason of solar gam?  Refer to 8.1.4.2  
Does the condition of the substrate (e.g. 
its high moisture content) impose 
constraints on the selection?  Ascertain condition, expected or actual, at time 
of treatment. Refer to 8.1 to 8.15  
Coatings  Which coating systems are available?  Consider  answers to preceding questions.  
Refer to Tables 3 to 11 and 8.1 to 8.15.  
Consult suppliers  
Are the coatings readily available from 
the usual sources or is special order or 
manufacture required?  Consult suppliers  
Are the coatings suitable for site or 
factory application?  Consult suppliers  
Are there any restrictions on methods of 
application on site?  Consult suppliers. Refer to Clause 9 for  
information on application methods   
10  © KEBS 2018 — All rights reserved  Issue  Question  Action  
Is application by specialist contractors 
required?  Consult supplier. Refer to Tables 3 to 11  
Has the environmental impact of the 
chosen system been considered?  Consult supplier. Refer to Tables 3 to 11  
Cost and 
Maintenance  What is the likely first cost of the 
system, including preparation, materials 
and application?  Cost analysis of previous work of a similar 
nature. Consult contractors and suppliers  
What is the expected life of the system 
to first maintenance?  Experience of similar systems. Refer to Tables  
12 to 17  
Does the system provide a satisfactory 
base for maintenance type perhaps with 
coatings of different type?  See 11.3  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    11  
Table 2 — Exposure condition categories  
 
Severity of 
Exposure  Corrosivity  
category (see 
ISO 
12944 -2) ( To 
be adopted)  Exterior  Other exterior  
factors  Interior  Other interior  
factors  
Mild C1 (very low)  - - Heated buildings  
with clean  
atmospheres, e.g.  
offices, shops,  
schools, hotels 
and 
domestic 
situations  Light soiling,  
abrasion or  
handling of 
surfaces  
C2 (low)  Inland areas 
(more  
than 10 km from 
the 
coast), 
nonindustrial  
with low  
levels of 
pollution  
and average 
rainfall  - Unheated 
buildings  
where 
condensation  
might occur, e.g.  
depots, sports  
halls  
Moderate  C3 (medium)  Urban and 
industrial  
atmospheres,  
moderate sulfur 
dioxide 
pollution.  
Coastal areas 
with 
low salinity  - More frequent  
moderate  
condensation, 
e.g. 
in kitchens, 
bathrooms, 
washrooms etc.  
Production rooms  
with high humidity  
and some air  
pollution, e.g. 
food processing  
plants,  
laundries,  
breweries, dairies  Moderate  
soiling, abrasion  
and handling of  
surfaces  
Severe  C4(high)  Industrial areas 
and 
coastal areas 
with moderate 
salinity.  
Coastal ship - 
and 
boatyards  Areas with a 
driving rain 
index of 7 or 
more)  
Find equivalent 
Standard)  Exposure 
conditions  
subject to 
frequent  
high humidity or  
heavy  
condensation,  
especially if 
pollutants, e.g.  
sulfur dioxide or Exposure  
conditions in  
which heavy  
soiling or  
hygiene  
requirements  
necessitate  
frequent  
cleaning of 
surfaces.   
12  © KEBS 2018 — All rights reserved  Severity of 
Exposure  Corrosivity  
category (see 
ISO 
12944 -2) ( To 
be adopted)  Exterior  Other exterior  
factors  Interior  Other interior  
factors  
ammonia, are 
present. Chemical  
plants, swimming  
pools  Surfaces 
subject  
to heavy  
abrasion or  
impact  
Very severe  C5-I (very high  
industrial)  
C5-M (very high  
marine)  Industrial areas 
with high 
humidity and 
aggressive 
atmosphere  
Coastal and 
offshore areas 
with high salinity  - Buildings or areas  
with almost  
permanent  
condensation and  
with high pollution  Surfaces in 
contact with  
chemicals,  
chemical  
solutions,  
process liquors  
and other  
aggressive  
agents  
NOTE For wood, the exposure conditions are better classified in accordance with BS EN 927 -1, which takes into account the 
construction and the climate. (NWI proposal)  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    13  
Table 3 — Primers for wood  
 
Ref. Description  General composition  Characteristics and usage  
3/1 Opaque primer  Pigmented primer, solvent -borne  
(typically alkyd) or water -borne  
(typically vinyl acetate or  
acrylic), for general use under  
paints  Primers of this type are suitable 
for 
general use on wood, fibre 
boards  
and chipboards  
3/2 Opaque primers  
conforming to BS 7956,  
Type AA) (NWI proposal)  Solvent -borne (typically alkyd) or  
water -borne (typically acrylic)  
pigmented primers of 3/1, but  
formulated for improved exterior  
durability  General purpose  
3/3 Semi -transparent  
primers conforming to  
BS 7956, Type BA) NWI 
PROPOSAL)  Solvent - or water -borne as 3/2  
using transparent pigments  Semi -transparent dual -purpose 
primers designed for over 
coating with either stain finishes 
or paints.  
Often used as the factory -applied 
primer for joinery. They are 
generally of lower durability than 
3/2 
primers and should be over 
coated with minimum delay  
3/4 Opaque primers  
conforming to BS 7956,  
Type CA)  Solvent -borne or water -borne  
primers as 3/2 with stain blocking  
properties  Primers that can be used directly 
over knots, resinous timbers and  
timbers pretreated with  
preservatives, such as metallic 
naphthenates, known to 
discolour  
subsequently applied paint films  
3/5 Ready -mixed  
aluminium primers  
conforming to BS 4756 (NWI 
proposal)  Solvent -borne drying -oil/resin  
type binder with aluminium  
pigment  An alternative to conventional  
solvent -borne wood primer more  
suitable for woods that are 
resinous  
or have  been treated with copper 
naphthenate wood preservative 
or creosote. Relatively 
impermeable to moisture. 
Application of an  
additional coat of 
undercoat/finish  
might be required to obliterate 
grey 
primer colour  
3/6 Preservative primers  Unpigmented or light ly 
pigmented solution of resins and  
fungicides in water or organic  
solvent  First coat of some proprietary 
wood  
coating systems, intended to 
seal 
porous and weather exposed  
surfaces and inhibit fungal 
colonization. Beneficial for  
14  © KEBS 2018 — All rights reserved  Ref. Description  General composition  Characteristics and usage  
treating  
weathered wood surfaces after  
mechanical preparation  
 
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    15 Table 4 — Primers for metal  
 
Ref. Description  General composition  Characteristics and usage  
4/1 Pretreatment,  
wash or etching  
primer, two -pack  Typically, polyvinyl butyral resin  
solution with phosphoric acid (as  
separate component) and a  
pigment (chromate containing  
primers now largely superseded  
by chromate -free primers)  The main function of these 
primers is to improve adhesion of 
paint systems to non -ferrous 
metals.  
They can also be used to provide 
temporary  
protection to blast -cleaned steel 
and sprayed metallic coatings. 
The two -pack types generally give 
superior performance but might 
be less convenient to use. 
Application of primers of this type 
does not usually obviate the need 
for the application of a norm al 
type of primer subsequently. Most 
pre-treatment  
primers can be used in 
conjunction with  
conventional and specialist 
coating systems  4/2 Pretreament, wash or etching 
primer, one pack.  Typically, polyvinyl  
butyral/phenolic resin solution  
with tinting pigment  
4/3 Mordant solution  Water -borne pre -treatment for  
galvanized and non -ferrous  
metals  Contains an indicator which 
darkens the surface of  
galvanized steel indicating that it 
has reacted  
4/4 Adhesion  
promoter  Water -borne pre -treatment for  
non-ferrous metals and stainless  
steel  Pretreatment with low VOC 
content designed to  
improve adhesion of subsequent 
coating system to  
non-ferrous metals and stainless 
steel  
4/5 Zinc phosphate  
primer (see also  
4/8 and 5/4)  Solvent -borne. Typically, drying 
oil/ resin type binder with zinc 
phosphate as the main inhibitive 
pigment. Other tinting pigments  
can be incorporated  Zinc phosphate offers advantages 
over other inhibitive pigments in 
being less toxic and neutral in 
colour. Zinc phosphate primers 
are fair ly quick drying and can 
afford protection without finishing 
coats for reasonable periods. 
Established usage is  
for priming steelwork, but some 
types might be  
suitable for non -ferrous metals; 
refer to  
manufacturer’s recommendations  
4/6 Chromate primer  
(limited  
availability) for  
specialist use  Solvent -borne. Typically, drying 
oil/ 
resin type binder with zinc 
chromate as the main inhibitive 
pigment. Red oxide or other  
pigments can be incorporated  Vary according to formulation, but 
chromate primers  
are usu ally fairly quick -drying and 
suitable for use  
on ferrous and non -ferrous metals   
16  © KEBS 2018 — All rights reserved  Ref. Description  General composition  Characteristics and usage  
4/7 Zinc-rich Primer A)  
conforming to BS  
4652 (two -pack), (NWI 
proposal)  
solvent -borne  Solvent -borne. Based on epoxy  
resin and supplied in two -pack  
form (zinc paste and curing  
agent)  A quick -drying metallic -grey 
primer for iron and steel with rust -
inhibiting properties. Apply to well -
prepared (e.g. blast -cleaned) steel 
only. Often used  
for touching up damaged zinc 
coatings, e.g. zinc sprayed  
or galvanized surfaces or as a 
prefabrication primer. Spray 
application is  
recommended, except on small 
areas  
4/8 Zinc-rich primer  
(one-pack)  Solvent -borne. Based on a 
nonsaponifiable  
medium, e.g.  
chlorinated rubber  A quick -drying metallic -grey 
primer for iron and steel with rust-
inhibiting properties. Often used 
for 
touching up damaged zinc 
coatings, e.g. zinc sprayed  
or galvanized surfaces  
4/9 Zinc phosphate  
primer, waterborne  Water -borne. Based on an acrylic  
resin dispersion in water and  
typically containing a zinc  
phosphate anticorrosive pigment  A quick -drying primer for iron and 
steel as well as non -ferrous 
metals including galvanizing. 
Some  
versions described as universal 
primer (5/4) and  
can be used on timber surfaces  
4/10 Two pack epoxy primer  Solvent -borne. Based on epoxy  
resin and usually polyamide and  
supplied in two -pack form  Surface tolerant primer, usually 
containing a leafing  
aluminium pigment, is suitable for 
application not  
only to manually prepared steel 
surfaces, but also  
over existing, sound paintwork  
Advice should be sought when drying -oil/resin type paints are to be used over zinc -rich primers.  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    17  
Table 5 — Miscellaneous primers  
 
Ref. Description  General composition  Characteristics and usage  
5/1 Alkali -resisting  
primer  Traditionally solvent -borne.  
Typically, alkali -resistant drying oil  
(e.g. tung)/resin type binder,  
lightly pigmented  Although described as alkali -
resisting, primers of  
this type are intended for use on 
substantially dry,  
possibly alkali -containing, 
surfaces mainly  
beneath drying -oil resin finishes; 
they will not  
necessarily prevent attack by 
alkalis on  
subsequent coats if the structure 
is very damp  
5/2 Primer or  
primer  
undercoat  Water -borne (typically based on 
an acrylic polymer). Might be  
identical in composition to 4/9 or  
6/2 These primers are for use on dry 
plaster and similar surfaces. They 
might also be suitable for  
priming wood and building boards, 
metals  
(universal primer) and as 
undercoats (see 4/9 or  
6/2) 
5/3 Primer -sealer  
Other  
descriptions  
include  
stabilizing  
primer or  
solution,  
penetrating  
primer or  
masonry sealer  Traditionally solvent -borne and 
lightly pigmented, or 
semitransparent with a marker 
pigment, to assist even 
application. May also be based on 
fine particle -sized water -borne  
acrylic  The e ssential function of a primer -
sealer is to bind down powdery or 
friable residues of previous 
coatings which cannot be 
removed completely.  
Too much reliance should not be 
placed on the ability of this type of 
material to penetrate unsound 
coatings of substa ntial thickness, 
and as much as possible of the 
old material should be removed.  
Primer -sealers can also be used 
to reduce absorption on surfaces 
of high or uneven porosity.  
Masonry sealers are usually 
formulated  
specifically for use on exterior 
surfaces an d might  
not be suitable for interior work: 
with other types, the reverse 
might apply. Reference should be  
made to the manufacturer’s 
recommendations  
5/4 Universal  
primer (see  
also 5/2) All  
purpose primer  Typically, drying -oil/resin type  
binder or water -borne acrylic with  
white or light -coloured pigments,  
usually including rust -inhibitive  
types, e.g. zinc phosphate  A universal primer is typically 
white or light grey  
and is convenient for small -scale 
maintenance  
work involving patch -priming of a 
variety of substrates, e.g. wood, 
metal and dry plaster. For  
new and large -scale work, primers  
18  © KEBS 2018 — All rights reserved  Ref. Description  General composition  Characteristics and usage  
formulated for  
specific substrates are generally 
to be preferred  
 
 
 
Table 6 — Undercoats  
 
Ref. Description  General composition  Characteristics and usage  
6/1 Solvent -borne Traditionally 
drying -oil/resin type This type 
of undercoat provides a matt 
or low sheen  
undercoat    
6/2 Water -borne undercoat or 
primer undercoat  Based on acrylic or other 
polymers pigmented as in 6/1. 
Might be identical in composition 
to 5/2. These undercoats are quicker 
drying than 6/1 and, in normal 
conditions permit same -day 
recoating. General usage as 6/1. 
As primers they might be suitable 
for priming dry plaster, building 
boards and wood. Only types 
conforming to BS 7956  should be 
used for priming exterior 
woodwork.  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    19  
Table 7 — General pigment finishes  
 
Ref. Description  General composition  Characteristics and usage  
7/1 Solvent -borne  
gloss or midsheen  
finish Other  
descriptions  
include hard -gloss  
enamel and high gloss  
for gloss  
finishes; and  
eggshell, satin,  
silk and semi -gloss  
for midsheen  
finishes  Based on drying -oil/alkyd resin 
binder which might contain small 
amounts of polyurethane or other 
resins to increase hardness, 
flexibility or durability. Pigmented 
with 
titanium dioxide and/or lightfast, 
colored pigments  These are protective and 
decorative finishes suitable for 
interior and exterior use on most 
building surfaces. They have good 
durability and wearing properties 
in most conditions except those of 
direct chemical at tack or very high 
humidity.  
Advice should be sought from the 
manufacture regarding the 
suitability of mid -sheen finishes 
for exterior use on different 
substrates. For solvent borne 
gloss or mid -sheen finish, drying 
and 
recoating times are variable 
accordin g to composition but, 
usually, overnight drying between 
coats is required for drying -
oil/alkyd resin types For  
water -borne gloss or mid -sheen 
finish under normal  
conditions, drying and recoating 
times are  
considerably shorter than solvent -
borne and same  
day recoating is a possibility (see 
manufacturer’s  
instructions)  7/2 Water -borne gloss  
or mid -sheen  
finish Descriptive  
terms for sheen  
can be described  
as for 7/1  Typically based on acrylic 
dispersions. Might contain other 
modifying resins.  
Pigmented with titanium  
dioxide and/or light -fast, 
coloured pigments  
7/3 Solvent -borne  
matt or flat finish  Generally as for 7/1 adjusted  
to provide a matt finish  Essentially, this is a decorative 
finish for interior use only. Drying 
and recoating characteristics are 
usually similar to those of 7/1. 
Special purpose  
types, both water - and solvent -
borne designed for  
renovating surfaces which might 
be weak, liable to  
cause staining of subsequent 
coatings, or subject to  
further drying (see also 7/5)  
7/4 Water -borne matt  
or flat finish Other  
descriptions  
include emulsion  
paint, latex, vinyl  
or acrylic paint  
(see F.2.3)  Composition of binder typically  
based on vinyl or acrylic  
polymers or combinations of  
these, with titanium dioxide  
and/or coloured pigments  Water -borne are often less 
resistant than their  
solvent -borne counterparts, but 
the wear -resistance and 
washability of some might 
approach those of the 7/1 mid -
sheen finishes. They have 
advantages  
over the latter in ease of 
application to large areas,  
speed of drying (sam e-day  
20  © KEBS 2018 — All rights reserved  Ref. Description  General composition  Characteristics and usage  
recoating is usually  
possible), absence of solvent 
odour and ease of clean -up. They 
are widely used for ceilings and 
walls, mainly internally although 
some might be suitable for use on 
exterior walls. Choice of sheen 
level depends largely on location  
and aesthetic considerations but, 
in general terms, washability and 
resistance to soiling increase 
proportionately to the degree of 
sheen. Water -borne paints are  
generally more permeable to 
moisture than drying oil/  
resin finishes and only some are 
suitab le for use  
in situations where humidity is 
high for long periods,  
e.g. in kitchens and bathrooms 
(see manufacturer’s  
recommendations)  
7/5 Contract and  
general purpose  
paint  Water -borne. Composition,  
typically, is similar to that of  
7/4 but with higher pigment  
content and giving a matt  
finish  Higher pigment gives increased 
opacity, compared  
with 7/4 type, but at the expense 
of a reduction in washability and 
resistance to soiling. Paints of this  
type are frequently used for new 
interior walls and  
ceilings  where, apart from 
economy in use, their  
high permeability allows drying -
out of contained  
moisture  
7/6 Aluminium paint,  
general purpose (NWI 
proposal )  Traditionally, solvent -borne.  
Typically, drying -oil/alkyd resin  
binder pigmented with flake  
aluminium  The laminar nature of the pigment 
(see F.4.6)  
imparts moisture -resistance to 
aluminium paints,  
and their reflective and heat -
resistant properties are useful in 
many situations. They are suitable 
for use  
on most building surfaces, but 
their widest  
applicati on is on structural 
steelwork, storage  
vessels and heated metal 
surfaces  
7/7 Micaceous  
iron oxide  
paint, general  
purpose (NWI)  Solvent -borne. Typically, drying -oil 
or drying -oil/resin type binder 
pigmented with micaceous iron 
oxide. Small amounts of other  
pigments can be incorporated to 
modify the natural colour (dark 
grey) of the main pigment  Because of the laminar nature of 
the pigment (see  
F.4.6) and the substantial 
thickness of the film, micaceous 
iron oxide paints provide good 
protection and are widel y used 
extensively on structural steel, 
bridges, harbour installations and 
electricity transmission towers. On KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    21 Ref. Description  General composition  Characteristics and usage  
weathering, the coating develops 
a metallic sparkle. The dark colour 
of the  
pigment restricts the range of 
colours available, but  
over coating wi th alkyd gloss 
finish is often possible  
7/8 Masonry paint,  
water -borne,  
smooth or fine textured  Water -borne binder, typically 
based on acrylic, vinyl and other 
polymers formulated to have the 
degree of flexibility required for 
exterior use and pigmented with 
titanium dioxide and/or lime 
resistant coloured pigments.  
Some types are smooth; others 
contain fibre, sand or other agent 
to give a fine texture. Most contain  
an additive to inhibit mould and 
algal growth  These are essentially decorative 
coatings but  have the weather -
resistance and durability required 
in coatings for exterior walls. Both 
the smooth and the fine -textured 
paints can provide protection of 
concrete, etc. in combination with 
sealers, if needed, in accordance 
with manufacturer’s 
recommendat ions.  
These types of paint are not 
generally suitable for application 
to wood and metal. Formulations 
containing fibre, sand, etc. usually 
provide thicker films than the 
smooth types. The manufacturer 
should  
be consulted regarding the use on 
interior surfa ces of  
masonry paints containing 
additives to inhibit mould  
and algal growth because of the 
possible toxic hazard  
7/9 Masonry paint,  
water -borne  
heavy -textured  Compositions can vary 
considerably but consist generally 
of a heavy -bodied water -borne 
binder, reinforced with coarse 
extenders and in some cases, 
fibrous material and aggregates.  
Pigmentation is similar to that of 
7/8 and mould/algal inhibitors 
might be incorporated  Coatings of this type provide thick 
(1 mm to 2 mm),  
weather -resistant coatings, and  
experience indicates that they are 
capable of durability in excess of 
10 years. Their heavy texture is 
derived partly from their  
composition and partly from the 
method of  
application, typically by means of 
specially -designed rollers. In 
addition to their use externally, 
coatings of  
this type might be suitable for 
internal walls where a  
hard-wearing textured finish is 
required  
7/10 Masonry paint,  
solvent -borne,  
smooth or fine textured  Composition varies considerably.  
Older types can be based on a 
drying -oil/resin type binder, others 
on modified or synthetic rubber 
film-formers. Pigmentation is  
generally as for other masonry 
paints  The appearance of this type of 
coating is similar to that of the 7/8 
types, and film thickness is of the 
same order. Pe rmeability is 
usually lower, and the coating  
might therefore provide greater 
resistance to penetration by water 
and other agents, and scope for 
protective use, but it should be 
applied to dry substrates. Brush  
22  © KEBS 2018 — All rights reserved  Ref. Description  General composition  Characteristics and usage  
application will generally be 
slower than with  7/8 types. It is 
more tolerant of poor drying  
conditions than water -borne types  
7/11 Masonry  
paints,  
solvent -borne,  
thick, textured  Composition variable but typically 
employs a drying -oil resin binder; 
can be described as polyester (i.e. 
alkyd). Usually contains coarse 
extender and/or fibrous material.  
Pigmentation as for other masonry 
paints  These provide coatings of 
substantial thickness (0.6 mm to 
1.0 mm), of relatively low 
permeability, and therefore have 
good resistance to moisture 
penetration. Coati ngs of this type 
are usually applied by spray or 
roller, often by specialist 
contractors.  
Material and application costs are 
likely to be high  
7/12 Silicate -based  
masonry  
coatings  Water -borne. Based on water 
soluble silicates with possible 
addition of minor quantities of 
organic resins  The coatings are unusual in being 
based on an inorganic binder. 
They are suitable for external and 
internal surfaces. They provide 
inert non flammable  
films which are less affected than 
organic coatings by fungal and 
algal growth and are compatible 
with all mineral building materials. 
External surfaces to be painted 
should be free from dirt and all 
previous paint coatings. 
Application can be by brush, roller 
or spray.  
While drying, the coating can be 
very susceptible to ra in damage. 
The liquid paints are highly 
alkaline (caustic) and hence 
precautions should be taken 
during application. Resistance to 
moisture penetration can be  
improved by use of a hydrophobic 
impregnation  
treatment (e.g. silane, siloxanes)  
7/13 Cement paint to  
BS 4764 ((NWI)  Based on white Portland cement 
with titanium dioxide or coloured 
pigments, and additives to assist 
application and increase water -
repellence.  
Supplied in powder form and 
mixed with water immediately 
before application  Low-cost coatings giving a rough 
finish and used mainly for exterior 
wall surfaces, although they can 
be used inside except on gypsum 
plaster: not recommended for 
application over other types of 
paint. On lengthy outside 
exposure, pastel shades can tend 
to lighten and darker colours to 
become patchy. Can be used as a 
primer on  
uncoated exterior wall surfaces 
prior to finishes of type 7/9 or 7/10  
7/14 Multi -colour  
finish  There are different types of multi -
colour finish. In one type, droplets 
of pigmented resin solution are 
emulsified in an aqueous medium 
so that the coating is water -
thinnable. The pigmented droplets 
remain discrete in the dry film, so These are quick -drying, hard -
wearing finishes for  
interior wall surfaces, often used 
in circul ating areas, cloakrooms 
and similar hard -wear locations. 
Application  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    23 Ref. Description  General composition  Characteristics and usage  
providing the multi -colour effect. In 
another type, a pigmented 
emulsion -type basecoat is 
followed, when dry, by spray -
applied spatter coats of similar 
material.  
Alternatively, multi -colour patterns 
can be produced.  
Finally, an emulsion -type clear 
glaze -coat can be applied. In  a 
third type, a pigmented  
emulsion -type basecoat is  
followed, when dry, by a clear  
emulsion glaze in which are  
suspended multi -coloured  
flakes of solid material  is usually by spray, but materials 
of the third type might  
be suitable for brush or roller 
application  
7/15 Plastic texture  
paint  Typically, based on gypsum and 
supplied as dry powder for mixing 
with water before use, but ready -
for-use water -borne dispersion 
types are available.  
These may be referred to as 
synthetic resin plaster and do not 
necessarily contain gypsum. The 
term plastic  
indicates that the material can be 
worked after appl ication to provide 
relief texture effects  This is essentially a decorative 
coating for interior use only. It can 
be used as a substitute for plaster 
skimming on plasterboard ceilings 
or to disguise rough or cracked 
walls and ceilings. Texture is 
achieved e ither directly by 
spraying or by brush or trowel 
application and subsequent 
combing, stippling or other 
treatment.  
Some types are self -coloured and 
require no further treatment; 
others might require over -painting, 
e.g. with a water -borne paint.  
 
   
24  © KEBS 2018 — All rights reserved  Table 8  — Transparent and semi -transparent finishes for interior wood  
 
Ref. Description  General composition  Characteristics and usage  
8/1 Solvent -borne  
clear varnish,  
general  
purpose  Typically drying -oil/alkyd,  
urethane or urethane/alkyd  
resin  Used as a sealer on both 
softwood and hardwood surfaces. 
Available in a range of gloss from 
matt to full gloss. Some types 
might be sufficiently abrasion 
resistant for use on  
hardwood and softwood floors, 
counters and  
similar hard wear locations  
8/2 Water -borne  
clear varnish,  
general  
purpose  Water -borne acrylic copolymer  Fast drying, durable protective 
coating for most  
interior wood  
8/3 Water -borne  
clear floor  
varnish  Water -borne acrylic with  
polyurethane dispersion  High durability interior clear wood 
lacquer. Ideal heavy wear interior 
wood surfaces especially 
traditional floors. Resistant to 
common  
chemicals and hot water  
8/4 Semitransparent  
interior wood  
stain/dye  Coloured pigments or dyes,  
with or without drying -oil, water  
or solvent -borne  Used essentially to modify or 
enhance the  
appearance of interior wood 
without obscuring  
its grain and is usually over 
coated with a clear  
finish  
8/5 Solvent -borne  
two pack  
varnish  Typically oil, alkyd or polyol  
cured with aliphatic isocyanate  Limited potlife, some additional  
safety precautions required. Used 
in hard wearing  
areas, such as flooring  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    25  
Table 9 — Transparent and semi -transparent finishes for exterior wood  
 
Ref. Description  General composition  Characteristics and usage  
9/1 Clear varnish,  
solvent -borne  Typically drying -oil/phenolic or  
alkyd resin  This provides a tough water -
resistant coating,  
used principally as a clear 
protective finish for exterior 
hardwood. Usual mode of 
eventual failure  
by cracking and flaking, and in 
exposed situations  
demands frequ ent maintenance  
9/2 Solvent -borne  
two pack  
varnish  Typically oil, alkyd or polyol  
cured with aliphatic isocyanate  
with added UV absorber  Limited potlife. Used primarily on 
hardwoods.  
Similar to some yacht varnishes. 
Can give  
superior performance on 
hardwoods  
9/3 Semitransparent  
exterior wood  
stain, low -build,  
solvent -borne  Resins, pigments and  
fungicides in organic solvent  Relatively thin coating that 
normally imparts a noticeable 
sheen to the surface. Relatively 
high moisture vapour permeability 
and wood likely to be subject to 
dimensional movement and 
surface splitting. Not best suited 
to dimensioned  
components such as joinery  
9/4 Semitransparent  
exterior wood  
stain, low -build,  
water -borne  As for 9/3 minimizing the use of  
organic solvents  Relatively thin coating that 
normally imparts a noticeable 
sheen to the surface. Relatively 
high moisture vapour permeability 
and wood likely to be subject to 
dimensional movement and 
surface splitting. Not best suited 
to dimensioned components such 
as joi nery 
9/5 Semi -transparent  
exterior wood  
stain, medium build,  
solvent borne  Generally as for 9/3 but higher 
resin content.  Often used as top coat for 9/3. 
Because of its  
higher resin content this type of 
stain will confer a  
higher build and offers better 
control of moisture  
and dimensional movement  
9/6 Semi -transparent exterior 
wood stain, medium -build, 
water -borne  An alternative to 9/5 minimizing 
the use of organic solvents.  Often used as top coat for 9/4. 
Because of its  
higher resin content this type of  
stain will confer a  
higher build and offers better 
control of moisture  
and dimensional movement  
 
  
26  © KEBS 2018 — All rights reserved  Table 10 — Bituminous and tar -based coatings  
 
Ref. Description  General composition  Characteristics and usage  
10/1 Black paint (tar based)  
conforming to  
BS 1070, types  
A and B  Coal-tar or water gas -tar 
solutions  Moisture -resistant protective 
coatings for general use on metal 
and other surfaces where 
decorative appearance is 
unimportant. Both types are 
suitable for cold application, e.g. 
by brush. Type A is  
required to dry in 8 h and type B 
in 4 h  
10/2 Bitumen -based  
coatings  
conforming to  
BS 6949, types  
1 and 2  Bitumen solutions, type 2 with  
fillers  Generally as for 10/1. Type 1 
without fillers, type 2 with, 
permitting greater film thickness 
per coat. Not  
suitable for use in contact with 
drinking water (see  
10/3 for suitable types)  
10/3 Bitumen -based  
coatings  
conforming to  
BS 3416, types  
1 and 2  Bitumen solutions, type 2 with  
fillers  Generally as for 10/2, but suitable 
for use in contact with drinking 
wate r. Has to be certified under 
the 
Water Regulations Advisory 
SchemeA) in order to  
comply with EEC Directive 
80/778/EEC (as  
amended) [7]  
10/4 Bituminous  
emulsion  Water -borne bitumen  
emulsion  Black, water -thinnable moisture -
resistant coating.  
Typical use is as a waterproof 
membrane on  
exterior walls before application of 
water -borne  
masonry paints  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    27  
Table 11 — Specialist coatings  
 
Ref. Description  General composition  Characteristics and usage  
11/1 Two-pack epoxy  
primers,  
undercoats and  
finishes  Epoxy resin binder with amine or 
amide curing agent.  
Pigmentation according to  
end use, e.g. metal primers 
usually contain corrosion inhibitive 
pigments Primers are generally 
either zinc rich or zinc phosphate 
pigmented.  
Undercoats often contain MIO 
pigments. Bo th solvent -borne and 
water -borne epoxy coatings are 
available  Resistant to some acids and weak 
alkalis, oils, solvents and abrasion 
and used for protection of 
surfaces, especially steelwork, in 
severe conditions where coatings 
of conventional type are 
inadequate. Should be applied 
only to stable, well -prepared 
surfaces. Blast cleaning of 
steelwork is essential. Might not 
be suitable for application to 
gypsum plaster; a cement plaster 
base is preferable. Application to 
substrates liable to significant 
dimens ional change (e.g. external 
woodwork) can result in cracking 
of the film. Curing is temperature -
dependent, and the 
manufacturer’s recommendations 
in respect of ambient and surface 
temperatures should be observed. 
High humidity during  
application and curing  can also 
affect the coatings  
11/2 Two-pack coal tar  
epoxy  
coatings  
Replaced by  
hydrocarbon  
epoxies  Binder blended with  
hydrocarbon resins and  
mineral extenders  General characteristics as 11/1 
but lower resistance to solvents. 
Main use is for protection in 
conditions of very  
high humidity or immersion in 
fresh or seawater  
11/3 Two-pack  
polyurethane  
pigmented  
coatings,  
principally  
finishes  Acrylic modified polyester  
resin binder with  
polyisocyanate curing agent  
and white or coloured  
pigments  General characteristics as 11/1, 
but low temperature curing is 
usually better and sensitivity to 
moisture curing greater than with 
epoxies. Principal usage is as 
non-yellowing chemical -resistant 
finishes over epoxy primers and 
undercoats. These products 
contain  
isocyanates and need to be 
handled in accordance  
with relevant HSE requirements  
11/4 One-pack  
moisture -curing  
polyurethane  
primers,  
undercoats and  
finishes  Polyether isocyanate binder.  
Pigmentation according to  
end use  Resistant to some acids and weak 
alkalis, oils, solvents and 
abrasion; and used for the 
protection of steel and concrete 
surfaces in severe conditions 
where coatings of conventional 
type are inadequate. Apply only to 
stable, well prepared surfaces. 
Blast -cleaning of steelwork is 
essential. M ight not be suitable for 
application on gypsum plaster; a  
28  © KEBS 2018 — All rights reserved  Ref. Description  General composition  Characteristics and usage  
cement plaster base is preferable. 
The film might crack if applied to 
substrates liable to significant 
dimensional change (e.g. external 
woodwork). Curing is humidity -
dependent and to some extent 
temperature -dependent. Observe 
the manufacturer’s 
recommendations in respect of 
humidity and temperature. Most 
formulations can tolerate traces of 
surface moisture  
11/5 Acrylated rubber  
primers,  
undercoats and  
finishes  Acrylated rubber, pigmented  
according to end use, as  
11/1. Some types can be modified 
with drying -oil/alkyd resin. 
Formulations yielding  
coatings of substantial  
thickness are available  Suitable for use on most 
substrates and, as one -pack 
products, are more convenient to 
use than two -pack epoxy  and 
polyurethane coatings, although 
their chemical resistance might be 
lower. As for solution binders (see 
F.2.5), drying is essentially by 
evaporation and is less affected 
by low temperatures than is that 
of drying -oil/ resin, epoxy and 
polyurethane coat ings.  
Brush or roller application to large 
areas might be  
difficult, and spraying is 
recommended (see 9.3)  
11/6 Cellulose coatings, clear  
or pigmented,  
other than  
cellulose multicolor  
types  
(7/14)  Nitrocellulose/synthetic resin  
solutions clear or pigmented  Quick -drying coatings, having a 
limited application in the painting 
of buildings. As with other 
lacquers (see  
F.2.5) cellulose coatings are best 
applied by spray, although some 
types can be modified to allow 
brush applications to small areas. 
The most frequent usage is  
of clear and pigmented coatings, 
including “gold” and “bronze” 
lacquers for shop fronts, lift doors, 
ornamental metalwork and similar 
items, work usually carried out by 
specialists.  
NOTE This material has a high 
fire risk  
 
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    29  
Table 12 — Coating systems for interior wood  
 
Application (enduse)  Coating type  
(see Note 1)  Priming options for new 
and bare areas of wood 
(see also 8.1.6.3, 8.2.2.3, 
and Table 3)  Typical life to first 
maintenance  
(see Note 2)  
Opaque systems  
Internal surfaces of  
door and window  
joinery, wood trim,  
plywood and wood based 
boards  General purpose  
pigmented finishes as  
described in 7/1, 7/2, 7/3  
and 7/4  Opaque primer 3/1 
optionally  
over coated with 
undercoats  
6/1 or 6/2  Over 5 years  
Transparent and semi -transparent systems  
Internal surfaces of  
door and window  
joinery, wood trim,  
plywood and woodbased  
boards  Varnish, clear or 
semitransparent in wood 
tone of choice. Build and 
gloss level of choice. 
Abrasion  
resistant binder, e.g.  
polyurethane, for 
hardwear situations 
(Table 8)  Often primed with a 
suitably diluted coating of 
the finishing coat. Wood 
stains  
may be used to enhance  
grain  Variable according to  
type and service  
conditions but typically up  
to 5 years in average  
wear conditions  
Interior w ood stain in  
wood tone of choice,  
possibly overcoated with 
clear varnish  - Variable according to  
type and service  
conditions but typically up  
to 5 years in average wear 
conditions. Might  
give lifetime service in  
some situations  
Flooring  Varnishes with good 
abrasion resistance. See  
8/1 and 8/3. Specialist  
application may be  
required  Often primed with a 
suitably  
diluted coating of the 
finishing coat. Wood 
stains  
may be used to enhance  
grain  Long life in domestic  
situations but will require  
maintenance in high 
traffic areas  
NOTE 1 Wood coatings are described by many terms including colour, build and opacity; BS EN 927 -1 gives an account of 
terminology. Systems that do not fully obliterate the colour or grain of wood are sometimes described as natural finis hes. Coating 
systems can be based on different chemistries, e.g. alkyds and acrylics, and can be carried in either water or solvent. For i nterior 
use the latter are being phased out in response to environmental legislation.  
NOTE 2 Interior coatings will no t require frequent maintenance unless mechanically damaged. Transparent wood coatings could 
have some colour change.  
 
   
30  © KEBS 2018 — All rights reserved   
Table 13 — Coating systems for exterior wood  
 
Application (end use)  Coating type  
(see Note 1)  Priming options for new 
and bare areas of wood 
(see also 8.1.6.3, 8.2.2.3, 
and Table 3)  Typical life to first 
maintenance  
(see Note 2)  
Opaque systems  
Exterior door and  
window joinery  1 or 2 coats general -
purpose  
alkyd -based gloss paint 
over 
recommended undercoat  Opaque solvent -borne or  
water -borne (3/2 or 3/4), 
or 
preservative primer (3/6)  3 to 5 years  
1 or 2 coats flexible 
exterior alkyd -based paint 
over recommended 
primer. Gloss  
level and colour of choice  Opaque solvent -borne or 
water -borne (3/2 or 3/4), 
or preservative primer 
(3/6).  
Special primer/undercoats 
may be specified.  Over 5 years  
1 or 2 coats exterior 
waterborne paint (7/3). 
Gloss level  
and colour of choice  Opaque solvent -borne or  
water -borne (3/2 or 3/4), 
or 
preservative primer (3/6)  Over 5 years  
Softwood and  
plywood for  
cladding,  
bargeboards,  
soffits and fascias  1 or 2 coats flexible 
exterior alkyd -based paint 
over recommended 
primer. Gloss level and 
colour of choice  Opaque solvent -borne or  
water -borne (3/2 or 3/4), 
or 
preservative primer (3/6)  Over 5 years  
1 or 2 coats exterior 
waterborne paint (7/3). 
Gloss level  
and colour of choice  Opaque solvent -borne or  
water -borne (3/2 or 3/4), 
or 
preservative primer (3/6)  Over 5 years  
NOTE 1 Wood coatings are described by many terms including colour, build and opacity; BS EN  927-1 gives an account of 
terminology. Systems that do not fully obliterate the colour or grain of wood are sometimes described as natural finishes. Co ating 
systems can be based on different chemistries, e.g. alkyds and acrylics, and can be carried in eit her water or solvent. For interior 
use the latter are being phased out in response to environmental legislation.  
NOTE 2 Interior coatings will not require frequent maintenance unless mechanically damaged. Transparent wood coatings could 
have some colour change.  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    31  
Table 13 — Coating systems for exterior wood (continued)  
 
Application (end use)  Coating type  
(see Note 1)  Priming options for new 
and bare areas of wood 
(see also 8.1.6.3, 8.2.2.3, 
and Table 3)  Typical life to first 
maintenance  
(see Note 2)  
Transparent and semi -transparent systems (see Note 3)  
Exterior softwood door  
and window joinery  Exterior wood stain  
Medium -build (9/5 or 9/6)  3/6 or 3/3  Depends on product  
type, unlikely to exceed 2  
to 3 years on full exposure  
Exterior hardwood door  
and window joinery  
(see Note 4)  Exterior wood stain  
Medium -build (9/5 or 9/6)  3/6 or 3/3  Typically 3 to 5 years  
Depending on exposure  
Exterior grade plywood,  
e.g. door panels  Exterior wood stain  
Medium -build (9/5 or 9/6)  3/6 or 3/3  Depends on product  
type, unlikely to exceed 2 
to 3 years on full 
exposure.  
Efflorescence is a risk  
factor  
External softwood  
boarding, cladding,  
bargeboards, soffits,  
fascias  Exterior wood stain Low 
build  
(9/3 or 9/4) Medium build  
(9/5 or 9/6)  3/6 or 3/3  3 to 5 years depending  
on exposure  
External hardwood  
boarding, cladding,  
bargeboards, soffits,  
fascias  Exterior wood stain  
Medium -build (9/5 or 9/6)  3/6 or 3/3  4 to 5 years depending  
on exposure  
External grade plywood  
boarding, cladding,  
bargeboards, soffits,  
fascias  Exterior wood stain  
Medium -build (9/5 or 9/6)  3/6 or 3/3  Typically 3 to 5 years 
depending on exposure.  
Efflorescence is a risk  
factor  
Gates, fences,  
handrails, decking and  
garden furniture (see  
Note 5)  Exterior wood stain  
Medium -build ((9/5 or 9/6)  
Low-build (9/3 or 9/4) (see  
Note 3)  3/6 or 3/3  3 to 5 years  
NOTE 1 Wood coatings are described by many terms including colour, build and opacity; BS EN 927 -1 gives an account of 
terminology. Systems, which do not fully obliterate the colour or grain of wood, are sometimes described as natural finishes or 
exterior wood stains. Coating systems can be based on different chemistries, e.g. alkyds and acrylics, and can be carried in 
either water or solvent.  
NOTE 2 Life expectancies shown assume application to dry, sound  timber which, if necessary, has received preservative 
treatment and are based on performance in moderate environments as defined in Table 2. Lifetime expectations are expressed 
as an average and a distribution (standard deviation) around the average can b e expected in real situations. BS EN 927 -3 
provides a performance specification for exterior wood coatings.  
NOTE 3 The final appearance of transparent and semi -transparent coatings will depend on the number of coats. Two is the usual 
minimum; an additional  coat will increase service life but may darken the appearance. Penetrating low -build stains are primarily 
used on rough sawn timber where one or two coats are required.  
NOTE 4 Commercial systems designed for hardwood might have a different composition to their softwood counterparts.  
NOTE 5 Commercial variants might include different degrees of water repellence.  
  
32  © KEBS 2018 — All rights reserved   
Table 14 — Paint systems for iron and steel except heated surfaces  
 
Surface condition,  
primer and reference  
in Table 4  Finishing system and  
references in Table 6 
and Table  
7 Total film  
thickness μm  Typical life to first  
maintenance in  
exposure conditions  
indicated (see Note 1)  
Manually cleaned  
2 coat primer, e.g. 4/5  2 coats aluminium paint 
(7/6);  
or 
1 coat solvent -borne 
undercoat  
(6/1) and 1 coat alkyd 
gloss finish  
(7/1) 
or 
2 coats of gloss finish;  
or 
2 coats micaceous iron 
oxide  
(MIO) paint (7/7 high -build 
type)  
(see Note 3)  125 to 150  Interior  
Up to 10 years  
1 coat primer, e.g. 4/5  2 coats aluminium paint 
(7/6);  
or 
1 coat solvent -borne 
undercoat  
(6/1) and 1 coat alkyd 
gloss finish  
(7/1) or 2 coats of gloss 
finish;  
or 
2 coats micaceous iron 
oxide  
paint (7/7 high -build type) 
(see 
Note 3)  85 to 115  Interior  
Up to 5 years  
Exterior  
Not recommended  
Blast -cleaned  
2 coats oil -primer, e.g.  
4/5 1 coat solvent -borne 
undercoat  
(6/1) and 2 coats alkyd 
gloss  
finish (7/1) or 2 
undercoats and 1  
coat of gloss finish (see 
Note 2);  
or 
2 coats micaceous iron 
oxide  170 to 205  Interior  
Over 10 years  
 
 
 
 
 
 
 
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    33 Surface condition,  
primer and reference  
in Table 4  Finishing system and  
references in Table 6 
and Table  
7 Total film  
thickness μm  Typical life to first  
maintenance in  
exposure conditions  
indicated (see Note 1)  
paint (7/7 high -build type) 
(see 
Note 3)  Exterior  
Up to 10 years  
1 coat primer, e.g. 4/5  1 coat solvent -borne 
undercoat  
(6/1) and 2 coats alkyd 
gloss  
finish (7/1);  
or 
2 undercoats and 1 coat 
of gloss  
finish (see Note 2);  
or 
2 coats micaceous iron 
oxide  
paint (7/7 high -build type) 
(see 
Note 3)  115 to 145  Interior  
Up to 10 years  
Exterior  
Up to 5 years for film  
thicknesses exceeding  
125 μm  
NOTE 1 Life expectancies are based on performance in moderate exposure conditions as defined in Table  
2. NOTE 2 Mid -sheen alkyd finish (7/3) can be used in  mild interior exposure conditions.  
NOTE 3 MIO paint can be covered with alkyd gloss finish (if manufacturer approves) to provide specific colour.  
NOTE 4 Zinc rich primers (e.g. 4/7) are also used but problems can arise with many or drying -oil/resin system s, advice needs to 
be sought regarding compatible top coats (see also 11.3.2).  
 
   
34  © KEBS 2018 — All rights reserved   
Table 15 — Site pre -treatment and priming of non -ferrous metals and stainless steel (not 
factory pre -treated)  
 
Substrate  Surface preparation and pretreatment/priming  
Aluminium, smooth surfaces, e.g.  
sheets, extrusions and aluminized  
steel  Degrease (see 8.4.2.2). Abrade (see 8.4.2.7) and/or apply treatment 
primer (4/4). Then prime using zinc phosphate (4/5)  
Aluminium, rough surfaces, e.g.  
castings and sprayed metallic  
coatings  Abrade lightly (see 8.4.2.7) remove dust and dirt. Sprayed metallic 
coatings might require washing (see 8.4.2.3). With sprayed metallic 
coatings, pre -treatment primer (4/4) should be applied immediately 
following application of the coating (see 8. 4.3.4). Then prime using  
zinc phosphate (4/5)  
Zinc sheet, zinc (hot -dip galvanized,  
sherardized and electroplated)  
coated steel, zinc aluminium alloy  
(hot dip) coated steel  Degrease (see 8.4.2.2); abrade coated sheet metal components as 
necessary (see 8.4.3.3); apply pre -treatment primer (4/4) or treat with 
mordant solution (4/3). With sherardizing or if suitable primer is used 
on other coatings, weathering or application of pre -treatment primer is 
not needed. Some hot dip coatings might need de -nibbing A) and 
careful abrasion to remove surface deposits and sharp points  
Zinc and zinc aluminium alloy,  
sprayed  Sprayed metallic coatings might require washing (see 8.4.2.3). Apply 
pre-treatment primer (4/4) or treat with mordant solution (4/3). With  
sprayed metallic coatings, this should immediately follow application of 
the coating (see 8.4.3.4). If painted at a later time first remove dust  
and dirt; wash surface if necessary  
Copper, brass, bronze  Degrease (see 8.4.2.2). Abrade lightly (see 8.4.2.7) or appl y 
pretreatment primer (4/4)  
Lead  Abrade WET (see 8.4.2.7 and for health and safety guidance, see  
B.1.2). Apply pre -treatment primer (4/4)  
Cadmium coatings  Degrease (see 8.4.2.2). Abrade lightly (see 8.4.2.7). Apply 
pretreatment  
primer (4/4)  
Tin coatings  Degrease (see 8.4.2.2). Abrade lightly (see 8.4.2.7)  
Chromium and nickel coatings (if  
corroded)  Abrade (see 8.4.2.7) to remove corrosion products. Apply 
pretreatment  
primer (4/4)  
Stainless steel (see 8.3.2.2)  Degrease (see 8.4.2.2). Abrade (see 8.4.2.7). Apply pre -treatment  
primer (4/4)  
A) De -nibbing should take place before delivery to site. If this does not happen, it is essential that de -nibbing takes place prior to 
painting.  
NOTE 1 For specialist advice on substrates listed in this table, check with the coatings manufacturer.  
NOTE 2 Abrasion of metals may detract from the aesthetic appearance of the overall finish.  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    35  
Table 16 — Coating systems for internal plaster, concrete, brick, block and stone  
 
Substrate  
condition  Finish type and  
reference in Table 7  Primer and reference in  
Table 5  Coating system and 
references in Table  
6 or Table 7  
DRY r.h.  
below 75%  
(see Note 1)  Gloss, mid -sheen or  
matt (7/1, 7/2, 7/3)  Alkali -resisting primer  
(5/1) or, plaster only,  
water -borne primer (5/2)  Gloss finish: 1 coat solvent -
borne (6/1) or  
water -borne (6/2) undercoat; 1 
coat alkyd  
gloss finish (7/1) or 1 coat 
water -borne  
(7/2) 
Mid-sheen finish:  
2 coats alkyd mid -sheen finish 
(7/1) or 2  
coats water -borne (7/2)  
Matt-finish:  
2 coats alkyd matt  finish (7/3) or 
2 coats water -borne (7/4)  
General purpose  
emulsion paint (7/4,  
7/5) Primer not usually required 
but see 8.5.1.4 and 8.5.1.5. A 
well thinned  
first coat of  
water -borne paint might  
be required on surfaces  
of high or variable  
porosity (see 8.6.2.4)  Matt or mid -sheen finish: 2 or 3 
coats  
general purpose water -borne 
paint, matt or  
mid-sheen (7/4)  
Matt, high -opacity finish: 2 
coats contract  
water -borne paint (7/5) 1 coat, 
spray applied,  
might suffice in some situations  
Multi -colour (7/14)  Primer or basecoat as  
recommended by  
manufacturer  Usually 1 coat multi -colour 
finish (7/14)  
spray -applied but refer to 
manufacturer’s  
instructions  
Textured (7/15)  Primer not usually  
required but refer to  
manufacturer’s  
instructions  Plastic texture paint  (7/15): 
Normally 1 coat  
but might require over -painting  
Water -borne masonry paint, 
heavy -texture  
(7/9):  
Normally 1 coat but refer to 
manufacturer’s  
instructions  
Masonry paint,  
mineral type (7/12)  Check with manufacturer  Check with manufacturer  
Cement paint (7/13)  
(not on gypsum plaster)  Primer not required  1 or 2 coats cement paint (7/13)   
36  © KEBS 2018 — All rights reserved  Substrate  
condition  Finish type and  
reference in Table 7  Primer and reference in  
Table 5  Coating system and 
references in Table  
6 or Table 7  
DRYING  
Some damp  
patches might  
be evident, r.h.  
75% to 90%  Water -borne paint  
(7/4, 
7/5) As for DRY substrates  Matt or mid -sheen finish:  
2 or 3 coats general purpose 
water -borne  
paint, matt or mid -sheen (7/4)  
Matt, high -opacity finish: 2 
coats contract  
water -borne paint (7/5) 1 coat, 
spray applied,  
might suffice in some situations  
Multi -colour finishes  
(7/14) possible but  
consult  
manufacturer  As for DRY substrates  Usually 1 coat multi -colour 
finish (7/15)  
spray -applied but refer to 
manufacturer’s  
instructions  
Textured paints  
(7/15) possible but  
consult  
manufacturer  As for DRY substrates  Plastic texture paint (7/15):  
Normally 1coat but might 
require overpainting  
Water -borne masonry paint, 
heavy texture  
(7/9):  
Normally 1 coat but refer to  
manufacturer’s instructions  
If over coating is necessary, 
water -borne  
paint should be used  
Masonry paint,  
mineral type (7/10)  Check with manufacturer  Check with manufacturer  
Cement paint (7/11)  
(not on gypsum  
plaster)  Primer not required  1 or 2 coats cement paint (7/13)  
DAMP  
Obvious damp 
patches, r.h.  
90% to 100%  Water -borne paint  
(7/4, 
7/5) possible, but  
consult coating  
manufacturer  Primer not recommended  Matt or mid -sheen finish:  
2 or 3 coats general purpose 
water -borne  
paint, matt or mid -sheen (7/4)  
Matt, high -opacity finish:  
2 coats contract water -borne 
paint (7/5) 1  
coat, spray -applied, might 
suffice in some  
situations  
Contract types (7/5) are usually 
more  
permeable than general 
purpose (7/4)  
types and less prone to failure 
on damp  
substrates  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    37 Substrate  
condition  Finish type and  
reference in Table 7  Primer and reference in  
Table 5  Coating system and 
references in Table  
6 or Table 7  
Masonry paint,  
mineral type (7/12)  Check with manufacturer  Check with manufacturer  
Cement paint (7/13)  
(not on gypsum  
plaster)  Primer not required  1 or 2 coats cement paint (7/13)  
WET  
Moisture visible 
on surface, r.h.  
100%  Cement paint (7/13)  
(not on gypsum  
plaster)  Primer not required  1 or 2 coats cement paint (7/13)  
NOTE 1 For information on the repair of concrete structures, see BS EN 1504 -2 and BS EN 1504 -10. 
NOTE 2 For information on the selection of coating systems for exterior masonry and concrete, see BS EN  
1062 -1. 
NOTE 3 r.h. refers to the relative humidity in equilibrium with the surface. See 8.5.1.1 for method of measuring moisture con tent. 
 
   
38  © KEBS 2018 — All rights reserved   
Table 17 — Coating systems for external renderings, concrete, brick, block and stone  
 
Substrate  
condition  Coating type  Primer and  
reference in Table  
5 Coating system 
and references in 
Table 6 or  
Table 7 and use  Typical life to  
first 
maintenance  
(see Note 2)  
DRY r.h.  
below 75%  
(see Note 1)  Masonry paints,  
solvent -thinned  
(7/10 or 7/11)  Alkali -resisting  
primer (5/1) or as  
recommended by  
manufacturer  Smooth or fine -
textured (7/10)  
types, solvent -
thinned 2 coats  5 years or more  
Thick, textured 
(7/11)  types,  
solvent -thinned  
10 years or more  
Usually 1 or 2 coats 
applied by  
spray, often by 
specialist  
applicators  10 years or more  
Water -borne  
masonry paints  
(7/8, 7/9)  Primer not usually  
required with 7/8  
types but see  
8.5.1.4 and 8.5.1.5  Smooth or fine-
textured (7/8)  
water -borne types 2 
coats  5 years or more  
Primer not usually  
required with 7/9  
types but refer to  
manufacturer’s  
recommendations  Heavy -textured 
(7/9) waterborne  
type Usually 1 coat  
applied by roller  10 years or more  
Masonry paint,  
mineral type  
(7/12)  Check with  
manufacturer  Check with  
manufacturer  Over 15 years  
Cement paint  
(7/13)  Primer not required  2 coats cement 
paint (7/13)  3 to 5 years  
Alkyd gloss and  
modified alkyd  
gloss (7/1)  Alkali -resisting  
Primer (5/1)  1 coat solvent -
borne  
undercoat (6/1); 1 
or 2 coats  
alkyd gloss finish 
(7/1) 3 to 5 years  
DRYING  
Some damp  
patches  
might be visible, r.h.  
75% to 90%  Water -borne  
masonry paints  
(7/8 or 7/9)  As for DRY  
substrates  Smooth or fine -
textured (7/8)  
water -borne type 2 
coats; or  
Heavy -textured 
(7/9) waterborne  
types Usually 1 coat  
applied by roller  Potentially as for  
DRY substrates  
but some risk of  
earlier failure at  
higher moisture  
levels  
Masonry paint,  
mineral type  Check with  
manufacturer  Check with  
manufacturer  Over 15 years  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    39 Substrate  
condition  Coating type  Primer and  
reference in Table  
5 Coating system 
and references in 
Table 6 or  
Table 7 and use  Typical life to  
first 
maintenance  
(see Note 2)  
(7/12)  
Refer to  
manufacturer’s  
recommendations  
for use of 
solventborne  
masonry  
paints (7/10 or  
7/11)  As for DRY  
substrates  Smooth or fine -
textured (7/10)  
types, solvent -borne 
2 coats;  
or Thick, textured 
(7/11) types,  
solvent -borne 
Usually 1 or 2  
coats applied by 
spray, often  
by specialist 
applicators  Potentially as for  
DRY substrates  
but some risk of  
earlier failure at  
higher moisture  
levels  
DAMP  
Obvious  
Damp patches, r.h.  
90% to  
100%  Masonry paint,  
mineral type (7/12)  Check with  
manufacturer  Check with  
manufacturer  Over 15 years  
Cement paint (7/13  Primer not  
required  2 coats cement 
paint (7/13)  As for DRY  
substrates  
Refer to  
manufacturer’s  
recommendations  
regarding use of  
water -borne  
masonry paints (7/8  
or 7/9)  Primer not  
required  Smooth or fine -
textured (7/9)  
water -borne types 2 
coats; or  
Heavy -textured 
(7/10) waterborne  
types Usually 1 coat  
applied by roller  Potentially as for 
DRY  
substrates but high  
risk of earlier failure  
WET  
Moisture visible on 
surface r.h.  
100%  Cement paint (7/13)  Primer not  
required  2 coats cement 
paint (7/13)  As for DRY  
substrates but some  
risk of earlier failure  
NOTE 1 r.h. refers to the relative humidity in equilibrium with the surface. See 8.5.1.1 for method of measuring moisture con tent. 
NOTE 2 Life expectancies shown assume application to dry, sound substrates, qualified as indicated for other substrate 
conditions, and are based on performance in moderate external conditions as defined in Table 2. Aesthetic considerations migh t 
influence the need for maintenance.  
NOTE 3 For information on the repair of concrete structures, see BS EN 1504 -2 and BS EN 1504 -10. 
NOTE 4 For information on the selection of coating systems for exterior masonry and concrete, see BS EN 1062 -1. 
 
   
40  © KEBS 2018 — All rights reserved   
Table 18 — Site priming of fibre building board, wood chipboard and plaster board (not 
factory -primed or sealed)  
 
Type of board or sheet  Primers and references in Table 3 and Table 5  
 With solvent -borne finishes  With water -borne finishes A)  
Hardboard, medium board,  
medium density fiberboard  
(MDF) and soft board  Primer -sealer (5/3)  
Water -borne primer (5/2)  
Aluminium wood primer (3/2)  Not usually required, but, for  
absorbent board, first coats might  
need additional thinning  
Flame retardant treated  Alkali -resisting primer (5/1)  Alkali -resisting primer (5/1)  
Soft board, bitumen -impregnated  Aluminium wood primer (3/2)  Not usually required  
Wood chipboard  Solvent -borne wood primer (3/1)  
Primer -sealer (5/3)  
Water -borne primer (5/2)  
Aluminium wood primer (3/2)  Not usually required except possibly  
that solvent -borne primer (3/1, 3/2 
or 
5/3) is recommended for single 
layer  
boards (see 8.2.1.3) to prevent  
swelling of chips  
Plasterboard  Primer -sealer (5/3)  
Water -borne primer (5/2)  Not usually required (see Note)  
Oriented Strand Board (OSB)  As wood chipboard  As with solvent -borne finishes if a  
high quality finish is required  
Cement bonded particleboard  Water -borne primer (5/2)  
Alkali -resisting primer (5/1)  Water -borne primer (5/2)  
Alkali -resisting primer (5/1)  
Water -borne multi -colour finishes (7/14) are usually applied over a special base coat.  
NOTE Refer to the plasterboard manufacturer's recommendations on priming for use with water -borne finishes.  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    41  
Table 19 — Paint film defects arising during, or shortly  after application  
 
Ref Defect name  Possible cause  Cure  
1 Bleeding  Solvent or water reactive stain,  
timber extractives, nicotine, tar or  
bitumen  Remove as much  
contamination as possible,  
seal with stain block primer,  
alkali resisting primer or  
aluminium wood primer  
2 Blooming, or milky  
appearance usually gloss  
paint, also slight matting of  
the gloss  Cold temperatures, high humidity 
and/or moisture, during the drying 
process of the paint. Usually  
associated with winter months  Abrade and re -coat 
3 Ropiness (brush marks)  Poor flow of the paint, over  
brushing, rapid drying, etc.  Abrade and re -coat 
4 Cissing (separation of paint  
film whilst wet)  Surface contamination, wax,  
grease, sometimes occurs when  
applying water -borne paint over  
poorly prepared oil-based paint  Remove as much  
contamination as possible,  
degrease, use a silicone 
digester, abrade and re -coat.  
Ensure application tool is also  
free from contamination  
5 Sleepy gloss (low sheen)  Sinkage into substrate, due to  
incorrect or insufficient primer or  
undercoat, medium density fibre  
board paraffin wax contamination  For medium density fibre  
board, abrade and then apply  
acrylic primer conforming to  
BS 7956, then re -coat. Other  
surfaces may simply require  
re-coating  
6 Flashing (halo effect where  
two edges of paint meet)  Losing the wet edge of the paint  
during application, trying to “touch  
up” areas, especially sheen 
paints,  
but can occur with all paints  Re-paint to the nearest whole  
elevation, ensuring the wet  
edge is maintained  
7 Curtains, runs, sagging,  
floatation of pigment  Over application, i.e. too much 
paint  
applied unevenly  Allow excessively thick areas 
to harden (sometimes scraping 
off excess thickness will be 
required). Abrade and re -coat 
8 Cracking/crazing  Usually associated with applying a  
fairly brittle paint over a highly  
flexible layer, i.e. matt over silk  Abrade, correctly prime, i.e. 
alkali resisting primer and 
recoat.  
Severe instances may  
require lining paper  
9 Pickling (looks like wrinkling)  Solvent attack, i.e. applying  
chlorinated rubber paint over a  
conventional paint, solvents act as 
a 
stripper  Complete removal of all  
affected coatings may be  
required   
42  © KEBS 2018 — All rights reserved  Ref Defect name  Possible cause  Cure  
10 Wrinkling, rivelling,  
shrivelling  Application too thick, usually gloss 
paints, the paint layer skins over 
but remains wet underneath. Can 
also 
be caused by over coating before  
previous layer is dry  Allow affected areas to  
harden, abrade with wet and  
dry abrasive paper to smooth,  
and re -coat 
11 Rain spotting (also known as  
pitting)  Rain/water attack during the 
drying  
phase  Wet abrade to smooth, re -coat 
12 Bittiness  Contaminated paint, dusty  
atmosphere, substrate not clean,  
application tool not clean  Abrade, re -coat, ensure  
application tools are clean,  
strain the paint  
13 Orange peel effect  Application by roller without laying 
the paint off with a brush (such as 
applying gloss to doors). Poor 
atomization when spraying  Wet abrade to smooth, re -coat 
using correct method and  
adjustment  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    43  
Table 20 — Paint film defects arising after a period of exposure  
 
Ref Defect  Typical causes  Remedial treatment  
1 Adhesion failure  a) Application to damp, dirty or  
weather -degraded substrates,  
substrates contaminated by 
biological  
growth; or subsequent entry of  
moisture, e.g. through open joints 
in 
woodwork  Flaking, peeling or poorly 
adhering coating should be 
removed (see 11.5.2) and any 
damaged substrate repaired 
(see 8.1.4.2). Biological  
growths should be removed 
(see 11.5.8). Where moisture is 
the cause, it should be ensured 
that the substrate is dry before 
repainting. See 8.1.3 in  
relation to sources of moisture 
in woodwork  
b) Failure to prepare or pre -treat 
nonferrous  
metals  Defective material should be 
removed.  
See 8.4.2 for preparation of 
non-ferrous metals  
c) Omission of primer or use of  
unsuitable primer  Defective material should be 
removed.  
Refer to appropriate substrate 
in Clause 8 for information on 
priming  
d) Application to powdery or friable  
substrates  Defective material should be 
removed.  
Applica tion of a penetrating 
primer or sealer might be 
necessary (see 11.5.5)  
e) Application to hard, dense  
substrates, e.g. glass or glazed  
surfaces  Defective material should be 
removed.  
See 8.14 for subsequent 
preparatory treatment  
f) Apparent loss of adhesion on iron  
and steel, might be due to  
detachment of millscale  Removal of millscale, e.g. by 
blast cleaning  
or flame cleaning, might be 
impracticable as a maintenance 
operation and is costly, hence 
the desirability of effective initial 
preparation. There might be no 
alternative to manual cleani ng 
to remove millscale as it 
loosens, but this might extend 
over several repaints  
2 Blistering  Blistering is usually indicative of 
liquid or vapour beneath the 
coating. The presence of water is a 
frequent cause. On painted 
woodwork, migration of water 
vapour from the inside of a building 
through the wood can cause 
blistering if the internal and exte rnal 
coatings do not provide the Depending upon the extent and 
severity of blistering, 
preparation might be confined 
to removal of isolated blisters or 
compl ete stripping might be 
necessary. Where moisture is 
the cause, time should be 
allowed for drying out. (See 
also 8.1 in relation to sources of  
44  © KEBS 2018 — All rights reserved  Ref Defect  Typical causes  Remedial treatment  
recommended differential 
permeability system. Resinous 
knots  
might also cause localized 
blistering  moisture in woodwork.)  
Blistering on resinous external  
woodwork might be influenced 
by choice of finishing colour  
3 Chalking,  
powdering  Slow erosion and chalking on 
lengthy exposure, especially 
externally, is a characteristic of 
many paints and wood finishes. It is 
not usually regarded as a  
defect unless it occurs prematurely 
and 
profusely, when the causes might 
be as follows:  
a) conditions of exposure 
exceptionally severe;  
b) earlier coats in system have 
failed to satisfy porosity of 
substrate;  
c) incorrect or unsuitable 
formulation  In ab sence of other defects, 
lightly chalk ing surfaces might 
require only washin g and light 
abrasion to provide a 
satisfactory base for further 
coats.  
Heavily chalked or powdery 
surfaces will re quire more 
vigorous cleaning or abrasion 
combined if necessary with 
application of a penetrating 
primer  
(see 11.5.5)  
4 Colour defects, e.g. fading, 
staining, bleeding, or  
other forms of discoloration  a) Some loss of colour of paint 
might occur on lengthy exposure to 
bright sunlight but is not usually 
significant.  
Early loss of colour might be due to 
use in unsuitable conditions, e.g. 
external use of a colour intended 
only for interior use.  
Chemical attack might cause 
change or loss of colour  If necessary, consult 
manufacturer regardin g 
selection of colours or types of 
finish for repainting  
b) Solvent -borne finishes tend to 
yellow in situations where direct 
daylight is excluded. This is more 
obvious with white and light -
coloured finishes  Yellowing is not usually 
sufficiently marke d to be 
significant. If freedom from 
yellowing is important, consult 
manufacturer for gui dance on 
selection of oil -free coatings  
c) Appa rent colour change might 
be due to maskin g of colour by 
surface chalking (item 3 of this 
table) to efflorescence (see  
8.5.1.2) especial ly on external 
rendering or, on external plywood 
treated with wood stain,  
to diffusion of water -soluble salts  
contained in adhesives  Normal cleaning usually 
removes surface deposits. 
Efflorescence an d diffusion of 
salts on plywood might recur 
until source is exhausted  
d) Failure of clear finishes on  
external woodwork might result in 
discoloration of exposed wood  Clear finish should be removed 
completely. Sanding or scraping  
might remove discolorati on or 
damaged timber, but application 
of coloured wood stain might be  
necessary to achieve uniform  
appearance  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    45 Ref Defect  Typical causes  Remedial treatment  
e) Constituents of the substrate or  
previous coatings can cause  
discoloration (see 8.5.1.5 and  
11.5.9)  See 8.5.1.5 and 11.5.9  
5 Cracking, other than  
that due to structural  
movement  Cracking is usually indicative of 
stresses within the coating film, 
caused, for example, by applying 
hard-drying coatings over soft 
coatings. It might also be the initial 
stage in adhesion failure (item 1 of 
this table).  
Cracks might be confined to the 
finishing coat or extend through  
the thickness of the film  If cracking is sligh t and confined 
to the finishing coat, light 
abrading might provide a 
satisfactory base for recoating. 
If cracking is severe or extends 
through the thickness of the 
film, complete removal might be 
necessary  
6 Damage to coating  a) Mechanical damage, e.g. by  
abrasion, impact or vigorous 
cleaning  
b) Graffiti  Where surfaces are subject to 
hard wear, specialist coatings 
might be required (see 
4.6.4.6.2).  
Consid eration should also be 
given to the u se of wear -
resistant materials, e.g. ceramic 
tiles or plastics, where 
practicable. In relation to graffiti, 
see 
4.6.4.8  
7 Gloss, loss of  Some loss of gloss is to be 
expected after lengthy exposure, 
especially externally, and might be 
the first stage in chalking (item 3 of 
this table). Where it occurs 
prematurely, poss ible 
causes are as described for  
premature chalking  Loss o f gloss in the absence of 
other defect s is not usually 
significant in relation to 
maintenance treatment  
8 Biological growths, i.e.  
moulds, algae, lichen,  
moss, blue stain  See 4.6.4.4 and 11.5.8  See 4.6.4.4 and 111.5.8. 
Consider  
modifications to design or  
environment which might 
eliminate or  
reduce causes of failure  
9 Rust-spotting or rust staining  
on painted iron  
and steel  This usually indicates that the 
thickness of the paint system is 
insufficient to provide protection on 
peaks and edges. It might result 
from application of an inadequate 
system initially or at the last repaint 
or from erosion of the film during 
exposure. A further possible cause 
is failure to use a rust -inhibitive 
prime r 
(see F.4.5 and Table 4)  Depending upon the severity 
and extent of the defect, 
treatment might range from 
manual cleaning and priming of 
localized areas to overall 
removal of the coating and 
treatment as for new iron and 
steel (see 8.3).  
Consideration should be given 
to increasing the film thickness 
of the  
system or to reducing the 
intervals between repaints until 
an adequate thickness has 
been built up   
46  © KEBS 2018 — All rights reserved  5 Organization of work  
 
5.1  General  
 
Where applicable, painting work should be planned in relation to the work of other trades (see 5.3), to ensure 
that surfaces are in a fit condition to be painted and that completed work is not damaged by subsequent 
building operations; in particular, time should be allowed for drying out of plaster and similar surfac es before 
they are painted.  
 
In factories and commercial buildings, it might be necessary for work to proceed without interrupting the 
normal functions of the building. This should be planned carefully to avoid inconvenience to the occupants 
and minimize loss of productive time by the contractor. In such circumstances, it might be necessary to erect 
temporary partitioning to isolate the areas where painting is in progress.  
 
5.2  Health and safety  
 
The recommendations of Annex B should be followed, concerning the manner of dealing with typical hazards 
to health and safety that might be encountered in the painting of buildings.  
 
Information on the properties or constituents of coatings or other materials that affect health and  safety 
should be obtaine d from the manufacturer or supplier and the precautions set out in their safety data sheets 
and container labels should be followed. All preservatives should be handled with care in accordance with 
the manufacturer's specific instructions. Potential health  and safety hazards include but are not limited to the 
following:  
 
a) inhalation, absorption through the skin or ingestion of toxic substances, including fume s, vapours and  dusts; 
 
b) injury to eyes and skin; 
 
c) fire and explosion; 
 
d) noise; 
 
e) lack of personal hygiene. 
 
5.3 Order  of working 
 
When  buildings are painted internally and externally, the exteri or work should be completed fi rst, especially 
when it is necessary to Use ro oms and windows to gain access to the external surfaces or when painting  is 
carried out from the scaffo lding as it is struck. However, the determi ning fa ctor is often  weather or the time 
of year at which work is done. 
Work should be carried out from the upper parts of a building or structure downwards, application of p aint 
following preparation  in the same order, but circumsta nces mig ht require modification of this. If so, care 
should be taken to ensure th at finished work is not spoiled by  dust and debris arising fr om subsequent 
preparatory work. 
 
5.4 Scaffolding  and equipment  
 
Scaffolding should be adequate  in quantity and type to permit safe working and avoid delay s. Hazards can  be 
created by the use of unsui table or defective  scaffolding  and the guidance  should be followed. Equi pment 
should be suitable for the type of work being undertaken and in good condition. M echanic al equipment, e.g. 
for spray ing, should  be of  a ca pacity or rating appropriate to the work and sh ould operate  efficiently. 
Allowance should be made  for the provision  of temporary  heating or drying  equipment  where n ecessary. 
 
5.5 Supply of materials  
 
Most conventional decorative materials are available on demand or at short  notice from the manufacturer or 
distributor, but this might not apply  to all quantities, colours and container sizes or to sp ecialist  materials. 
Manuf acture of materials not normally  held in stock can take several  weeks, and orders should be placed  well in 
advance to avoid delay. KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    47  
Usually, placing of orders for materials is the responsibility  of the contractor, but early issue of painting 
schedules by spec ifiers reduces the risk of delay in supply that could cause work to be delayed. 
 
5.6 Storage of materials  
 
5.6.1  On large  projects, fa cilities should be provided for the storage of materials, having regard to 
security, avoidance of hazards and maint enance of materials in good condition. 
 
5.6.2  Some  coatings, other than water-borne types, are flamm able in the liquid state; precautions  to prevent 
accidental ignition should be taken and emergency fire-fighting equipment provided. If the total quantity of 
flammable paints, etc. in storage exceeds  50 l at any one time,  special  provisions  in should  be taken avoid 
accidents.  
 
5.6.3  Contain ers of highly  flammable li quids (flash points below 32 °C), which include certain solvents and 
specialist coatin gs, usually carry a warning label but, in case of doubt,  reference should be made to the  
manufacturer.  
 
5.6.4  To maintain coatings in good  condition  and to prevent rusting of containers and deterioration of dry 
materials, such as powder fillers, materials should  be stored  in dry conditi ons prefera bly within a tem perature 
range of 5 °C to 30 °C. Attenti on should be paid to the storage of coatings containing volatile  solvents, as 
temperatures exceeding 30 °C can create excessive pressure within containers and  increases the risk of fire. 
Water-borne coatings  shou ld be protected from frost. 
 
5.6.5  On contracts of long duration, when successive batches are delivered  at intervals, dates of receipt 
and batch numbers should be recorded and  storage organized so that the materials can be issued in the  same 
order as they were received. If batch numbers are missi ng or illegible, the containers should be marked with the 
date of receipt. 
 
5.7 Protection of components on site  
 
5.7.1  General  
 
Measures should be taken to prevent damage or deterioration of components and factory applied treatments 
on site, i.e. during off -loading, handling, storage and erection. If mechanical lifting equipment is used to 
handle large or heavy components, slings should be well padded at c ontact points. Wrapping or other means 
of protection provided by the manufacturer should not be removed before it is essential to do so. Factory 
coated articles and components should be stored away from areas subject to pedestrian or vehicle traffic 
and be  protected against damage and soiling.  
 
5.7.2  Joinery  
 
Where possible, joinery, primed or unprimed, should not be kept in external storage, especially when it is to 
be installed in a centrally heated building. If external storage cannot be avoided, the com ponents should be 
protected against moisture and other adverse climatic conditions. Components, whether stored indoors or 
outdoors, should not be in direct contact with the ground.  
 
If stacking is necessary, spacers should be placed between the components to permit air circulation and, in 
the case of primed joinery, to prevent sticking at contact surfaces.  
 
5.7.3   Metal components  
 
Where possible, metal components prepared and painted with part or the whole of the coating system before 
delivery to site shou ld, size permitting, be stored indoors. If external storage cannot be avoided they should 
be protected and stacked as described in 5.7.2.  
 
5.7.4  Structural steel members  
  
48  © KEBS 2018 — All rights reserved  Primed structural steel members, if stored externally, should be stacked in such a ma nner that they do not 
retain water even if no cover is provided. The bottom layer in the stack should be laid on timber packings to 
raise it above the ground and the rainwater splash zone. Spacers should be placed between subsequent 
layers to permit air ci rculation and prevent sticking.  
 
Consideration should be given to applying additional coats, e.g. of primer, when there is a possibility of long 
delay between initial and final painting after erection.  
 
5.8 Off-site work  
 
Many components, such as primed an d finished joinery, blast -cleaned and primed steelwork, pre - treated 
non-ferrous metal components and pruned or sealed building boards, are now factory coated off site. Where 
components are supplied partially -painted, e.g. primed, the treatment or coating should have properties 
appropriate to the exposure conditions or conditions of service. The primer (or other treatment) and coatings 
to be applied should be compatible.  
 
Measures should be taken to prevent damage to primed and finished components during tr ansit, as it might 
not be possible to effect repairs to a standard equal to that of the original. The painting specification for the 
site work should detail responsibility for repairing any damage. The manufacturer's or supplier’s 
recommendations for repai ring damage caused in transit or during installation and for subsequent 
maintenance treatment should be followed.  
 
5.9 Workforce and supervision  
 
5.9.1  The number of operatives employed should be appropriate to the size of the contract, its planned 
duratio n and the nature and availability of the work involved. Preparation is generally more labour intensive 
than application, and the size and deployment of the workforce should allow for this. On extensive ceiling 
and wall areas, there should be a sufficient n umber of operatives to ensure working wet edges are 
maintained (see 9.3.2.3) and should take into account working conditions and the characteristics of the 
coatings to be applied.  
 
5.9.2  Operatives should be skilled and experienced in the types of work inv olved and with the materials, 
methods and equipment to be used. With novel materials, methods or equipment, special training might be 
necessary.  
 
5.9.3  Adequate supervision should be provided, having regard to the nature of the work and the size and 
deploy ment of the workforce. Supervisors should be experienced in all aspects of the work for which they are 
responsible. They should be provided with copies of all working documents, e.g. specifications, painting 
schedules and product information necessary for effective supervision and control of the work. They should 
also be provided with, or have ready access to, test equipment, e.g. moisture meters, film -thickness gauges 
and flow cups, when the nature of the work requires it.  
 
5.10 Inspection procedures  
 
Inspection procedures should be carried out in accordance with Clause 10, which may necessitate the 
sampling and testing of materials on a regular basis (see 5.11 and 10.3).  
 
Note  For large contracts, specific stages of the work might be subject to inspection and approval by a 
nominated person or specialist inspection organization to ensure compliance with the specification. 
Inspection does not remove or diminish the contractor's responsibility for proper supervision of the work.  
 
5.11 Materials samp ling and testing  
 
The routine sampling and testing of materials should be carried out as described in Clause 10.  
 
NOTE   Sampling and testing procedures can be time -consuming and expensive and are effective only if 
they are properly implemented.  
6 Exchange of information  
 
6.1 General  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    49  
Specifications and other documents needed in respect of initial or maintenance painting should be prepared 
in sufficient detail to afford proper guidance in the preparation of estimates and the execution of the work.  
 
Where rel evant, there should be an exchange of information at an early stage between the painting 
contractor or subcontractor and those responsible for the constructional work, including other trades affect or 
be affected by painting.  
 
A painting project can involv e several parties, including client, main contractor and subcontractors, suppliers 
and inspectors. Copies of all relevant documents should be available to all parties, including site personnel 
responsible for supervision.  
 
6.2 Specification  
 
6.2.1  General  
 
A specification should be clear, concise and unambiguous. The prime functions of a specification for initial or 
maintenance painting are:  
 
a) to describe the substrates to be treated and the means by which the required finish is to be achieved 
including surface preparation, materials, systems, application methods (where relevant) and the conditions 
under which the work is to be done;  
 
b)  to provide a basis for accurate pricing and tendering;  
 
c) to serve as a comprehensive reference document for all part ies; 
 
d) to act as a reference if disputes arise or arbitration is necessary.  
 
6.2.2  Surface preparation  
 
For initial and factory painting, many substrates will benefit from specific surface treatments and preparation, 
which should be discussed with the coating manufacturer.  
 
The nature and extent of preparatory work should be specified as clearly as possible because of its influence 
on costs, appearance and subsequent performance. Imprecise terms such as "thoroughly prepare" or "burn 
off where necessary" , without further qualification, should be avoided (see 11.5.2.1). In circumstances where 
it is difficult to describe the standard of preparation to be achieved, for tendering purposes, a sample area 
should be prepared as an indication of the standard requ ired. 
 
Where a particular method of preparation is specified, it should be appropriate and relevant to the result 
required. For example, if a requirement to "remove all rust and scale by chipping, scraping and wire 
brushing" cannot be achieved (see 8.3.4.2 .4), the choice lies between selecting a more effective method or 
accepting a lower standard of preparation which will lead to a shorter life expectancy for the coating system.  
 
6.2.3  Coating system materials  
 
All the materials in a coating system should, if possible, be obtained from the same manufacturer. Where 
differing makes or brands are specified, a check should be made to ensure they are compatible (see 7.3.5). 
Materials should be used strictly in accordance with the manufacturer's instructions, incl uding guidance on 
whether thinning is permissible (see F.3.1). For work of modest size or where relatively few finishes or 
colours are to be used, information identifying different coating systems with particular areas should be 
incorporated in the specifi cation (see also 6.4).  
 
6.2.4  Application  
The specification should clearly state if circumstances require or preclude the use of particular methods of 
application and should indicate any requirements or constraints in respect of the conditions under which 
work is to be carried out or, if necessary, suspended, e.g. temperature, humidity, climatic conditions or other 
factors (see 9.1 and 11.4).   
50  © KEBS 2018 — All rights reserved   
6.2.5  Inspection procedure  
 
Where the work is to be subject to inspection, the intended inspection procedure should  be described in the 
specification (see 5.10).  
 
6.3 Bills of quantities  
 
Bills of quantities should be prepared in accordance with a document such as Code of procedure for the 
measurement of building work SMM7 measurement code [14]. It is essential that the relevant edition, or any 
other method of measurement adopted, is stated.  
 
6.4 Schedules  
 
For large or more complex projects, the preparation of a painting schedule, detailing location, nature of 
substrate, coating sys tem and (where relevant) colour  is recommended.  
 
A painting schedule should not be regarded as a substitute for the painting specification; site personnel 
responsible for supervision should have copies of both documents.  
 
6.5 Drawings  
 
Drawings should be used for large projects either for tendering purposes or as an aid to the organization and 
control of work.  
 
6.6 Records  
 
Painting and decorating work is usually carried out at regular intervals as a part of an overall maintenance 
schedule and so a planned approach is essential. Planning is  dependent on availability of information, and 
therefore, where expenditure on maintenance painting is significant, accurate records should be maintained.  
 
The essential information to be recorded includes dimensions, details of initial and maintenance co ating 
systems (including preparation) and costs. Other relevant information might include the conditions (e.g. 
weather, atmosphere or exposure conditions), methods of application employed, size of labour force and any 
special difficulties or problems encou ntered.  
 
 When work is subject to independent inspection during application, the inspection reports should be retained 
as a permanent record. Similarly, where a system of regular inspection of paintwork is in operation, as 
recommended in Clause 11, any obs ervations should be recorded. Apart from its contribution to ease and 
economy of maintenance, a system of recording can assist in the investigation of failures and the settlement 
of disputes.  
 
7  Materials  
 
7.1 Functions of coatings  
 
7.1.1   General  
 
In situations where the requirements of coating systems are specialized, the advice of a consultant or 
experienced paint manufacturer should be sought.  
 
7.1.2  Protection by coating systems  
 
The level of protection the coating systems can offer depends upon th e ability of the coating to prevent 
moisture, atmospheric pollutants, aggressive chemicals or other destructive elements coming into direct 
contact with the surface. The effectiveness of the coating depends upon its composition, especially its 
thickness, a nd the severity of attack. Where possible, particularly in severe conditions, consideration should 
be given to reducing dependence on the protective properties of coatings, e.g. by using less vulnerable 
building materials, by modifying the design of compon ents or by environmental changes such as improved 
ventilation (see 4.6.2).  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    51  
7.1.3  Decoration  
 
Even where the main emphasis is on protection or some other function, coatings should contribute to the 
overall appearance and decorative effect of buildings; in many instances, paint is the main decorative 
medium, providing the desired colours and degree of gloss or texture.  
 
Paint colours and their coordination with those of other elements in the decorative scheme, such as 
furnishing fabrics, floor coverings, lam inated and ceramic goods, is important and should be selected in 
accordance with the overall design specification.  
 
7.1.4  Hygiene  
 
Where specified, the coating should have the ability to withstand regular cleaning; where high standards of 
hygiene or steril e conditions have to be maintained, this might be the most important function. The coating 
should be of a type that resists not only the soiling agent but also the cleaning agent and method used.  
 
In situations favourable to the development of mould or bac terial growths, coatings having anti - microbial 
properties can be helpful, although too much reliance should not be placed on the ability of coatings alone to 
prevent mould or bacterial growth and, where possible, they should be supplemented by other measu res as 
described in 4.6.4.4.  
 
7.1.5  Special functions  
 
The coatings should be selected so that they are appropriate to the conditions of their use, e.g. of resistance 
to high humidity or direct chemical attack, reduction of fire hazard including surface sp read of flame and 
inhibition of mould or bacterial growth (see 4.6.4).  
 
7.2 General properties of coatings  
 
7.2.1  General  
 
Most of the coatings used on buildings pass from a wet stage to a dry film. Properties during the wet stage 
are described by terms such as viscosity, rheology, etc. and will have a direct influence on the application 
properties, flow and the final film thi ckness of the dry film. Coatings should therefore be selected according 
to the exposure conditions in which they are to be used  
 
7.2.2  Viscosity  
 
For most coatings, viscosity is the resistance offered by the material to shearing forces, e.g. brushing or 
rolling, and, consequently, directly affects the ease with which the material can be applied. Indirectly, it can 
influence film thickness because, if the viscosity is low, the coating can be spread out too far, yielding an 
excessively thin film. If it is to o high, it can be difficult to apply the coating in a film of uniform thickness, 
especially by brush.  
 
Application properties cannot always be  assessed either  from  the  apparent consistency of  the material in 
the container or by stirring or pouring, be cause of the effect of thixotropic and other Theological effects (see 
7.2.3).  
 
7.2.3  Flow  
 
Although good flow is a desirable attribute in a finish, excessive flow can make the material difficult to control 
hi application and cause running and sagging, ther efore, flow properties should be determined before work 
commences. Coatings with good flow tend to recede from external angles and sharp edges, reducing the 
thickness and protective value of the film at these points. In these circumstances primers and unde rcoats 
should be used as they are usually formulated to flow less freely than finishes.  
 
NOTE The consequences of poor flow are uneven film thickness such as with thin areas (e.g. brush -marks, spray mottle) that are 
below the average film thickness. These will confer less protection to the substrate. Poor flow will also adversely affect the reflectance 
properties and in gloss paint show poor distinctness of image.   
52  © KEBS 2018 — All rights reserved   
7.2.4  Film thickness  
 
NOTE  1 Film thickness is determined essentially by the proportion of no n-volatile solids (e.g. pigment or resin) present in the coating 
and its flow characteristics.  
 
The method of application should be considered as it can affect film thickness (see 9.3), and the protective 
properties of a coating are generally in direct pro portion to its film thickness which can also influence the 
filling and levelling properties.  
 
NOTE  2 Film thickness can be expressed as wet, i.e. the thickness immediately after application, or dry when the volatile constituen ts 
have evaporated. Dry film t hickness is the significant factor in relation to protection and filling properties.  
 
Most coatings have a build determined by the application and other characteristics. For most general 
purpose building paints, this should be in the order of 20 um to 35 um per coat dry film thickness.  Some 
special purpose coatings, such as low -build wood stains or two -pack pre -treatment primers, should have dry 
film thicknesses of 10 um or less. In addition, depending on type, high -build coatings can yield films in the 
range 60 um to 3 mm (e.g. textured masonry paints), although 100 um to 250  are more typical.  
 
7.3 Components of coating systems  
 
7.3.1  General  
 
A coating system comprises at least two coats either of the same material or a sequence of coats of differing 
type (e.g. primer, undercoat, finish, as described in 7.3.2 to 7.3.4). Coats should be selected according to the 
type of surface to which it will be applied and the nature and function of the coating required. Where the 
coating system provides a protective  function, more than two coats might be required. Where the coating 
system consists of a sequence of coats of differing type, the compatibility of the individual coats (see 7.3.5) 
should be taken into account in the selection of coats.  
 
7.3.2  Primers and s ealers  
 
An essential function of a primer is to secure good adhesion to the surface to which it is applied and, in turn, 
to provide a base to which the succeeding coats will adhere; other functions might include:  
 
a) the prevention of undue absorption of b inder from the subsequent coats,  leaving  them under bound 
or lacking in gloss on absorbent surfaces, such as wood, lightweight blocks, plaster and many building 
boards;  
 
b) the penetration of porous substrates such as wood and masonry to improve adhesion  and other 
performance factors;  
 
c) the inhibition of corrosion on metal, especially iron and steel;  
 
d) a reduction of the risk of attack on subsequent coats on surfaces of an alkaline nature, such as 
concrete, cement rendering, asbestos -cement and some t ypes of plaster;  
 
e) the provision of protection in the interval between erection or fixing and application of  the complete 
coating system on new wood, metal and other materials exposed to attack by moisture or other adverse 
elements.  
 
NOTE 1 Sealer is a term often loosely applied to coatings which might combine some of the functions of primers described in a) to d) 
with other functions, or which might be used for purposes other than priming.  
 
Examples include:  
 
— aluminium -pigmented primers that can be use d as wood primers and also as sealers for bituminous 
surfaces other than wood (see 8.15);  
 
— primer -sealers for powdery or friable surfaces (see 11.5.5) or for plaster and similar surfaces of high 
or variable porosity (see 8.6.2.4);  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    53 — protective coatings, usually unpigmented, e.g. clear sealers for metal sprayed steel (see 8.4 -1.2) and 
some multi - coloured finishes (see Table 7).  
 
NOTE 2  Well-thinned first coats of water -borne paint might be needed on plaster of high or variable porosity (see 8.6.2.4). The se are 
sometimes referred to as sealing or mist coats.  
 
7.3.3  Undercoats  
 
The essential function of undercoats is to provide a uniformly opaque base of a colour appropriate to that of 
the finish, but they also contribute to the thickness, filling properties and cohesion of the paint system.  
 
Manufacturer's recommendations regarding the use of undercoats should be observed. In some 
circumstances, undercoats might not be needed, or can be replaced in part by additional coats of finish. 
Many solvent -borne matt or mid -sheen finishes, for example, can be applied direct without undercoats to 
primed or previously painted surfaces. Solvent -borne gloss finishes are usually applied over undercoats, but 
in three -coat systems on primed or previously painted sur faces, with the manufacturer's approval, a system 
of one undercoat and two coats of gloss finish should be used in preference to two undercoats and one coat 
of finish, for greater durability externally or in severe internal exposure conditions.  
 
NOTE  Some manufacturers may restrict the use of general purpose undercoats to interior use, and will have more specific 
proprietary materials for external use.  
 
7.3.4  Finishes  
 
The finish is the final coat in the system and should be selected to provide the required  colour, degree of 
gloss, texture or other attributes, including resistance to weather, chemical attack and mechanical damage. 
In this respect, the finish is the most important coat in the system since its appearance and performance in 
service are frequent ly the criteria by which the coating system as a whole is judged. However, the finish 
should not be used to compensate for deficiencies in preceding coats in the system, whether these relate to 
quality, suitability or application.  
 
7.3.5  Compatibility of c oatings  
 
It is essential that the individual coats in the system are mutually compatible. Compatibility is influenced 
mainly by the composition and physical properties of each of the coatings in the system and, to some 
degree, by their juxtaposition and ag e. Incompatibility can be a cause of poor adhesion between coats in a 
system.  
 
NOTE   For example, a coating based on a solution binder (see F.2.5) might be unsuitable for use over a drying -oil/resin type coating, 
because its solvents can soften or disrupt the latter, although no problem might arise if the sequence of coats is reversed. Similarly, 
application of a hard coating over a softer one can result in cracking of the composite film while application of the softer coating over the 
harder one can be sat isfactory.  
 
Compatibility problems are less likely to arise with systems comprising coatings of similar composition and 
properties but, even with these, slight variations in the same types of coatings from different manufacturers 
can adversely affect the p erformance of the system. It is advisable, therefore, to ensure that all the coatings 
in a system are from the same manufacturer and are used in accordance with the manufacturer's 
recommendations regarding the sequence and number of coats.  
 
 
 
7.4 Ancillary  materials  
 
7.4.1  Cleaning agents  
 
Surface cleanliness is essential to the performance of coating systems. Detergent solutions or sugar soap 
are usually adequate for normally soiled surfaces. All residues should be completely removed prior to 
applying the coating system. For removal of oil or grease, proprietary solvent -emulsion cleaners should be 
used (see 11.5.3).  
 
7.4.2  Sterilizing washes   
54  © KEBS 2018 — All rights reserved   
Surfaces contaminated with mould or algal growths should be treated before coatings are applied. 
Household bleach so lutions are often effective in killing the growths but, in severe cases, proprietary mould -
inhibitive washes provide a measure of protection against their reappearance (see 11.5.8). All residues, 
including chemicals and dead mould/algal spores should be co mpletely removed prior to applying the 
coating system.  
 
7.4.3  Knotting  
 
Sealers should be used to hold back resin, tannin and other stains, which could discolour wood coatings on 
some wood species (see 8.1.1). The problem is most acute with white water -borne finishes.  
 
NOTE  The most common problems are associated with knots in the wood. Traditional sealers based on shellac solutions are known 
as knotting.  
 
Where knotting is used to retard discoloration of light -coloured opaque finishes, a quick -drying solut ion e.g. 
of shellac in industrial methylated spirit should be applied to knots or resinous areas in wood before priming. 
Two coats are more effective than one, however, knotting is not likely to be completely effective in cases of 
resin exudation.  
 
7.4.4  Stoppers and fillers  
 
7.4.4.1  General  
 
The distinction between stoppers and fillers has become less clear -cut with the widespread use of 
proprietary materials, many of which, although described as fillers, are used for both purposes. More 
meaningfully, the  materials might be categorized as stoppers, general purpose stoppers/fillers and surface 
fillers. Methods of stopping and filling are described in 9.2.4.  
 
7.4.4.2  General purpose stoppers/fillers  
 
General purpose stoppers/fillers are usually water -mixed and comprise the following.  
 
a) Powder fillers. These are supplied in powder form for mixing with water and are usually based on 
water -soluble cellulose and gypsum or white Portland cement. Those containing gypsum are suitable for 
general use as stoppers a nd fillers in dry interior situations.  
 
b) Water -borne fillers. These are usually based on vinyl or acrylic resin dispersions and are supplied in 
paste form, ready for use. Materials of this type vary considerably in characteristics and usage.  
 
Powder fill ers are not usually suitable for use for external work, especially on wood, but the manufacturer's 
recommendations in this respect should be observed. Portland cement types are suitable for external use on 
masonry surfaces and should not be used on woodwor k. 
 
Where water -borne fillers are used the manufacturer's recommendations, especially regarding suitability for 
exterior use, should be observed. It should be noted that some exterior grades contain coarse particles, 
making the attainment of a fine finish difficult. Linseed oil putty should not be used as a stopper.  
 
For stopping deep holes in woodwork, proprietary materials based on two -pack polyester or epoxy resins 
can give good performance but it is essential to use a grade supplied specifically for use  on wood.  
 
7.4.4.3  Surface fillers  
 
Surface fillers formulated specifically for use on timber are preferred to the general purpose types when a 
high standard of finish is required, especially with solvent -borne paint systems. They are supplied ready for 
use as smooth, finely ground, creamy pastes, and should be applied with a wide filling knife or spatula. The 
types in general use are water -borne, but solvent -borne formulations are also available.  
 
7.4.5  Mastics and sealants  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    55 Mastics and sealants are mainl y used for the repair or replacement of external pointing between window or 
doorframes and adjacent masonry. They do not need to be over -painted, except for one - pack, non -elastic 
types, which should be over -painted. Silicone mastics and sealants should no t be over -painted.  
 
7.4.6  Water repellants  
 
Water repellent solutions should be used when rain penetration of walls has caused internal dampness.  
 
8 Substrates and coating systems  
 
NOTE 1   Although concerned essentially with new work, surfaces that might n ot have been painted initially, such as external masonry 
or non -ferrous metal, come within the scope of this clause. Maintenance treatment is described in Clause 11, but much of the 
information given here is relevant.  
 
NOTE 2  The coatings referred to in this clause are generally those of conventional type, as defined in A.2 and described in Tables 12 
to 18, but 4.6.4 describes some functions and situations for which specialist coatings (see A.3 and Table 10) or modified con ventional 
coatings might be nece ssary.  
 
8.1 Wood  
 
8.1.1  Extractive  
 
8.1.1.1  General  
 
The potential for extractives to cause problems should be taken into account during the preparation of wood 
for coating. Wood material contains typically 5% to 20% of soluble material (see F.2.5). Extractives confer 
desirable properties such as durability and colour to wood, but they may also disrupt or discolour surface 
coatings.  
Extractives are manifested both as resins and in the form of soluble staining chemicals such as tannin.  Knots 
often cont ain a disproportional high percentage of resin and extractives, which can cause localized 
discoloration and physical disruption of paint. These problems should be alleviated through the application of 
a knot treatment or use of a purpose -designed stain -blocking primer (see also 7.4.3 and C.2.8).  
 
8.1.1.2  Resinous and oily materials  
 
Some hardwoods (e.g. gurjun, keruing and agba), and occasionally resinous pines (see C.2.5) contain a high 
content of resin distributed through the wood, which can give rise to  severe exudation problems. Kiln drying 
reduces the activity of resin in potentially troublesome timber but when resin content is very high, exudation 
can continue for long periods, especially on external woodwork exposed to the sun. In such situations, da rk 
coloured paints should be avoided.  
 
Other woods, such as teak and some cedars, contain oil, which can impair the drying, hardening or adhesion 
of coatings. These woods should be washed down with methylated spirits immediately before priming or 
varnishin g. However, they can usually be painted satisfactorily if an aluminium primer (3/5) is used.  
 
8.1.1.3  Tannin and other extractives  
 
Some species, notably Western red cedar and sequioa among the softwoods, and among hardwoods oak 
and chestnut, contain a re latively high level of tannins distributed throughout the wood. When finishing using 
a water -borne paint, a primer possessing stain -blocking properties should be used.  
 
Wood species containing high levels of tannins react with iron to produce strong blue -black discoloration. 
Contact with steel tools should be minimized, non -ferrous fixings should be used, and under no 
circumstances should smoothing be carried out using steel wool.  
 
8.1.2  Moisture content  
 
Wood should be painted or varnished when its moisture content is near to that at which it will stabilize in 
service, generally 15 % to 19 %, but lower in buildings which are heated continuously, typically 9 % to 11 %.  
  
56  © KEBS 2018 — All rights reserved  NOTE  Excessively dry timber swells as it takes up moisture (see C.2.3), imposing stresses on the coating; damp timber shrinks 
during drying, causing joints to open, creating further points for water to enter. Also, blistering or flaking of the surface  coating is likely to 
occur on damp timber.  
 
8.1.3  Penetration of binder  
 
Deep penetra tion is not necessary for priming coats to adhere and can be both wasteful of material and 
detrimental to performance as binder can be preferentially absorbed, leaving the dried film under bound or 
weakened.  
 
The large pores in hardwoods could be bridged b y paint coatings, leaving an air space beneath the film and 
forming a weak point that can initiate breakdown. To prevent this, filling should be undertaken when 
hardwoods are painted.  
 
Ease of penetration of liquid (see C.2.4) should be taken into account before using preservative treatment  
 
8.1.4  External influences  
 
8.1.4.1  Moisture  
 
The water -excluding efficiency of a wood coating is an important property that determines the extent of 
dimensional movement of coated wood in service, as well as influencing the risk of fungal decay. It should 
therefore be taken into account when selecting or specifying wood -coatings.  
 
Multi -coat, high -build coating systems are reasonably effective barriers to the free movement of liquid 
moisture and vapour provide d the coating is continuous and remains intact. However, all coatings allow 
some passage of water during wetting and drying, and this leads to consequent movement of the wood. 
Coatings should be selected that relate to the expected end -use category. Thus h ighly permeably wood 
stains are suitable for fencing where free movement is acceptable. A less permeable coating is  required for  
window joinery  where movement should  be  controlled. For  cladding an intermediate level of permeability 
is acceptable.  
 
Moisture could gain entry through open joints, defective putties and sealants, and the paint film might then 
hold the water in. In jointed components the principal route for moisture entry is through end grain concealed 
within the joints. Components that hav e their end grains sealed during manufacture should be selected 
where the reduction of wetting and the improvement in coating performance is desirable.  
 
Moisture movement places a cyclic strain on the coating system that may eventually result in cracking. Some 
coating formulations offer higher film flexibility and should be used where good exterior durability is 
necessary. The use of such coating in no way reduces the need for good design and an appropriate 
preservative treatment should still be used.  
 
8.1.4.2  Weathering  
 
NOTE On external exposure to sun and rain, unprotected wood loses its original colour and the surface 
degrades until it consists of a thin layer of loosely matted fibres, usually dirt -stained and darkened by fungal 
blue stain and iron stai ning. After periodic wetting and drying, the growth rings can become prominent and 
splitting and distortion can occur.  
 
If it is desired to preserve the natural appearance of external woodwork, protective surface treatment is 
essential (see Table 9). Denatured wood should be removed back to a sound wood surface before 
application of a coating as weather -degraded wood is a very poor substrate. Even when wood is not 
obviously degraded, the paint holding properties could be severely compromised. Wood shou ld therefore be 
protected from the elements, and for exterior exposure, will benefit from a penetrating treatment as the first 
coat of any coating system.  
 
Solar heat gain causes shrinkage of wood and consequent cracking and opening of joints; it can also 
increase resin exudation, resulting in discoloration and disruption of coatings. Dark finishes should be 
avoided as they exacerbate this.  
 
8.1.4.3   Fungal attack  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    57  
NOTE Wood, which is not naturally resistant, is susceptible to fungal attack if its moisture content exceeds a mass fraction of about 
22 % for lengthy periods. In painted woodwork, the principal agents of decay are the wet -rot fungi. Surface moulds and blue -stain fungi 
have little effect on the durability of timber although they are unsightly and can disfigure paintwork. Exterior timbers  not  in  contact  with  
the  ground are  unlikely to rot if they are of moderately durable species  or  better,  but this classification applies only  to the heartwood; 
all sapwood is vulnerable to decay.  
 
Where ti mbers of a lower durability rating are used, or if appreciable quantities of sapwood are present, 
application of a preservative, where practicable by impregnation, should be undertaken to prevent fungal 
attack  
 
8.1.5  Preservative treatments  
 
Provided adequate drying of the treated wood is allowed prior to painting, preservation will not give rise to 
any adverse effects on paint performance. Preservative treatment of timber according to species, end use 
and desired service life should be in accordance w ith BS 8417 and BS 5589. The treatment of components, 
e.g. window joinery, which are to be subsequently coated should be as follows.  
 
a) Treatments for window joinery and other external building timbers not in ground contact:  
 
1) Copper -based preservative formulations which are chromium and arsenic free can be used, 
but the long term performance of these formulations is not fully established by field trials.  
 
2) Organic solvent and micro -emulsion preservatives, e.g. conforming to BS 5707 and water - 
repellen t types, containing waxes or resins, suitable for painting, can be used. These types of 
preservatives can be applied by immersion or the double vacuum process as specified in BS 5707. 
Application by brushing or spraying is not recommended except for site t reatment of cut ends etc., or 
in remedial work. These preservatives are generally suitable for over - painting provided a  minimum 
of  48  h in  conditions of  good ventilation is  allowed for evaporation of solvent, but users should 
satisfy themselves as t o the compatibility of the particular treatment with the coating system to be 
applied.  
 
3) Diffusion treatment with disodium octoborate . This treatment can be carried out on freshly 
felled timber and can be applied to seasoned timber. The salts remain  wa ter-soluble and  can  affect 
coatings if  the  timber becomes wet  although, in practice, few difficulties appear to arise.  
 
b) Treatments for fencing and gates in or out of ground contact:  
 
Application of preservatives by brush is a less effective means of conferring resistance to biological attack 
than impregnation, because penetration of the fluid is limited and the protective zone relatively shallow. 
Nevertheless brush application should be used for treatment of component repairs prior to painting, and  also 
in conferring resistance to blue stain disfigurement of paints and stains. Clear preservative primers are 
available, usually of solvent -borne type, which contain resin in addition to fungicide and serve to stabilize the 
wood surface and improve the p erformance of the coating system. They should be applied liberally, 
particularly over end -grain surfaces.  
Preservatives are also a useful adjunct in prior -to-painting repairs on external timber components. After 
remedy of defective timber using resin repai r or traditional methods of timber inserts, wood which is sound 
but deemed to be vulnerable to decay should be protected by the insertion of preservative plugs to provide a 
latent reserve of fungicide.  
 
8.1.6  Surface preparation, priming, stopping and fill ing 
 
8.1.6.1 General  
 
The moisture content of the timber should be measured before painting and should not exceed the expected 
equilibrium value (see 8.1.2). An electrical moisture meter with long probes should be used so that readings 
can be taken at a de pth not so readily affected by surface drying.  
  
58  © KEBS 2018 — All rights reserved  NOTE   Moisture content can be measured with sufficient accuracy for painting purposes with an el ectrical 
moisture meter of the conductive type. Electrical  moisture meters  can  give  a  falsely  high  readin g  if  
soluble  salts  are  present,  e.g.  from preservative treatment with disodium octoborate.  
 
If there is a delay between delivery to site and fixing or erecting of joinery, it should be protected against 
ingress of moisture (see 5.7).  
 
If limber has received preservative treatment, time should be allowed for drying out or evaporation of solvent 
before priming (see 8.1.4).  
 
8.1.6.2   Surface preparation  
 
8.1.6.2.1  General  
 
Preparatory treatment of wood should be undertaken before priming, e.g. cleaning,  abrasion and treatment 
of knots. Thorough surface preparation is especially important on wood that has been exposed to weather 
without protection.  
 
8.1.6.2.2   Cleaning  
 
A clean surface is essential to the satisfactory adhesion and appearance of the paint system. Dirt and 
surface deposits, exuded resin and soluble salts arising from preservative treatment should be removed. If 
the surface is contaminated with oil or grease, solvent cleaning may be necessary (see 7.4.1).  
 
8.1.6.2.3  Abrasion  
 
Where necessary, abrasion should be used to clean the surface, reduce roughness and improve paint 
adhesion.  
 
Wood can be sanded mechanically or manually using traditional glass paper or one of the more modern 
abrasive pads with incorporated grits. It is essentia l to use a grade of abrasive paper appropriate to the 
surface; excessively coarse grades can damage the wood fibres, impairing the appearance and possibly the 
performance of the paint system. The surface should be sanded in the direction of, and not across , the grain 
without using excessive pressure, which can damage the wood fibres. Care should be taken not to damage 
moulding and arris edges.  
 
Steel wool should not be used on unpainted joinery as it may leave tiny particles of wire which can rust and 
spoil the finish.  
 
Surface preparation is particularly important for weather -degraded wood, and is best achieved by planing or 
mechanical sanding. An effective alternative is scraping the wetted denatured surface, followed when dry by 
thorough abrasion, and the  application of a transparent preservative primer (e.g. 3/6).  
 
8.1.6.2.4   Knot treatment  
 
Discoloration of paint, especially noticeable with light colours, can occur over knots and resinous areas 
especially if the wood has been treated with preservative co ntaining certain organic solvents (see 8.1.5 and 
C.2.7). Discoloration may be minimized by the application of a knot treatment, e.g. knotting (see 7.4.3).  
Heavy applications and the use of knotting which has thickened through evaporation of solvent should be 
avoided; otherwise paint adhesion can be impaired. Knotting should not be used if finishing with semi -
transparent wood stains.  
 
In severe instances of resin exudation from knots, the knot may be removed by drilling, followed by filling of 
the hole.  
 
8.1.6.3  Priming  
 
Note  Primers for wood are listed and described in Table 3, and typical applications are indicated in Table 12 and Table 13.  
 
A good primer, applied to dry sound substrates, is the foundation of a durable paint system. Using 
components primed  in the factory or works is recommended but if site priming is necessary, it should be KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    59 carried out immediately after delivery of the joinery, provided that its moisture content is at an appropriate 
level (see 8.1.2). Although single coats of primer retard surface degradation by sunlight (see 8.1.4.2), they 
provide only limited protection against moisture, (especially if the wood has not been treated with a water -
repellent preservative) and therefore the full system should be applied as soon as possible. Pri med joinery, if 
not fixed or erected immediately, should be properly stored (see 5.7).  
 
If pruned woodwork has been exposed for a lengthy period, the condition of the primer should be checked 
before continuing application of the paint system. It is importa nt that areas of defective or poorly adhering 
primer be removed and the exposed areas reprimed. If the primer is firmly adhering but is chalking or 
powdery, it should be lightly abraded and a further coat applied.  
 
8.1.6.4  Stopping and filling  
 
Note  Mater ials used for stopping and filling are described in 7.4.4 and the techniques are described in 9.2.4.  
 
Drying -oil/resin stoppers and fillers should be used only on primed surfaces; otherwise oil is absorbed 
leaving the material underbound.  
 
8.1.7  Coating systems for interior use  
 
NOTE   For information on coating systems for interior wood, see Table 8 and Table 12.  
 
8.1.7.1  Solvent -borne paints  
 
Internal use of solvent -borne paints should be restricted because of increasing environmental and legislative 
pressures aimed at eliminating health risks to painters and reducing volatile organic compounds (VOCs).  
 
Note:  The traditional solvent -borne system consists of three -coat application: primer, undercoat and gloss 
finish. However, mid -sheen and matt finish sol vent-borne paints are sometimes applied coat -on-coat, or as 
two coats over the primed wood.  
 
If it is necessary to capitalize on the speed of drying of the water -borne systems, water -borne primers and 
primer/undercoats should be employed under the final gl oss finish.  
 
8.1.7.2   Water -borne paints  
 
Water -borne paints should be applied using synthetic filament rather than natural bristle brushes as the 
synthetic filament aids the flow of the coating material and reduces brush -marking.Before the application of 
water -borne paints, bare wood knots should be sealed to reduce the risk of tannin staining (see 8.1.1.1).  
 
8.1.8  Coating systems for exterior use  
 
Note: For information on coating systems for exterior wood, see Table 9 and Table 13.  
 
8.1.8.1  General  
 
Coating systems for exterior use should provide a flexible weather -resistant coating that maintains its 
integrity and protective effectiveness in the long term.  
 
8.1.8.2  Paint systems  
 
8.1.8.2.1 Solvent -borne exterior paints  
 
NOTE  Solvent -borne exterior paints are generally based on flexible alkyd resins and are available in a 
range of sheen levels. They generally adopt the traditional system approach of primer, undercoat and gloss, 
though in some low -sheen materials one product is applied in two coats ov er a primer, or even as three 
coats on bare wood. Solvent -borne exterior alkyd paints possess superior durability to general -purpose 
alkyds, but nevertheless lose flexibility during weathering. Solvent -borne exterior paints can be used over 
water -borne pri mers (see BS 7956).  
  
60  © KEBS 2018 — All rights reserved  Solvent -borne exterior paints should be used when a high quality appearance and a more tolerant 
application under adverse weather conditions is necessary.  
 
8.1.8.2.2  Water -borne paints  
 
NOTE 1 Water -borne paints possess a range of app lication benefits associated with the use of water as solvent -carrier, for example 
low-odour, low -VOC content, ease of clean -up and non -flammability.  
 
Water -borne paints can be formulated to give high performance coatings for exterior wood and should be 
applied at a spreading rate in accordance with the manufacturer's recommendations to provide appropriate 
film thickness and so ensure long -term durability. Water -borne paints offer less resistance to being over -
brushed and minimum film thicknesses should b e specified.  
 
NOTE 2  Initial gloss and flow properties of water -borne paints are presently inferior to those of solvent -borne alkyds. Cold, damp 
exterior conditions can affect the application of these products.  
 
8.1.8.3  Solvent -borne and water -borne exter ior wood stains  
 
Clear varnishes (9/1, 9/2) perform very poorly on exterior wood in exposed situations and should not be used 
unless frequent maintenance is acceptable. Exterior high -build wood stains should be used on exterior wood 
as they contain resinou s binders to resist moisture movement, pigments and ultraviolet absorbers to protect 
against degradation by sunlight, and often biocides to protect against fungal discoloration.  
 
NOTE  Modern exterior wood stains can be of solvent -borne or water -borne type , and are carefully formulated compositions 
designed to provide comprehensive protection to the wood under demanding conditions.  
 
Low-build exterior wood stains should not be used for components such as exterior joinery where 
dimensional control is importa nt (see 8.1.4).  
 
Low-build stains should be used on components for which dimensional movement is to be expected, such as 
cladding, bargeboards, gates, fences, etc., and which often have a sawn finish.  
 
NOTE  The moisture permeability of the wood stain is un likely to give rise to problems, though cladding 
which has been poorly fixed (without a movement allowance) or installed at an inappropriate moisture 
content can distort.  
 
It is essential that maintenance of medium -build wood stains be carried out before a ny loss of film integrity, 
because any exposure of the wood to weathering can result in discoloration, which no semi - transparent 
coating can disguise.  
 
8.1.9  Flame -retardant treatments  
 
8.1.9.1 General  
Materials, either surface or impregnation treated, should be kiln dried to a maximum moisture content of 12% 
before application of a decorative coating system. It is important that the surface of the treated material is 
clean and dust free. Chemical or other surface deposits should be removed by light sand ing. 
 
Treated materials can be painted with clear, pigmented and opaque products, using conventional methods of 
application, but the manufacturer's recommendations should be observed. It is essential to establish that any 
coatings do not adversely affect t he spread of flame characteristics or the treated materials.  
 
Highly flammable coatings such as nitro -cellulose -based lacquers that can contribute to the risk of flame 
spread, should not be used.  
 
Care should be taken when applying a decorative coating to flame -retarded substrates that the flame - 
retardant properties are not degraded. Advice on painting over flame -retardant treated materials should be 
sought from the manufacturer.  
 
8.1.9.2  Inorganic flame retardants  
 
Inorganic flame -retardant treated mater ials should be protected at all tunes from the elements, both at the 
treatment plant and on site.  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    61  
The flame -retardant treated material should receive at least the first coat of the coating system as soon as 
possible and before installation.  
 
Providing the se recommendations are followed, the presence of the flame -retardant chemicals in the wood 
should not affect the performance of the paint film hi dry exposure conditions.  
 
8.1.9.3   Resin -based flame retardants  
 
Resin -based flame retardants should be kiln d ried after treatment, to cure the chemical within the timber.  
Note: Resin -based  flame  retardants  can  be  used  externally  or  can  be  subjected  to  high  humidity  
and  under  these conditions there is no loss of flame retardance or paint film integ rity. 
 
8.2 Wood -based panels products  
 
NOTE  For further information on wood -based panels, see Annex C.  
 
8.2.1  Characteristics  
 
8.2.1.1  Plywood  
 
Plywood for external use is manufactured with weatherproof adhesive but not necessarily with durable 
species of  timber throughout; if non -durable species are incorporated, preservative treatment should be 
applied (see 8.1.5).  
 
The outer layers of plywood exposed to weather are prone to develop checking (fine surface cracks, defined 
in BS 2015) running parallel to t he grain, even when painted. Plywood is available with a resin -impregnated 
paper overlay, which prevents checking and provides a satisfactory base for painting; the use of this type of 
material is recommended for external plywood cladding and similar appli cations when a paint finish is 
required, especially with species prone to severe checking. Exterior wood stains (see 8.1.8.3), especially 
those of the low -solids type, are less likely to give trouble and are more suitable than paint or varnish for use 
externally on plywood without a paper overlay. However, because of the low resistance of low -solids wood 
stains to water vapour, fluctuations in moisture content can result in water -soluble salts, present in the 
adhesive, being brought to the surface. These ar e normally removed by rain but, if the surface is sheltered 
from direct rainfall, a white deposit can build up and mar the appearance. The salts should be washed off but 
will reappear until they are depleted.  
 
8.2.1.2  Fibre building board, wood chipboard and plasterboard  
 
When it is necessary to paint fibre building board, wood chipboard and plasterboard the manufacturer's 
recommendations should be followed in respect of board types and design details.  
 
Where a reduction in the number of site applied coats  is necessary or a higher standard of finish is desired, 
fibre building boards and wood chipboards supplied with a factory -applied primer, sealer or surfacer on one 
or both faces should be selected.  
 
NOTE  C.3.1.2 describes the four main types and the typi cal treatment of fibre building board.  
 
8.2.1.3   Wood chipboard  
 
Like timber, chipboard can be attacked by wet -rot fungus if its moisture content is above the critical level for 
lengthy periods; the physical properties of the board can also be affected. Moisture -resistant grades are 
available for use in highly humid conditions and should be installed in accordance with manufacturer's 
recommendations regarding design detailing and fixing methods.  
 
NOTE  Preservative treatment, as recommended for wood in 8.1 .5, is not usually suitable for wood 
chipboard.  
  
62  © KEBS 2018 — All rights reserved  The natural surface of chipboard varies according to the method of spreading the chips during manufacture. 
If the surface has a coarse or open texture, it should be filled before painting to obtain a satisfactory finish. 
Some methods produce a surface of finer texture requiring little or no filling before painting.  
 
8.2.2   Preparation and coating systems  
 
8.2.2.1   Surface preparation  
 
Knots are rarely a problem on good -quality plywood, but any present should be treated with knotting before 
painting (see 8.1.6.2.4).  
 
Except with the more open -surface grades of wood chipboard (see 8.2.1.3), building boards do not usually 
need sanding before being painted. If sanding is considered necessary to improve adhe sion to glossy -
surfaced hardboards, a fine grade of abrasive paper should be used and care should be taken to avoid 
scoring the surface, as this can result in localized swelling along the score marks when paint is applied.  
 
Wood -wool surfaces should be cle aned with a stiff, but not wire, brush. Loose dust should be removed with a 
soft fibre brush or vacuum cleaner (the dust can be strongly alkaline).  
 
8.2.2.2  Stopping and filling  
 
If checking has occurred on external plywood and it is to be painted, it sho uld be filled after pruning. For 
stopping -up nail and screw holes and repairing minor damage to the surface, either water -mixed or drying -
oil/resin stoppers or fillers should be used.  
Water -mixed stoppers and fillers can be used on either primed or unprime d surfaces. On unprimed surfaces 
and on factory -pruned or sealed boards, exposed heads of nails and screws, unless they are rust -resistant, 
should be touched -in with quick -drying solvent -borne primer to prevent rust -staining. If a water -mixed 
material is u sed for stopping -up after priming or on factory -pruned or sealed boards, it might be necessary to 
touch -in the stopping with primer to ensure a surface of uniform absorption. Drying -ou/resin stoppers and 
fillers should be used only on primed or sealed surf aces.  
 
If a high standard of finish is desired on some types of wood chipboard, water -mixed or drying - oil/resin fillers 
can be used, but the surface should first be primed.  
 
Note:  Direct application of water -mixed fillers causes swelling of the wood chip s; with drying -oil/resin fillers, 
the binder is absorbed.  
 
8.2.2.3 Priming  
 
 
 
NOTE Primers for painting plywood are as described for wood in Table 3. Table 1 gives general guidance on the selection of 
primers.  
 
Varnish and wood stains are usually applied direct, but thinning of first coats might be necessary and the 
manufacturer's recommendations should be followed.  
 
If not primed or sealed during manufacture, building boards should be primed before application of solvent -
borne (e.g. alkyd) paint systems. Normal practice is to use primers of the types employed for wood  or  
plaster  (Table  3  and  Table  5),  but  any  specific  recommendations of  board  or  paint manufacturers 
should be followed.  
 
Except as indicated in Table 18, priming is not usually n eeded when water -borne coatings are to be applied 
to building boards. Priming of boards that have received flame -retardant treatment [see C.3.1.2, 4)] is 
recommended to prevent efflorescence or discoloration caused by reaction between water -borne coatings 
and chemicals used in the treatment. Similarly, priming of single layer wood chipboard might be necessary to 
prevent absorption of water and consequent swellings of the chips that produce a rough surface.  
 
Bitumen -impregnated insulating boards, if they are  to be painted with solvent -borne paints, should be primed 
with an aluminium primer or sealer to prevent discoloration (bleeding).  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    63 Traditional practice, especially with fibre building boards, is to prime or paint (back -prime) unexposed faces 
of boards to prevent absorption of moisture. In most circumstances, and provided that boards of appropriate 
types are installed in accordance with the manufacturer's recommendations, this is not necessary. Unless 
the board manufacturer advises otherwise, wood -based pan el products should not be back -primed.  
 
8.2.2.4   Finishing of internal work  
 
The types of coating systems indicated in 8.5.2 and 8.5.3 as suitable for use on plaster, should also be used 
on building boards.  
 
8.2.2.5  Finishing of external work  
 
NOTE 1 Coati ngs suitable for use on plywood are shown in Table 5 and Table 7.  
 
When installed in accordance with the supplier's recommendations, some types of hardboard and medium 
board are suitable for external use.  
 
Factory -applied treatments suitable for exterior e xposure are available but, when site painting is necessary, 
the types of coating systems (except cement paints) described in 8.5.3 as suitable for external surfaces 
should be used.  
 
NOTE 2 Typical coating systems for externally sited boards are indicated i n Table 13.  
 
On external cladding, it is recommended that vapour -permeable coatings should be used; textured coatings 
are particularly suitable. Selection of systems and their performance in service is, however, influenced by the 
materials and forms of con struction, and reference should be made to board and paint manufacturer's 
recommendations in specific circumstances.  
 
8.3   Iron and steel  
 
8.3.1  General  
 
The painting of the ferrous metal surfaces normally encountered in buildings, in moderate external and 
internal exposure conditions (see Table 2) may be undertaken using paints of conventional type. For a more 
comprehensive treatment of iron and steel, especially in situations where the exposure conditions are 
classified as severe, the areas are extensi ve or long -life painting systems are required, the painting should 
be in accordance with KS ISO 12944 for steel structures (and BS 5493 for iron structures).  
NOTE 1 Non-ferrous metals, notably zinc and aluminium, are frequently used as protective coatings on iron and steel, either alone or 
in conjunction with paints. Painting systems for metallic coatings are described in 8.4.  
 
NOTE 2 For further information on iron and steel, see Annex H.  
 
8.3.2  Characteristics  
 
8.3.2.1  Mild steel  
 
Hot-rolled mild steel bears a layer of millscale. Shedding of this millscale occurs before the steel has been 
painted, giving differences in electrical potential between the exposed surface and the surrounding adherent 
scale, corrosion cells can be created and result in severe attack on the bare steel. If the scale becomes 
detached after painting is completed, costly preparation and repainting is necessary. Millscale should be 
removed as described in 8.3.4 before the steel is painted; it is essential that this be done if high -durability or 
specialist coatings are to be applied.  
 
8.3.2.2 Stainless steel  
 
If painting  of  stainless  steel  is  necessary,  surfaces  should  be  abraded  and  degreased  before 
application of a pre -treatment primer.  
 
NOTE   Proprietary systems are avai lable for application to stainless steel (see Table 15).  
 
8.3.3  Design considerations   
64  © KEBS 2018 — All rights reserved   
The effectiveness of paints in protecting iron and steel can be increased, and the risks of corrosion 
diminished, by good design.  
 
KS ISO 12944 -3 and BS 5493 give detail ed guidance on designing for the prevention of corrosion, but the 
following aspects should be applied.  
 
a) All surfaces of exposed metal that need regular maintenance paint ing should be fully accessible. 
Surfaces such as back -to-back angle -iron trusses should be spaced far enough apart to permit painting or be 
treated with mastic or anti -corrosive paste before being butted together. Sealing gaps with gun, trowel or 
pouring grade sealants is an accepted method of protecting surfaces inaccessible for paint ing. Pipework, 
especially when sited externally, should be spaced from walls far enough to admit a paintbrush or paint 
glove.  
 
b) Drainage of trough sections should be arranged, e.g. by drilling holes, to prevent retention of water.  
This is especially imp ortant in salt -laden atmospheres. Water traps should be avoided where steel 
stanchions enter the ground or are embedded in a concrete base. Measures should be taken to prevent 
discharge of waste steam and liquids on to steelwork.  
 
c) Sharp, internal angles , crevices and cavities should be avoided or, if unavoidable, should be filled 
with weld metal or mastic.  
 
d) Electrochemical corrosion  can  occur  at  contact  surfaces  between  dissimilar  metals  in  the 
presence of an electrolyte, e.g. rainwater. If possible, direct contact should be prevented by measures such 
as placing plastic sheets between the contact surfaces or applying thick bituminous coatings to them. 
Alternatively, electrolyte should be excluded by making joints watertight and applying an im permeable 
coating.  
 
NOTE Rainwater run -off from copper to steel could also cause corrosion.  
 
8.3.4  Surface preparation and priming  
 
8.3.4.1  General  
 
The effectiveness with which millscale and rust are removed depends upon the method employed; the 
methods in general use are described in 8.3.4.2.1 to 8.3.4.2.5. Removal of oil, grease and dirt is also 
important. If iron and steel have been exposed to severe or very severe exposure conditions, e.g. marine 
and industrial, where residual surface contaminants can  stimulate corrosion, care should be taken in 
cleaning.  
 
The effectiveness of coating systems in protecting iron and steel is dependent upon the following factors.  
 
a) The nature and thoroughness of the preparatory method. The millscale and rust should be 
thoroughly removed to allow for an effective paint system to be applied. Preparatory methods are described 
in 8.3.4.2.  
 
b) The type of primer used. Generally, primers for iron and steel should contain corrosion -inhibitive 
pigments (see F.4.5). The choice o f primer is influenced by the preparatory method employed (see 8.3.4.2).  
 
c) The extent to which the system is able to exclude air and moisture. This is determined mainly by the 
total thickness of the paint film, its physical properties and the conditions of exposure (see Table 2). The 
minimum film thickness for satisfactory protection in moderate external exposure conditions is approximately 
125 um but films of 250 um or more might be required in severe exposure conditions.  
 
Whenever possible, steelwork sh ould be prepared and primed off -site; this usually compares favourably in 
cost and effectiveness with site treatment. When practicable, it is advantageous to apply off -site one or more 
of the subsequent coats in the coating system, although this might resu lt in divided responsibility for the 
work.  
 
8.3.4.2  Surface preparation  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    65 8.3.4.2.1   Abrasive blasting  
 
Note 1  This involves directing a stream of metal shot, grit or other abrasive particles at high velocity against 
the surface of the steel. The abrasive particles are propelled by compressed air or high -pressure water (or a 
combination of the two) or thrown by centrifugal force from an impeller wheel. For some purposes, high -
pressure water without abrasive particles can be used.  
 
Abrasive blasting is the m ost effective method of preparing steelwork for painting and is essential when 
specialist coatings are to be used, e.g. in severe and moderate exposure conditions. In respect of cost and 
effectiveness, blast -cleaning should be carried out under factory con ditions although the method is also 
suitable for the preparation of erected steelwork in some circumstances.  
 
In addition to its effectiveness in removing rust and millscale, abrasive blastin g provides a roughened surface 
which improves paint adhesion. Exc essive roughening, however, including the use of abrasive particles 
which are too coarse for the intended thickness of paint to be applied, can produce peaks which protrude 
through the paint film and form focal points for corrosion.  
Abrasive blasted surfac es are extremely vulnerable to corrosion (flash rusting) and should be primed as 
soon as possible and in any case within 4 h of cleaning, (see 8.3.4.3).  
 
8.3.4.2.2   Acid -pickling  
 
Acid-pickling is a factory process involving immersion of iron and steel in hot acid solutions to remove 
millscale and rust but might not provide a satisfactory base for some specialist coatings and therefore the 
coating manufacturer should be referred to for advice.  
 
For site treatment of steelwork, proprietary washes and pastes,  usually based on phosphoric acid should be 
used. They do not remove heavy rust or tightly adhering scale but can assist manual cleaning. Many types 
require washing -off; if this is not done properly, the performance of the paint can be affected and, if dry ing is 
slow, the steel will rust again. Washing -off water should not be allowed to run over adjacent brickwork or 
stonework. Where solutions claim to not require washing -off, the manufacturer's recommendations should be 
followed.  
 
8.3.4.2.3   Flame -cleaning  
 
Flame cleaning is not recommended and is more suitable for use in maintenance painting than in the initial 
treatment of new steel. It does not remove all rust and scale and should in no way substitute for abrasive 
blasting. It should not be used on thin sheets or on sections less than about 0.5 mm in thickness because of 
the risk of distortion, or on steel which has been coated with non -ferrous metals such as zinc and cadmium. 
Flame -cleaning might not provide a satisfactory base for some specialist coatin gs.Flame -cleaned steel 
should be primed while it is still dry and warm but not hot.  
 
8.3.4.2.4  Manual preparation  
 
NOTE 1 Manual preparation includes the preparation of iron and steel using hand or powered tools such as wire brushes, chipping 
hammers, chi sels, scrapers and vibratory -needle guns.  
 
Manual preparation is the least effective method of preparation and should not be used for steelwork 
exposed to severe or moderate conditions unless the size of the areas or other circumstances might 
preclude the use of more effective methods. Manual preparation does not provide a satisfactory base for 
specialist coatings and therefore especially formulated coatings, which are tolerant of poorly prepared 
surfaces, should be used.  
 
Manual preparation, whether with hand or power tools, is laborious and it is difficult to maintain a uniform 
standard for any length of time. Power tools usually give best results, but care should be taken to avoid 
surface damage such as burning, indentation, burring and scoring as peaks can be produced which protrude 
through the paint film and become focal points of corrosion. Over -vigorous brushing with hand or power tools 
should also be avoided as it can produce excessively burnished areas to which paint adhesion is poor.  
Weathering should not be employed as an alternative to more effective methods, such as abrasive blasting, 
in situations where complete removal of rust and scale is essential.  
  
66  © KEBS 2018 — All rights reserved  NOTE 2 Reliance is often placed on weathering (i.e. exposure to the elements) to loosen mil lscale sufficiently to permit its removal by 
manual cleaning. However, weathering to the point where all the millscale has loosened can take many months, and it is rarely  
practicable to allow time for this. It is also unlikely that all the surfaces weather  at the same rate, thus making it impossible to prepare 
the surface to a uniform standard. Also, in chemically polluted and marine atmospheres, lengthy exposure results in contamina tion of 
the surface and increased risk of corrosion.  
 
8.3.4.2.5   Removal of  oil, grease and surface deposits  
 
In factory processes, oil and grease should be removed with hot alkali solutions, solvent emulsions or 
solvents, followed by thorough rinsing with water, or by steam cleaning or high -pressure water jets. Where 
possible, t hese methods should be used on site, but often all that can be done is to wipe the surface with a 
proprietary cleaning agent and a succession of clean swabs, taking care to avoid spreading the oil or grease 
over the surface.  
 
Surfaces which are contaminate d following exposure in marine or chemically charged atmospheres should 
be washed with clean water, rinsed and allowed to dry before priming. Rust that develops as a result of 
washing should be removed.  
 
8.3.4.3  Priming  
 
NOTE 1  Table 4 lists and describe s the primers for iron and steel in general use in conjunction with undercoats and finishes of 
conventional use. Typical applications are shown in Table 14.  
 
Zinc-rich epoxy primers (4/8) can be over coated with most other coating types, including most spe cialist 
coatings. Advice should be sought from the coating manufacturer when drying -oil/resin coatings are to be 
used over zinc -rich primers.  
 
Primers  for  iron  and  steel  should  be  selected  according to  the  type  and  standard  of  surface 
prepara tion and the conditions of exposure, including the time that is likely to elapse between pruning and 
completion of painting.  
 
Abrasive blasting provides a satisfactory base for all types of primers. When less effective methods are 
employed, notably manual cleaning, more tolerant primers, e.g. 4/5, 4/8, or 4/10, should be used.  
 
NOTE 2 When steelwork is blast -cleaned in the factory it is usual to combine this treatment with application of a prefabrication primer, 
e.g. a zinc -rich epoxy type (4/8).  
 
It is essential that priming follow preparation as quickly as possible and certainly on the same day, otherwise 
further corrosion can develop. The interval between preparation and priming is especially critical with blast -
cleaned surfaces, and priming should fol low preferably within 1 h and certainly within 4 h; if it is likely to be 
delayed beyond this, a temporary protective or holding primer, e.g. 4/1 or 4/2, should be applied.  
 
Primed surfaces should be overcoated as soon as possible. If there is likely to be  a delay in applying further 
coats, the primer should be resistant to weathering and has to afford some protection to the surface. Most 
prefabrication primers and the tolerant types (see Table 4) can be left uncoated for a maximum of about 9 
months dependi ng upon the conditions of exposure and the effectiveness of the preparatory work. Other 
types of primers (including surface tolerant primers, i.e. 4/10, can be equally effective, but the manufacturer 
should be consulted on this aspect.  
 
Primed steelwork, e specially if it has been exposed for a lengthy period, should be examined carefully before 
further coats of paint are applied. If the primer has deteriorated, e.g. is perished, eroded or poorly adhering, 
or has been damaged, so allowing corrosion to develo p, the affected areas should be re -prepared and 
primed. If there is evidence of widespread corrosion beneath the primer, it should be removed and the 
surface again prepared and primed.  
 
Oil, grease and surface deposits should be removed from primed surfaces as desc ribed in 8.3.4.2.5. 
Removal of salt deposits by  washing from  surfaces pruned with zinc -rich primers is  especially important as 
the corrosion products formed by reaction between the salts and the zinc can affect the performance of 
subsequ ent coats.  
 
With a single coat of primer, it is difficult to obtain films of uniform thickness and free from pinholes, the 
points at which corrosion starts. In all but mild interior exposure conditions, two coats of primer should be 
applied. However, where  application of two coats cannot extend to the whole of the surface, a second coat KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    67 should be applied to vulnerable points, e.g. along external angles and to bolts and rivet heads (stripe 
coating). When a factory -applied prefabrication primer has been used and a paint system of conventional 
type is to be applied, the second coat should be either a zinc phosphate (4/5), chromate (4/8) or water -borne 
acrylic (4/9) or a two pack surface tolerant primer (4/10).  
 
8.3.4.4  Coating systems for interior and exterior  use 
 
8.3.4.4.1  General surfaces  
 
The number and type of coats applied after priming is determined by the protection and appearance 
requirements as well as by  the  properties  of  the  individual  coatings.  Generally,  the  combined thickness 
of priming  and finishes should be a minimum of approximately 125 µm for good protection in moderate 
exterior exposure conditions; any significant increase or decrease affects the protective properties and life 
expectancy of the coating proportionately.Alkyd finish s ystems of adequate thickness afford good protection 
in mild exposure conditions and offer a wide choice of colour. For exterior surfaces, gloss finishes should 
generally be used.  
 
NOTE 1 Aluminium paints (7/6), although giving rather thin films, have good protective properties and 
provide an economical finish for steel. They are also suitable for use on heated surfaces (see 8.3.4.4.2).  
 
NOTE 2 Micaceous iron oxide (MIO) paints (7/7) provide good protection and are widely used in 
situations where the limited  range of colours in which they are available is not a disadvantage. However, 
they can be overcoated with compatible gloss finishes (with the manufacturer's approval). MIO paints of 
normal type provide films of substantial thickness, and there are also hig h-build types, usually applied by 
airless spray, giving films of even greater thickness.  
 
Bituminous and tar paints (see Table 10), if applied in thick films, provide good protection against fresh and 
salt water and some chemicals in situations where colou r is not a requirement. When exposed to direct 
sunlight, they craze and chalk and should therefore be overcoated with bituminous aluminium paint. 
Generally, bituminous and tar paints should be applied over an inhibitive primer. The inhibitive primer should  
be allowed to harden (this can take several weeks) or a specially formulated primer should be used, as the 
solvents in some types of bituminous and tar paints can cause softening and lifting of the primer.  
NOTE 3 Table 14 indicates some typical coating systems for iron and steel in moderate exterior and 
interior exposure conditions.  
 
Specialist coatings, often in conjunction with metallic coatings, are usually necessary for severe conditions or 
where life expectancies in excess of those shown in Table 14  are required; in these circumstances, 
reference should be made to ISO 12944 -5 and BS 5493.  
 
8.3.4.4.2   Heated surfaces  
 
In addition to providing protection, paint systems applied to flues, chimneys, radiators, heating panels and 
other heated surfaces shou ld have the appropriate degree of heat -resistance in accordance with ISO 12944 -
5 or as follows.  
 
a) Up to about 50 °C. Normal paint systems as described in 8.3.4.4.1 (except bituminous and tar - 
based paints) are usually satisfactory (see Note).  
 
b) 50 °C t o 90 °C. Application of two coats of alkyd gloss finish or aluminium paint over primer as in a) 
is usually satisfactory; with coloured finishes, some discoloration of light colours can occur at the upper end 
of the range.  
 
c) 90 °C to 200 °C. Application of two coats of aluminium paint direct to clean bare metal is usually 
satisfactory although much depends upon the heating cycle. A coating that has withstood several months' 
exposure to temperatures at the higher end of the range can fail rapidly when the surface cools, especially if 
condensation occurs.  
 
d) Above 200 °C. Specialist coatings are likely to be required, and reference should be made to 
coatings manufacturers.   
68  © KEBS 2018 — All rights reserved   
Note:  Resistance to heat is influenced mainly by the maximum temperature reached in  service and the 
nature of the heating cycle, i.e. where sustained or intermittent and whether the surface is exposed to 
moisture. The behaviour of the coating is also influenced by the extent to which the surface remains dry 
when cold.  
 
8.4 Non-ferrous me tals and metallic coatings  
 
8.4.1  Characteristics  
 
8.4.1.1 General  
 
NOTE 1 Non-ferrous metals are more resistant to corrosion than iron and steel and, for this reason, are often used as alternatives. 
Some, notably zinc and aluminium, are used as protective  coatings for iron and steel.  
 
In most conditions, painting is not necessary except for appearance, but might be needed in some exposure 
conditions, e.g. in acid or severe marine or road salt conditions.  
 
A characteristic of some non -ferrous metal surfaces  is that special preparation or pre -treatment, or the use of 
primers of specific type, is always necessary to ensure satisfactory adhesion of paint. This is particularly so 
where thermally sprayed coatings are to be exposed externally where a sealer should  be applied prior to 
priming and over coating with the specified paint system.  
 
NOTE 2  Preparatory and pre -treatment methods are described in 8.4.2 and priming in 8.4.3  
 
8.4.1.2   Metallic coatings  
 
Zinc and aluminium are used extensively as protective coa tings, both individually and as alloys, for iron and 
steel structural members, sheets and components and consideration should be given to their use in 
moderate and severe exposure conditions and where long -term protection is required.  
 
Note  ISO 14713 gives  guidance on the selection and specification of metallic coatings.  
The different forms of coated product have a thickness or mass of coating, which depending on the product 
chosen should be selected to suit the expected severity of exposure or service requ irements.  
The application of zinc and aluminium coatings to iron and steel should be as follows:  
 
a) hot-dip galvanizing (zinc) for general steelwork and fittings (for further information see ISO  
14713) and claddings (for further information see BS EN 10326 and BS EN 10327);  
 
b) hot-dip aluminizing for the application of aluminium to steel;  
 
c) sherardizing (zinc) mainly for fittings, fasteners and small items (for further information see BS  
4921);  
 
d) electroplating (zinc) by electrolytic deposition of  zinc from zinc salt solutions for small items (for 
further  information see  BS  EN  12329,  BS  EN  12330  or  BS  3382),  as  well  as  for  sheet components;  
 
e) metal spraying (zinc, aluminium or their alloys, sprayed in a semi -molten form) for struct ural 
steelwork and plates after abrasive blasting (for further information see BS EN 22063) to be undertaken in 
the factory or, when conditions permit, on site.  
 
Metallic coatings may be painted under certain circumstances, such as for appearance or for ad ded 
protection in some exposure conditions.  
 
Special preparation or pre -treatment, or the use of primers of specific type, is essential in order to ensure 
satisfactory adhesion of paint (see 8.4.2 and 8.4.3). Appropriate sealer or paint systems usually adh ere 
satisfactorily to sprayed non -ferrous coatings  ISO 12944 if they are applied soon after the sprayed coatings.  
 
8.4.2  Surface preparation for non -ferrous metals  
 
8.4.2.1  General  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    69  
Preparation of new non -ferrous metal surfaces is concerned essentially w ith the removal of dirt, grease and 
corrosion products and treatment to improve paint adhesion, e.g. to galvanized surfaces and to aluminium 
sheets and extruded sections.  
 
Sprayed metallic coatings and aluminium castings will provide satisfactory adhesion for paint, but the 
surfaces should be clean and free from corrosion products and might require light abrasion. Etch priming 
may be necessary to improve adhesion.  
 
Non-ferrous metals are often left unpainted for many years, but painting might eventually be necessary for 
appearance or to arrest deterioration. If aluminium is left unpainted it can acquire a rough layer of corrosion 
products that should be removed before painting. Similarly, if erosion of metallic zinc coating from a 
galvanized substrate has ex posed the steel, any rust should be removed. However, if erosion of a thermally 
metal sprayed surface has exposed the steel, then the complete thermal sprayed coating should be removed 
prior to any painting.  
 
8.4.2.2  Degreasing  
 
Non-ferrous metals readily  retain grease and lubricants used in extrusion and drawing processes and these 
should be removed. On site, after cleaning off any gross contamination with an appropriate  cleaning fluid, 
e.g. a proprietary cleaning agent, surfaces should be washed using a detergent solution, rinsed and allowed 
to dry. Alternatively, surfaces should be wiped over with a proprietary cleaning agent and clean swabs; 
solvent and swabs should be changed frequently to avoid spreading the contaminant over the surface. In 
difficult cases more abrasive materials should be used.  
 
NOTE   Degreasing of thermally metal spra yed coatings and sheradizing can lead to problems with 
subsequent  paint coatings due to the porous nature of the coating, allowing absorption of the cleaning fluids 
which then remain trapped and can lead to premature breakdown of the paint coating.  
 
8.4.2.3  Removal of corrosion products  
 
Sprayed metallic coatings should be sealed (see 8.4.3.4) otherwise corrosion products can develop fairly 
rapidly, especially in damp or  chemically -charged atmospheres. Corrosion products could be detrimental to 
the metallic coating and affect paint adhesion. They should be removed before painting by scrubbing with 
clean water and stiff bristle or nylon (not wire) brushes, followed by rins ing with clean water.  
 
Removal of the rough layer of corrosion products which can form on aluminium after several years exposure 
can be difficult and abrasion might be necessary, e.g. with stainless steel wire wool or nylon pads, using 
water as a lubricant . Mild steel, brass, or copper wire should not be used, as broken strands can become 
embedded in the surface and stimulate corrosion.  
 
If non -ferrous metallic coatings on iron and steel are damaged or become eroded on long exposure, rusting 
of the exposed base metal is likely to occur. Rusted areas should be cleaned to bright metal and roughened 
by wire brushing or abrasion, care being taken to avoid damage to the adjacent sound zinc or aluminium 
coating.  
 
8.4.2.4   Pre-treatment (wash or etching) primers  
 
NOTE  Although included here with other preparatory treatments, pre -treatment primers have some of the properties of a 
conventional metal primer in addition to their essential function of assisting adhesion of paint systems to non -ferrous metals.  
 
Pre-treatment primers are applied as thin films.  The maximum film thickness specified by the manufacturer 
should not be exceeded. Except in very mild conditions, pre -treatment primers should be followed by a 
normal primer.  
 
The use of two -pack pretreatment prim ers (4/1) which are generally superior to one -pack types (4/2) is now 
being replaced by water -based adhesion primers (4/4) and mordant solutions (4/3, see 8.4.2.5) as ways of 
improving the adhesion of subsequent coating systems to zinc surfaces. Some pre - treatment primers are 
sensitive to moisture in the early stages and their suitability for use in conditions where they are likely to be 
exposed to rain or dew should be checked with the manufacturer.   
70  © KEBS 2018 — All rights reserved   
NOTE  The use of etch primers (either simple or two pack ) for hot -dip galvanized steel is rare.  
 
8.4.2.5   Chemical pre -treatments  
 
Zinc, aluminium and some other non -ferrous metals can be pre -treated to improve paint adhesion. Such pre -
treatment (e.g. phosphate) should be carried out under controlled, factory conditions. Site - applied 
treatments with proprietary washes can be less effective and can present difficulties in use, especially if final 
rinsing is required. A material for the pre -treatment of galvanized surfaces mordant solution (4/3), when 
properly a pplied, blackens zinc surfaces. If this does not occur, the surface should be thoroughly cleaned 
(see 8.4.2.3) and the treatment should be repeated. Excessive application of the wash (which, on horizontal 
surfaces can lead to ponding) and excessive thickne ss of coating should be avoided.  
 
8.4.2.6  Weathering  
 
Exposure of zinc and galvanized surfaces to weathering can improve paint adhesion, but the process is likely 
to take several months, even in conditions conducive to weathering, and the surface rarely w eathers 
uniformly, making it difficult to determine whether the surface has weathered sufficiently to be painted. Also, 
surfaces are likely to become soiled or contaminated especially in severe or very severe exposure 
conditions, e.g. industrial and marine , and should be washed (and degreased if necessary) before paint is 
applied. Weathering is unnecessary if the correct pre -treatments and/or primers are used (see 8.4.3).  
 
8.4.2.7  Abrasion  
 
Adhesion of paint to non -ferrous metals can be assisted by abradin g the surface with fine emery cloth, or 
abrasive paper and a proprietary degreasing agent; this method should be used for small areas prepared on 
site. Care should be taken not to abrade through thin films of pure aluminium on composite (clad) sheets; the 
use of steel wool or hard abrasives should be avoided on these surfaces. Light abrasion of galvanized 
surfaces by abrasive blasting (sweep blasting) can be effective at promoting the adhesion of subsequent 
coats of paint. It is important that a suitable, s oft blast medium is used, with low blast pressures (< 276 MPa) 
and an optimized and controlled blasting angle and nozzle -to-work piece distance maintained.  
 
8.4.2.8  Anodizing  
 
This is an electrolytic process used on aluminium in which a corrosion -resistant oxide film is deposited on the 
surface. Anodizing can provide a satisfactory surface for painting, but the process is expensive and is rarely 
used solely to facilitate painting. The advice of the paint manufacturer should be sought.  
 
8.4.3 Priming  
 
8.4.3.1  General  
 
Primers for non -ferrous metals should contain corrosion -inhibiting pigments (see F.4.5) but some such 
pigments which can be found in primers for iron and steel, e.g. graphite, are unsuitable as they can stimulate 
corrosion.  
 
Film thickness, although it has to be adequate, need not be so critical to the protection of non -ferrous metals 
as it is with iron and steel. In most conditions, one coat of primer in addition to the possible use of a pre -
treatment primer provides a satisf actory base for further coatings; in some circumstances, a pre -treatment 
primer alone might suffice. Special consideration should be given in certain micro - climates where soluble 
salts can collect on surfaces resulting in highly corrosive conditions where  corrosion products are not 
removed by normal ram washing and the formation of a passivating film of relatively insoluble oxides and 
other salts is not formed. Under such conditions, a greater film thickness, similar to that required for the 
protection of iron and steel should be used.  
 
Note: Recommendations in respect of primers for the non -ferrous metals in general use in buildings, 
assuming subsequent application of paints of conventional type, are described in 8.4.3.2, 8.4.3.3, 8.4.3.4, 
8.4.3.5, 8.4.3.6  and 8.4.3.7. Surfaces, preparatory treatments and primers are correlated in Table 15.  
 
8.4.3.2  Aluminium and its alloy  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    71 Although aluminium and its alloys vary in corrosion resistance, similar primers are used for all of them. Pre -
treatment primers should  be used for aluminium and its alloys to assist adhesion on smooth surfaces, e.g. 
sheets, extruded sections and aluminized steel.  
 
8.4.3.3  Zinc and zinc -coated (galvanized, sherardized and electroplated) steel  
 
Zinc reacts with most drying -oil/resin paint s, forming soluble salts (zinc soaps) beneath the paint film, which 
cause it to become embrittled and lose adhesion. The zinc should therefore be primed with a non -oil based 
primer. Pre -treatment primers (4/1, 4/2) can be used except possibly on galvanized  sheet.  
 
NOTE Unless otherwise specified (i.e. oiled or untreated), virtually all galvanized sheet produced  is passivated to prevent wet 
storage staining (white rusting) during storage. Such a treatment is likely to prevent pre -treatment primers reacting fully with the  zinc and 
it might also be incompatible with phosphate treatments. Galvanized sheet steel and components manufactured from such sheet, might 
need treatment with proprietary chemicals before pre -treatment or painting. Abrasion may be used to remove the orig inal passivation 
treatment but care needs to be taken to avoid excessive removal of the zinc coating, which would reduce the protective value of the 
system  
 
Water -borne acrylic (4/9) and two pack surface tolerant (4/10) can also be used to prime zinc. Pri mers 
formulated for direct application to zinc surfaces are satisfactory subject to the use of compatible topcoats.  
 
8.4.3.4  Sprayed metallic coatings  
 
Where sprayed zinc, aluminium and zinc aluminium alloy coatings are to be painted, following their 
appli cation they should be immediately coated with a pre -treatment primer, especially if they are to be 
exposed to damp or corrosive atmospheres; in order to retard the development of corrosion products which 
can affect the adhesion or appearance of the paint. If this is not done and corrosion products have 
developed, they should be removed (see 8.4.2.3) and the surface allowed to dry before application of the 
pre-treatment primer. Except in very mild conditions, the pre -treatment primer should be followed by on e coat 
of compatible primer.  
8.4.3.5   Copper and its alloys (e.g. brass and bronze)  
 
Copper and its alloys are rarely painted except for appearance. To aid the adhesion of paint these surfaces 
should be abraded with fine abrasive paper, wiped with a propri etary degreasing agent, and then a pre -
treatment primer should be applied. Indoors, direct application of alkyd gloss after abrasion is usually 
satisfactory. Special materials are available if a clear finish is required.  
 
8.4.3.6  Lead  
 
Abrasion as describ ed for copper (see 8.4.3.5), or treatment with phosphating solutions (see 8.4.2.5) should 
be undertaken to improve adhesion of paint to lead surfaces. Lead surfaces should not be abraded dry. Pre -
treatment primers and conventional metal primers, which do n ot contain graphite, should be applied to clean, 
grease -free surfaces.  
 
8.4.3.7   Chromium, nickel, tin and cadmium (as coatings)  
 
New chromium and nickel coatings rarely need painting, but it might be necessary if they become corroded. 
The surfaces should be lightly abraded to remove corrosion products before application of pre -treatment 
primer.  
 
Tin plate presents few difficulties in painting; most paints adhere after degreasing and light abrasion of the 
surface.  
 
Cadmium should not be weathered prior to painting. Phosphate treatment (see 8.4.2.5) or a pre - treatment 
primer (after light abrasion if necessary) can improve adhesion of subsequent coats. Cadmium plated 
surfaces should not be abraded dry.  
 
8.4.4  Coating systems for interior and exterior use  
 
In most situations, alkyd finish systems can be used, but when they are to be applied to pruned galvanized 
surfaces, it should be ensured that the primer and succeeding coats are compatible, otherwise adhesion 
failure can occur, especially in wet conditions.  Micaceous iron oxide paints can be used to provide added  
72  © KEBS 2018 — All rights reserved  protection to galvanized and metal -sprayed steel in moderate and many severe con ditions. Bituminous 
paints can be  used  for  contact  surfaces  and  where  colour  and appearance are not critical.  
 
Coatings for aluminium should not contain graphite pigments, which stimulate corrosion, as the priming coat 
might not isolate them from contact with the metal.  
 
Coating systems for non -ferrous metals are similar to those indicated for iron and steel in Ta ble 14, except 
that film thickness tends to be less critical and fewer coats can be used. In many moderate exterior and 
interior exposure conditions, three -coat systems (including primer) having a total thickness of about 85 µm 
might be adequate; in some i nterior situations, thinner films should be used. The life expectancy of 
comparable paint systems on non -ferrous metals tends to be greater than on iron and steel.  
 
For guidance on the selection of paint coatings for galvanized and metal -sprayed iron and s teel in severe 
exposure conditions, reference should be made to BS 5493.  
 
8.5  Plaste r, external rendering, concrete (including lightweight and autoclaved aerated 
blocks), brick and stone — General considerations  
 
Note: Plaster, external rendering, concrete, brick and stone have a number of characteristics in common 
and, to avoid repetition, these and general principles applying to the selection of paint for these substrate 
systems are considered here. For further information on the protection of con crete structures, see BS EN 
1504 -2 and BS EN 1504 -10. 
 
8.5.1  Characteristics  
 
8.5.1.1  Moisture content  
NOTE 1  Water, often in large quantities, is used with all the materials referred to and can also be absorbed as a result of storage of 
materials in the open without protection. Excessive moisture affects the adhesion of most types of paints, causes blistering and flaking 
and encourages the growth of moulds. Additionally, in combination with alkalis and salts contained in many wet materials of 
construction , it is the cause of other difficulties in relation to painting, including efflorescence, alkaline attack and staining.  
 
Until the contained moisture has substantially dried out, there is some degree of risk in applying most types 
of coatings. Drying out c an take a long time even in favourable conditions, a rough estimate being one week 
of good drying conditions for each 5 mm thickness of wet construction (typically 4 weeks to 6 weeks).  
 
Electrical moisture meters should be used to determine the moisture co ntent of the substrate. They are easy 
and convenient to use and enable a number of readings to be taken quickly. If a wall is believed to be damp 
but meter readings at a shallow depth indicate low moisture content, the area should be covered with a sheet 
of polyethylene and rechecked 24 h later. If there is adjacent woodwork, its moisture content should be 
determined, as there is less likelihood of soluble salts being present in wood and so readings are more 
reliable, especially if they are significantly lo wer for the wood.  
 
NOTE 2 The first column in Table 16 and Table 17 refers to four stages of drying of walls, i.e. dry, drying, damp, and wet, and give s 
corresponding equilibrium humidity percentages.  
 
8.5.1.2  Efflorescence  
 
Efflorescence, usually sodium sulfate, is likely to disrupt relatively impermeable (e.g. solvent -borne) paints 
but can come through more permeable (e.g. water -borne) paints without much disruption although their 
adhesion might be impaired. It is undesirable, therefore, to apply even pe rmeable paints until efflorescence 
has ceased. As it occurs, it should be removed with a dry cloth or brush, and collected in bags. This should 
be followed by wiping with a damp cloth wrung out frequently in clean water avoiding excessive wetting. This 
treatment should be repeated at intervals of a few days until efflorescence has ceased. A proprietary acid 
wash may also be used.  
 
8.5.1.3  Calcium carbonate deposits  
 
Thin, hard film known as lime bloom cannot be wiped off but can usually be softened and rem oved with a 
steam gun and scraper. Lime bloom can be over -painted without much risk of disruption provided the 
substrate is substantially dry. The glazed surface might impair adhesion and should be lightly abraded to 
prevent this.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    73 8.5.1.4  Alkalinity  
 
NOT E Materials containing Portland cement (CEM 1) or lime are strongly alkaline; gypsum plasters are not 
usually alkaline in themselves but might become so if they are gauged with lime or it is brought forward from 
backings during drying. Alkalinity diminishes with ageing, but the process can take several years with 
cement -based products.  
 
Drying -oil/resin paints are likely to be saponified (softened or liquefied) by alkalis in the presence of moisture. 
Water -borne paints are not attacked in this way but can be weakened or bleached by strong alkalis. Some 
special purpose paints, notably those based on chlorinated rubber or epoxy resins, are not attacked but may 
only be applied to dry substrates, and this usually precludes their use on new work. Cement -based paints 
are also resistant to alkaline attack. Some pigments are attacked by alkalis, causing fading or discoloration, 
but paints intended for use on substrates that might contain alkalis are usually formulated with resistant 
pigments.  
 
Alkali -resisti ng primers (5/1) provide a measure of protection against alkaline attack and should be used 
beneath solvent -borne systems applied to substrates in which alkalis might be present. However, it cannot 
be too strongly emphasized that the essential function of primers is to dimmish the risk of failure on 
substrates that are substantially dry, and they do not obviate the need to allow time for this condition to be 
reached.  
 
Alkali -resisting primers can also improve the performance of water -borne paint on cement -based substrates; 
if so used, they should be applied thinly to avoid producing a glossy surface to which water -borne paint might 
not adhere satisfactorily.  
 
 
8.5.1.5  Staining  
 
NOTE  Brown stains with no appreciable surface deposit sometimes appear on water -borne paints but do 
not normally affect solvent -borne paints. They are usually derived from substrates, notably certain types of 
brick, hollow clay pot or clinker block, containing soluble salts or colouring materials, or from sands 
containing biological m atter that reacts with alkali.  
 
If it is suspected that brown staining is likely to occur, a coat of primer should be applied to prevent it and 
should also be used over stained water -borne paint to prevent staining of succeeding coats. The substrates 
shoul d be substantially dry and, for the reason indicated in 8.5.1.4, the primer should be applied thinly.  
 
8.5.2  Coating systems for interior use  
 
8.5.2.1  General  
 
The choice of paint systems for substrates employing wet  materials of  construction should be  determined 
by the moisture content at the time of painting. Where time is allowed for drying out, the conditions of service 
and the requirements in respect of appearance, i.e. colour, sheen level and texture, should be taken into 
account in the choice of p aint systems.  
 
Mid-sheen or matt finishes should be used for walls and ceilings as they minimize the effect of surface 
irregularities and reduce reflection of light sources. Their resistance to wear and repeated washing is 
generally relative to the degree of sheen, and mid -sheen or matt finishes are less suitable than gloss finishes 
for use in hard -wear conditions.  
 
8.5.2.2  Mid-sheen and matt water -borne paints  
 
Mid-sheen and matt water -borne paints are permeable, reasonably resistant to alkaline attack an d therefore 
suitable for use on substrates that are not completely dry, but they should not on this account be misused, 
e.g. applied to damp surfaces within a few days of plastering. Permeability is generally proportionate to the 
level of sheen; the matt c ontract types (7/5) are the most permeable although they are less resistant to wear 
and frequent washing than the other types. Water -borne paints applied to reasonably dry substrates usually 
provide a satisfactory base for most of the types of paint that m ight be required for maintenance painting.   
74  © KEBS 2018 — All rights reserved   
8.5.2.3  Solvent -borne alkyd finishes  
 
Solvent -borne alkyd finishes are less permeable and more susceptible to alkaline attack than their water -
borne paint counterparts and should be applied to completely dry subs trates over a primer.  These have good 
resistance to wear and frequent washing but should be applied only to dry primed substrates. If the 
conditions of service warrant the use of a solvent -borne gloss finish and there is insufficient time for drying 
out, w ater-borne paint should be used as a temporary measure and the gloss finish system applied when 
drying out is complete. Use of solvent -borne finishes on large areas should be avoided as this can give rise 
to solvent vapour hazards. Breathing apparatus shou ld be worn when using solvent -borne products.  
Note:  For further information on health and safety when working with solvent -borne products, see Annex B.  
 
8.5.2.4  Water -borne acrylic gloss finishes  
 
Water -borne wall paints have similar resistance to wear an d frequent washing as their solvent -borne alkyd 
counterparts and minimize the health risks to the operator by reducing their exposure to solvent vapours. 
They have greater tolerance of substrate moisture and allow surfaces that are substantially dry (i.e. drying) 
to continue drying out.  
 
8.5.2.5  Textured coatings  
 
Textured coatings can be used for their decorative effect, to hide surface defects or irregularities and as an 
alternative to plastering or rendering. Coatings of this type include plastic -texture d paints (7/15) and water -
borne, heavy -textured masonry paints (7/9). They are usually relatively permeable and moderately resistant 
to alkaline attack and can be suitable for direct application to surfaces not completely dry, but reference 
should be made to manufacturer's recommendations.  
 
8.5.2.6  Multi -colour finishes  
 
Multi -colour finishes are very hardwearing and especially suitable for use on walls in circulating areas, 
cloakrooms and similar locations. Generally, they should be applied only to substantially dry substrates, 
usually over special primers or base -coats, but manufacturer's recommendations regarding surface 
conditions and systems should be followed.  
 
8.5.2.7  Cement paints  
 
Cement paints are permeable, resistant to alkaline attack and  suitable for early application to most 
substrates except gypsum plaster, although their rough surface and limited colour range can preclude their 
use if ease of cleaning and decorative appearance is important. They can also impose limitations on the 
choic e of maintenance paints. Cement paints should be applied directly without priming.  
 
8.5.2.8  Silicate -based masonry coatings  
 
The recommendations in 8.5.3.6 should be followed for silicate -based masonry coatings for coating systems 
for interior use.  
 
8.5.3  Coating systems for exterior use  
 
8.5.3.1  General  
 
Coating systems for exterior use are painted principally to enhance their appearance by imparting colour and 
texture or, in some cases, to prevent rain penetration. A range of specialized coatings (11/1 to 11/4) can also 
be used, to protect the surface of concrete, etc. from potentially harmful agents, e.g. carbon dioxide, sulfur 
dioxide and salts and the manufacturer's recommendation should be followed. Initial painting and  
subsequent maintenance can  b e costly and,  in  designing new buildings, consideration should always be 
given to the use of alternative means of achieving the desired objectives, e.g. by using self -coloured 
renderings or facings which require infrequent maintenance or are resistant to  ram penetration.  
 
Painting might be necessary to provide a uniform appearance when repairs or alterations have been carried 
out. Although external walls are often not painted until many years after erection, they should still be 
regarded as new; the consi derations in respect of moisture content described in 8.10.1.1 should be applied, KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    75 especially when rain has penetrated or repairs have been carried out. Additionally, mould and other 
biological growths might be present, and preparatory treatment to deal wit h these should be carried out as 
described in 11.5.8.  
 
It is essential that masonry paint not be used as a cure -all coating for rising damp, walls affected by water 
ingress from failed rainwater gutters and downpipes and failed lead flashing. It will fail very quickly in these 
circumstances. Preventive maintenance should be carried out first to overcome water ingress into the 
substrate before the application of coatings.  
 
Scaffolding should be positioned well off the work face to avoid patterning which is a pparent once the 
scaffold rig is removed.  
 
8.5.3.2  Gloss finishes  
 
Gloss finishes are seldom used on external walls except in repainting work on smooth renderings or stucco. 
If solvent -borne gloss finishes are used, the substrate should be dry and an alka li-resistant primer should be 
applied.  
 
Water -borne gloss finishes should be used in suitable conditions of temperature and humidity for satisfactory 
film formation and drying.  
 
8.5.3.3  Mid-sheen and matt finishes  
Alkyd mid -sheen and matt finishes, as use d for internal surfaces, are not suitable for external walls, where 
water -borne masonry paints (7/8) or, on substantially dry substrates, solvent -thinned masonry paints (7/10) 
should be used.  
 
8.5.3.4 Textured finishes  
 
Note: Textured finishes are wide ranging from a fine sand or stone texture to heavy -texture coatings 
containing coarse aggregate or deriving their texture from the method of application. Examples of the types 
available are given in 7/8 to 7/11.  
 
Textured coatings should be used where grea ter durability is needed. The thicker or more heavily textured 
coatings also help to hide surface irregularities, fill fine surface cracks and contribute to the rain resistance of 
external walls. They should not be used to improve the acoustic or thermal i nsulation properties of walls as 
they are too thin. They can be used to prevent reduction of the original thermal insulation value by reducing 
rain penetration.  
 
Dirt pick -up could be a problem with the heavier textures in polluted atmospheres although the rough texture 
tends to promote an evenness of soiling that might be less apparent than on a smooth surface.  Some thick, 
textured sprayed coatings are applied by specialist applicators and might be offered with a warranty as to 
their durability; because  of the wide range of types and compositions available, manufacturer's 
recommendations should be ascertained.  
 
8.5.3.5 Cement paints  
 
On external exposure, algal growth is prone to develop on cement paints applied to surfaces that are 
persistently damp alt hough some paints incorporate a fungicide. Cement paints should not be used in acidic 
exposure conditions.  
 
8.5.3.6 Silicate -based masonry coatings  
 
Note: Silicate -based masonry coatings (mineral paints) have been used in continental Europe for a 
considera ble time in grades suitable for external and internal surfaces. These coatings provide inert non -
flammable films that do not support fungal and algal growth and are compatible with all mineral building 
materials. Compositions of high water vapour permeabil ity are available.  
  
76  © KEBS 2018 — All rights reserved  External surfaces to be painted should be free from dirt and all previous paint coatings. Application should be 
by brush, roller or spray. The drying coating can be susceptible to rain damage.  The liquid paints are highly 
alkaline and h ence precautions should be taken during application.  
 
8.6 Plaster  
 
8.6.1  Characteristics  
 
8.6.1.1  General  
 
The plasters in general use for internal work should comprise one or more of the following:  
 
a) calcium sulfate (gypsum) types, other than lightweig ht plasters, conforming to BS 1191 -1 (see 
8.6.1.2);  
 
b)  calcium sulfate (gypsum) lightweight plasters conforming to BS 1191 -2 (see 8.6.1.2);  
 
c)  thin-wall plasters (see 8.6.1.3); d)    cement plasters (see 8.6.1.4); e)    lime plasters (see 8.6.1.5).  
 
NOTE For further information on plaster, see Annex I. For further information on plasterboard, see Annex J.  
 
8.6.1.2   Calcium sulfate (gypsum) plasters  
Used neat and when fully dry and set, calcium sulfate (gypsum) plasters can be painted without difficulty  with 
most types of paint. Added lime (or cement in backing coats), in the presence of moisture, might cause 
alkalinity, and therefore an alkali -resistant coating should be used.  
 
8.6.1.3  Thin -wall plasters  
 
Thin-wall plasters are based on organic binders  and to dry out rapidly are used in thin layers. They normally  
present  no  difficulties  in  painting  when  used  on  dry  backings  but  sometimes appear underbound and 
can be excessively absorbent; in these cases, treatment as described in 8.6.2.4 sho uld be carried out.  
 
8.6.1.4  Cement plasters  
 
Cement: sand or cement: sand: lime plasters should be used where strong, hard or moisture -resistant 
surfaces are needed. They should not be painted until they have substantially dried out, as they are strongly  
alkaline and likely to attack drying -oil/resin paints.  
 
8.6.1.5  Lime plasters  
 
Note: Non -hydraulic lime plasters made with high -purity lime and clean sand are free from soluble salts and 
caustic alkali but can react with salts from backing to form causti c alkalis which attack drying -oil/resin paints 
and some water -borne paints if they are applied before the plaster has substantially dried out. Hydraulic lime 
plasters are variable in caustic alkali content and can attack paints severely.  
Lime plasters shou ld not be painted until they have substantially dried out, as they are strongly alkaline and 
likely to attack drying -oil/resin paints.  
 
8.6.2  Surface preparation and priming of plaster  
 
8.6.2.1  Cleaning  
 
Dirt and loose surface deposits should be removed b y dry brushing. Plaster nibs and splashes should be 
scraped off, care being taken to avoid damaging the surface. Efflorescence, if present, should be treated as 
described in 8.5.1.2.Mould growth can occur on plastered surfaces if drying out  has been prolon ged, 
especially in conditions of poor ventilation. The affected areas should be treated as described in 11.5.8.3.  
 
8.6.2.2  Treatment of stains  
 
For the treatment of stains, the recommendation in 8.5.1.5 should be applied  
 
8.6.2.3  Stopping and filling  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    77  
Cracks, holes and surface imperfections should be stopped and filled with plaster, water -mixed filler or, in 
cement plasters, with masonry cement, before application of first or priming coats.  
 
8.6.2.4  Priming  
 
NOTE  Recommendations for priming are given i n Table 16.  
 
Priming is essential when solvent -borne paint systems are applied to plaster; it is not usually necessary with 
water -borne paints, but see 8.5.1, in particular 8.5.1.4 and 8.5.1.5.  
 
When water -borne paints are applied to plaster of high or var iable porosity, differential absorption can cause 
difficulties in application or variations in colour or sheen, which can persist through several coats. A well -
thinned first coat of water -borne paint, sometimes referred to as a sealing or mist coat, often overcomes the 
problem but is likely to have relatively poor opacity and, if it is required, should be regarded or specified as 
an additional coat in the system. Where this proves inadequate a coat of alkali -resisting primer (5/1) or 
primer -sealer (5/3) sho uld be applied, but this should be done only if the substrate is substantially dry. The 
primer or primer -sealer might need thinning to ensure that it does not provide a glossy surface to which 
water -borne paint might not adhere satisfactorily.  
 
8.6.3  Coati ng systems for plaster  
 
The selection of coating systems for plaster should be in accordance with 8.5.2 and 8.5.3, and details of 
systems are incorporated in Table 16.  
 
8.7 External renuenug  
 
8.7.1  Characteristics  
 
8.7.1.1  Cement renderings  
 
The rendering s in general use are cement -based and might incorporate hydrated lime. They might not 
require painting when new, although this might eventually be necessary for appearance or if repairs are 
carried out. However, they should not be painted until they have s ubstantially dried out, as they are strongly 
alkaline and likely to attack drying -oil/resin paints.  
 
8.7.1.2  Stucco  
 
Note:  Stucco can be made from lime/sand (pre 1790), Roman or Portland cement -based (dating from about 
1790) or oil mastic (1790 to 1820).  
 
Where deterioration or removal of the paint coating exposes the original surface, repainting might be 
undertaken. In order for repainting to be undertaken, the rendering should be sound and dry.  
 
8.7.1.3  Repairs to renderings  
 
If repairs to old renderings, including stucco, are necessary, they should be carried out in accordance with 
BS 5262, using cement -based mixes. The repaired portions should then be treated as for new work in 
respect of painting.  
 
8.7.2  Coating systems for external rendering s 
 
8.7.2.1  Surface preparation  
 
8.7.2.1.1  Cleaning  
 
New surfaces normally should be brushed down with stiff (not wire) brushes to remove loose material. 
Efflorescence should be treated as described in 8.5.1.2. Old unpainted surfaces, especially if rough or 
textured, might require more rigorous treatment, including washing down, to remove accumulated dirt before  
78  © KEBS 2018 — All rights reserved  painting. If washing is necessary, time should be allowed for drying out. Biological growths might be present 
on old surfaces and should be treate d as described in 11.5.8.  
 
8.7.2.1.2   Treatment of stains  
 
The recommendations given in 8.5.1.5 should be applied for the treatment of stains.  
 
8.7.2.1.3   Stopping and filling  
 
Minor cracks, holes and surface defects should be made good with exterior grade  water -mixed cement -
based filler or masonry cement before application of the primer or first coat of paint.  
 
8.7.2.2   Priming  
 
NOTE  Recommendations for priming are given in Table 17.  
 
When solvent -borne paint systems are to be applied, external renderings should be primed; it is not usually 
necessary with water -borne paints but see 8.5.1.4 and 8.5.1.5. This should be confirmed with the paint 
manufacturer.  
 
To accommodate variations in surface porosity and assist application, primers or first coats can be th inned in 
accordance with the manufacturer's instructions.  
 
8.7.2.3  Finishing  
 
The selection of coating systems for external renderings should be in accordance with 8.5.3, and details of 
systems are incorporated in Table 17.  
 
8.8 Concrete  
 
8.8.1  General  
 
Concrete does not usually require painting for protection although this might be necessary to prevent long -
term deterioration in aggressive atmospheres. Protective painting, using chemical -resistant paints, might also 
be necessary to prevent further penetr ation of carbon dioxide, water and salts after repair of deteriorated 
concrete, or even on new concrete if the thickness and integrity of concrete over reinforcement is insufficien t 
to provide protection. In most circumstances, however, concrete is painted  to improve its appearance, 
especially on large areas.  
 
In  relation  to  painting,  the  general  characteristics of  concrete  are  similar  to  those  of  external 
rendering. Because of the greater thicknesses usually involved, it can take concrete much  longer to become 
dry enough to paint without restrictions on the choice of paints. The surface finish of concrete can vary 
widely from smooth and dense (e.g. with pre -cast components) to rough and porous with large voids. 
Specialist advice should be sough t in cases where it is difficult to achieve a good, uniform coating unless a 
suitable filler or sealer has been used.  
 
Residues of release agents present on the surface of cast and shuttered concrete can seriously impair the 
adhesion of paints and should b e removed. Laitance on trowelled and floated surfaces can also impair 
adhesion and should be removed.  
 
8.8.2  Coating systems for concrete  
 
8.8.2.1   Surface preparation/cleaning  
 
On new surfaces, deposits and loose material, including laitance, should be removed by scraping and 
brushing with stiff (not wire) brushes. On large areas, it might prove more effective to abrasive blast surfaces 
(using non -ferrous abrasives) to remove laitance and glaze on shuttered surface and expose.fine aggregate. 
On smooth, s huttered surfaces, paint adhesion might be enhanced when roughened by abrasive blasting. If 
efflorescence is evident, it should be treated as described in 8.5.1.2.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    79 Residues of release agents should be removed with detergents or emulsifying agents rather t han with 
solvents, which can simply spread the contaminant.  
 
Old unpainted surfaces might require washing to remove accumulated dirt before painting; if this is 
necessary, time should be allowed for drying out before painting. Surfaces on which biological growths are 
present should be treated as described in 11.5.8.  
 
8.8.2.2 Stopping and filling  
 
Large voids and air -holes should be filled with masonry cement or epoxy resin mortars. Minor surface 
defects should be made good with interior or exterior grade wa ter-mixed cement -based filler or with masonry 
cement. Application of cement paint or bagging with a cement:sand slurry can reduce surface roughness and 
fill minor imperfections.  
 
8.8.2.3 Priming  
 
NOTE  Recommendations for priming are given in Table 16 and Table 17.  
 
When solvent -borne systems are used on concrete a primer should be applied; it is not usually necessary 
with water -borne paints but see 8.5.1.4 and 8.5.1.5. This should be confirmed with the paint manufacturer.  
 
To accommodate variations in surf ace porosity and assist application, primers or first coats can be thinned in 
accordance with the manufacturer's instructions.  
 
8.8.2.4 Finishing  
 
The selection of coating systems for concrete should be in accordance with 8.5.2 and 8.5.3, and details of 
systems are incorporated in Table 16 and Table 17.  
 
Coatings which are applied to give additional protection should be of an impervious type, e.g. bituminous or 
other specialized coatings (7/8, 7/10, Table 10 and Table 11), to prevent ingress of water, corro sive salts and 
gases; and should be applied only to dry surfaces.  
 
Note: By protecting the integrity of the concrete cover over mild or high -tensile steel reinforcement, the time 
to initiation of disruptive corrosion is extended, as well as reducing the ra te of further deterioration of repaired 
existing concrete.  
 
Periodic maintenance is needed. Further guidance on the selection of specialist coatings for the protection of 
concrete both new and repaired is given in BS EN 1062 -1 and BS EN 1504 -2. 
 
8.9 Brick  and stone  
 
8.9.1  Characteristics  
 
Brick and stone are durable materials, generally of attractive natural appearance and, when new, do not 
usually require painting.  
 
NOTE 1  For information on the characteristics of brick an stone, see Annex K.  
 
On older buildings, painting might be necessary to improve appearance, hide repairs and alterations or 
reduce rain penetration. On large buildings, painting of external masonry essentially for cosmetic reasons 
should be undertaken only after consideration of the im plications in respect of maintenance expenditure.  
 
Generally, brick (other than concrete bricks) and stone are not, in themselves, alkaline, but the mortars used 
in construction are usually strongly alkaline and, until dry, are likely to give rise to the d ifficulties in painting 
described in 8.5.1.4. Efflorescence can also occur on brickwork and stonework and should be treated in 
accordance with 8.5.1.2.  
  
80  © KEBS 2018 — All rights reserved  NOTE 2 Where external brickwork and stonework are exposed to severe weathering conditions, e.g. 
in para pet, freestanding and retaining walls and below ground level damp -proof courses, it is difficult to 
ensure that moisture does not penetrate.  
 
If moisture penetration occurs, paint coatings are likely to be disrupted; also, they can prevent or retard 
drying  out of moisture and thereby increase the risk of the brick or stone being damaged by frost. It is 
recommended that, in these situations, brickwork and stonework should not be painted.  Concrete blocks are 
strongly alkaline and an alkali -resisting system sh ould be used preferably when the brickwork has 
substantially dried out.  
 
The adhesion of conventional paints to the harder, non -porous stones, especially if the surface is smooth or 
polished, is likely to be poor and, if painting is essential, paints of th e types recommended for glazed bricks 
(see 8.14.2) should be used. Where bricks contain high levels of ferrous oxide, a stain block primer should 
be used for sealing.  
 
Note: Some bricks can contain high levels of ferrous oxide which can be present in the r aw materials, in 
certain parts of the country. This can cause iron staining which will bleed through most water -borne coatings.  
 
8.9.2  Coating systems for brick and stone  
 
8.9.2.1   Surface preparation/cleaning  
 
New surfaces, e.g. fair -faced brickwork, should be brushed down with stiff (not wire) brushes to remove 
loose material. Efflorescence should be treated as described in 8.5.1.2. Heavily soiled and old unpainted 
surfaces might require more vigorous treatment, including high pressure washing down, t o remove 
accumulated dirt. Cleaning should be carried out in accordance with BS 8221 -1. When washing has been 
carried out, time should be allowed for drying out before painting. Biological growths might be present on old 
external surfaces and should be tre ated as described in 11.5.8.  
 
8.9.2.2   Stopping and filling  
 
On old, unpainted surfaces, repairs and re -pointing should be carried out well in advance of painting to 
facilitate drying out.  
 
Minor surface defects should be made good with ulterior or exterior grade water -mixed filler or with masonry 
cement.  
 
8.9.2.3   Priming  
 
Note: Recommendations for priming are given in Table 16 and Table 17.  
 
Priming is necessary with solvent -borne systems and, because mortar joints are likely to be alkaline, an 
alkali-resisting primer should be used.  
 
Priming is not usually necessary with water -borne paints, but see 8.5.1.4, 8.5.1.5 and 8.9.1. This should be 
confirmed with the paint manufacturer.  
 
To accommodate variations in surface porosity and facilitate applicat ion, primers or first coats should be 
thinned strictly in accordance with the manufacturer's instructions.  
 
8.9.2.4  Finishing  
 
The selection of coating systems for brick and stone should be in accordance with 8.5.2 and 8.5.3, and 
details of coating system s are incorporated in Table 16 and Table 17.  
 
Note: Further guidance on surface protection systems for concrete is given in BS EN 1504 -2. 
 
8.10 Precast concrete blocks  
 
Note: For further information on concrete blocks, see Annex K.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    81 8.10.1  Characteristics  
 
8.10.1.1   Moisture content  
 
To minimize drying shrinkage, blocks should be kept as dry as possible, particularly during site storage. The 
moisture content of new blockwork is unlikely to cause serious difficulties in painting but time should be 
allowed fo r drying out of the mortar joints before painting.  
 
8.10.1.2   Alkalinity  
 
New concrete blocks are strongly alkaline and an alkali -resisting system should be used preferably when the 
blockwork has substantially dried out.  
 
8.10.1.3  Porosity  
 
Concrete  blocks  vary  considerably in  porosity  and  absorption  according to  their  manufacturing process, 
density and the nature of the aggregate used, but even the densest blocks are usually sufficiently porous to 
afford satisfactory adhesion for paint. The m ore open and porous materials, however, need a more 
protective system in exposed situations. Primers or first coats should be thinned in accordance with the 
manufacturer's instructions.  
 
8.10.1.4   Texture  
 
Blockwork is often painted directly to save the cost of rendering or plastering, but it should be appreciated 
that  normal  paint  systems  do  not  completely mask  the  texture  of  the  blocks  and attempting to smooth 
the surface by conventional filling methods is rarely satisfactory. Roller or spra y application of heavy -bodied, 
thick coatings (7/9 or 7/11) can usefully combine both protective and aesthetic functions. When appearance 
is important, blocks having an acceptable surface texture, e.g. of facing quality, should be used, paint being 
used to  complement the texture rather than mask it.  
 
8.10.2  Coating systems for precast concrete blocks  
 
8.10.2.1   Surface preparation/cleaning  
 
The surfaces of precast concrete blocks should be brushed down with stiff (not wire) brushes to remove 
loose material.  Efflorescence, if present, should be treated as described in 8.5.1.2.  
 
8.10.2.2   Stopping and filling  
 
If necessary cracks, holes and damaged areas should be made good with cement mortar, masonry cement, 
or, in dry interior conditions, with water -mixed fi llers.  
 
As indicated in 8.10.1.4, overall filling of the surface of blockwork by conventional methods is not 
recommended. On the finer -surfaced blocks, a cement/sand slurry or cement paint scrubbed into the surface 
reduces texture and fills small holes. Th ick textured coatings are also useful in this respect (7/9 and 7/11).  
 
8.10.2.3   Priming  
 
NOTE  Recommendations for priming are given in Table 16 and Table 17.  
 
Priming is necessary with solvent -borne paint systems, and an alkali -resisting primer should be used. 
Priming is not usually required when water -borne paints are used, but see 8.5.1.4 and 8.5.1.5. This should 
be confirmed with the paint manufacturer.  
 
To accommodate variations in surface porosity and assist application, primers or first coats can be thinned in 
accordance with the manufacturer's instructions.  
 
8.10.2.4   Finishing  
  
82  © KEBS 2018 — All rights reserved  The selection of coating systems for concrete blockwork should be in accordance with 8.5.2 and 8.5.3, and 
details of coating systems are incorporated in Table 16 and Table 17 . 
 
NOTE  Further guidance on surface protection systems for concrete is given in BS EN 1504 -3. 
 
8.11 Cement -based sheets, boards and components  
 
WARNING  Materials containing asbestos are subject to the legislation that requires precautions to be 
taken in handling them to ensure that they do not constitute a hazard to health (see Annex B). Cement -
based insulating materials containing asbestos fibre, if found, should not be disturbed. Unknown cement -
based insulating materials should be treated as containing asbestos fibre until properly identified. Specialist 
advice should be sought on the treatment of all asbestos containing materials and if necessary the correct 
method for its safe removal and disposal.  
 
8.11.1  Coating systems for cement -based sheets, board s and components  
 
8.11.1.1   Surface preparation/cleaning  
 
New surfaces should be brushed down with stiff (not wire) brushes to remove loose material. With materials 
containing asbestos, precautions to prevent inhalation of dust are essential (see WARNING t o 8.11 and 
Annex B).  
 
Biological growths might be present on old, unpainted external cladding and roofing materials; if so, the 
surfaces should be treated as described in 11.5.8.  
 
8.11.1.2 Stopping and filling  
 
The necessity for filling does not normally a rise with external cladding and roofing materials or with internal 
linings when patent fixing methods are used. When internal linings are fixed by nailing or screwing, a water -
mixed filler (see 7.4.4) should be used for stopping.  
 
Where a high standard of finish is required on flat internal surfaces, smooth -surface boards should be 
specified but, if necessary, water -mixed fillers can be used.  
 
8.11.1.3   Priming  
 
NOTE  Recommendations for priming are given in Table 16 and Table 17.  
 
Alkali -resisting primers might not be strictly necessary in solvent -borne paint systems for some types of 
cement -based insulating boards of low alkalinity, but there is no disadvantage in their use.  
 
Alkali -resisting primers of conventional type, as normally used in solvent -borne paint systems, should not be 
used under chlorinated or acrylated rubber paints (see 8.11.1.5). The latter should be applied directly to the 
surface or over a chlorinated or acrylated rubber -based primer, as recommended by the paint manufacturer.  
 
Asbestos -cement goods vary in porosity, and cement -based insulating boards can be highly porous. Primers 
or first coats should be thinned strictly in accordance with the manufacturer's instructions to accommodate 
variations in surface porosity and facilitate applic ation.  
 
8.11.1.4   Back -painting  
 
Under certain circumstances, as indicated in K.3.2, fibre -cement sheets should be back -painted to prevent 
differential carbonation. For this purpose, impermeable paints of similar type to those used on the exposed 
surface s hould be used; alternatively, a cheaper material, e.g. bituminous paint, can be applied  
 
8.11.1.5   Finishing  
 
The types of coating system described in 8.5.2 and 8.5.3 and the systems shown in Table 16 and Table 17 
are suitable for use on cement -based sheet s, boards and components. If, however, a gloss or semi -gloss 
finish is required for asbestos -cement roofing and cladding sheets and components, chlorinated or acrylated KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    83 rubber paint (which does not require an alkali -resisting primer) should be applied in p reference to the system 
of alkali -resisting primer, undercoat and finish used with gloss finishes of conventional type.  
 
8.12 Paper and wallcoverings including plasterboard  
 
8.12.1  Characteristics  
 
8.12.1.1  General  
 
Problems can be experienced in respect of painting existing coloured wallcoverings.  
 
NOTE   For information on general characteristics of paper wallcoverings and plasterboard, see Annex J.  
 
8.12.1.2  Wallpapers  
 
The metallic inks used in some patterns can react with water -borne paints and cause discoloration. In the 
past, wallpapers containing "gold" or red colours in their pattern, often gave rise to discoloration. Therefore, a 
test area should be painted on such papers to see if discoloration occurs; if it does, a solvent -borne primer or 
knotti ng should be applied to seal the surface of the paper (see 8.12.1.3) or the paper should be removed.  
 
It should be appreciated that application of paint to wallpaper makes its removal more difficult, should this be 
necessary at a later date, especially if solvent -borne paints are used. Wallpaper should be painted only if it is 
firmly adhering and without blisters, creases or prominent joins.  
 
8.12.1.3  Vinyl wallcoverings  
 
These can be vinyl -faced (e.g. paper -backed) or sheet vinyls. Vinyl wallcoverings can  be painted, but 
migration of plasticizer from the vinyl into the paint coating could cause softening or the development of 
glossy patches in mid -sheen finishes. It is not possible to assess the likelihood of this by short -term tests 
and, in cases of doubt , the manufacturer of the wallcovering and/or paint should be consulted.  
 
Vinyl wallcoverings should be removed by lifting a corner and peeling away the vinyl coated surface layer. 
The remaining sheet can be used as a sub surface for painting provided the surface adhesion is sound.  
 
8.12.1.4   Non-woven papers or vinyl coated non -wovens  
 
Non-wovens are wallcoverings containing a proportion of synthetic content. Non -woven papers or vinyl 
coated non -wovens allow for virtually direct removal in a single dry str ippable sheet. Any issues such as 
metallic inks or plasticizer migration arising (as described in 8.12.1.2 or 8.12.1.3) should be resolved by 
removing the wallcovering.  
 
8.12.2  Removal of paper and wallcoverings  
 
In order to assess how much time is needed for the removal of the paper and wallcoverings, the following 
information should be included in the specification:  
 
a)  type of paper/wallcovering being removed;  
 
b) whether the paper and wallcoverings have been painted;  
 
c) the number of layers to be removed.  
CD/K/034:2009  
 
8.12.3  Coating systems for paper, wallcoverings and plasterboard  
 
8.12.3.1   Surface preparation  
 
Newly -hung lining paper and wallcoverings should be allowed to dry out completely before painting. Dry 
surfaces should be lightly brushed to remove loose material.  
  
84  © KEBS 2018 — All rights reserved  With existing wallcoverings, loose material should be refixed with the recommended adhesive; if adhesion is 
generally suspect, painting makes it worse and the wallcovering should be removed.  
 
Wallco verings affected by mould growths should be removed and the source of the mould investigated. 
Subsequently, the surface should be treated as in 11.5.8.3.  
 
If water -borne paints are to be used and there is a risk of discoloration (see 8.12.1.2), a test area  should be 
coated with the  paint it  is  proposed to  use  and should be inspected after  24  h.  If discoloration occurs, it 
can be prevented by applying a coat of knotting (see 7.4.3) or solvent -borne primer (5/1 or 5/3) overall or to 
the areas responsi ble. Alternatively, the wallcovering should be removed.  
 
8.12.3.2  Joint treatment  
 
Other than in plasterboard dry -lining systems, it is not possible to hide joints satisfactorily with conventional 
paint systems of normal thickness, and it is usually recom mended that they should be featured, e.g. by using 
bevel -edged boards or cover strips.  
 
Plasterboard dry -lining systems employ tapered -edge boards, enabling a smooth, seamless surface to be 
obtained by taping and filling the shallow trough formed by abutti ng edges. The process can be carried out 
manually or mechanically. It is possible that if a standard decorative paint is used directly onto dry lining, that 
a textural difference will be seen between the caulked and sanded joints, and the paper  plasterboa rd 
surface. Slurry  coats  and  purpose made  primers  can  be  used  to  assist  in disguising the difference in 
texture, and will also aid to even out the porosity of the substrate prior to painting.  
 
NOTE  Recommendations for internal plastering are give n in BS 5492. Recommendations for dry lining and partitioning using gypsum 
plasterboard are given in BS 8212.  
 
8.12.3.3   Priming  
 
Water -borne paints are usually applied direct to paper and other wallcoverings the exception being that a 
purpose designed pri mer should be used when there is a risk of discoloration on existing coloured 
wallpapers.  
 
8.12.3.4  Finishing  
 
Paper, vinyl, hessian and woven glass fibre surfaces are usually coated with water -borne paints. For 
improved wear resistance, acrylic water -borne paint should be used.  
 
8.13 Plastics  
 
8.13.1  General  
 
Typical examples of plastics in buildings include unplasticized polyvinyl chloride (PVC -U) cladding, rainwater 
goods and window frames; glass reinforced polyester (GRP) cladding and mouldings; and a variety of 
plastics coatings for metal.  
 
These materials generally have good durability, but the effects of weathering, soiling and mechanical 
damage  over  a  number  of  years  might  suggest painting  as  a  means  of  restoring the  or iginal 
appearance. Occasionally, premature deterioration occurs, and painting can then prove cheaper than 
replacement or, in the case of plastics coatings, can be necessary to prevent deterioration of the substrate. 
However, probably the most frequent reas on for painting is to change the colour, especially with 
components, such as PVC -U rainwater goods, available in a very limited range of colours.  
 
NOTE  For more detailed information, see BRE Information Paper 11/79 [19].  
 
If painting is considered as a met hod of restoring defective or deteriorated surfaces, specialist advice should 
be sought.  
 
Other plastics surfaces that might need painting for decorative purposes are expanded polystyrene and vinyl 
wallcoverings.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    85 8.13.2  PVC-U components  
 
Painting new unpl asticized polyvinyl chloride (PVC -U) with certain types of building paints can reduce the 
impact resistance. Specialist coatings have been developed and should be used to introduce new colour or 
rectify discoloration if it occurs. On ageing, PVC -U becomes brittle, abrasion of new PVC -U also reduces its 
impact resistance and should be avoided. Surfaces, new or weathered, should be prepared for painting by 
washing with warm detergent solution, rinsing with clean water and drying.  
 
In addition to specialist co atings, PVC -U can be painted with some water -borne paints, which have been 
formulated to have good adhesion. Manufacturer's recommendations should be followed. PVC - U should not 
be painted in a colour significantly darker than its  original colour otherwis e heat absorption is increased if 
exposed to direct sunlight.  
 
Pahits   of  conventional type  can  perform  satisfactorily on  PVC -U,  but  subsequent  maintenance painting 
at intervals of 3 years to 5 years might be necessary, thus negating an important a dvantage of plastics, i.e. a 
reduction in the frequency of maintenance. This might not be of significance where the areas are small and 
adjacent surfaces of traditional materials require maintenance painting at relatively short intervals. However, 
consider ation should be given to the use of long -life coatings on large areas such as cladding. Long -life 
coatings are usually of specialist type, e.g. two -pack polyurethanes or epoxies, but specialist advice should 
be sought.  
 
8.13.3  GRP components  
 
Most paints can be used on glass reinforced polyester (GRP) components. Surfaces should be prepared by 
thorough scrubbing with warm detergent solution and a stiff bristle brush or nylon pad (not wire wool, which 
can cause rust stains) followed by rinsing and drying. F or heavy contamination, a proprietary degreasing 
solution might be needed.  
 
As with PVC -U, consideration should be given to the maintenance aspects of painting GRP and the use of 
long-life coatings in certain circumstances. Although GRP is less sensitive t o solar gain than PVC -U, the use 
of light -coloured finishes is recommended.  
 
8.13.4  Plastics coated metal  
 
8.13.4.1  General  
 
A wide variety of organic coatings, classifiable as plastics, are used on metal cladding and other 
components. These can be overcoated (post -applied coating) for aesthetic or maintenance purposes at or 
near end of life. The individual types vary  and include polyvinyl chloride (PVC) plastisol, polyvinylidene 
fluoride (PVF2 or PVDF), polyester and polyurethane. Powder coatings s uch as epoxy, polyurethane, 
polyester or silicone modified versions are also found.  
 
It is essential that the pre -coating be identified to enable the application of a correctly adhering overcoating 
system, to be applied with or without a primer. Visual ide ntification is not straightforward, but older PVC 
exhibits a characteristic ripple and polyester can be glossy, the others all appear smooth and generally matt. 
Fourier transform infrared (FTIR) spectroscopy should be used to identify samples from site. Ma nufacturers 
provide information on suitable primers and top coat(s) and this should include provision for painting any 
bare metal, e.g. edges or patches.  
 
8.13.4.2  Identification  
 
When identification is not possible, a site adhesion test should be undert aken with the range of primers 
available and also a direct application. The test should be done on cleaned areas and in accordance with the 
coatings and the manufacturer's instructions.  
 
NOTE  This might involve leaving the overcoating systems for up to 7 d ays to allow adhesion to develop via plasticizer linkage on 
PVC for example.  
  
86  © KEBS 2018 — All rights reserved  Adhesion should be determined by the cross cut peel test in accordance with BS EN ISO 2409 or the pull off 
test in accordance with BS EN ISO 4624, or by instruments, such as a pu ll-off adhesion tester, the adhesion 
figure should be in excess of 1 N/mm2.  
 
8.13.4.3   Surface preparation  
 
Good surface preparation is vital and varies depending on the condition and typ e of the existing finish. a) All 
surfaces deemed to be in good condit ion should be powerwashed to remove all dirt, debris,  growths and 
erosion by -products. Grease and oil should be removed with a suitable cleaner  (soap or detergent) and all 
traces of cleaner need to be removed by rinsing.  
 
b) All loose, flaking and delamina ting coatings should be removed by either mechanical means, e.g. 
powerwash or hand preparations, or chemical means, e.g. paint stripper. Ensure all traces of chemical 
treatment are removed. Disbonding sections of PVC plastisol should be cut back to soundly  adhered 
material.  
 
c) Rusted areas should be prepared by removal of coating, oxidation products, dirt and debris, and 
abraded or blasted to, e.g. Sa2'/2, and should be primed before re -oxidation occurs.  
 
d) Severely corroded panels should be replaced either wholly or sectionally, small areas can be 
repaired using a permanent filler.  
 
e) Prior to priming/coating, areas which have been subject to mould growths should be identified and 
treated with a biocidal wash.  
 
8.13.5  Expanded polystyrene  
 
Expanded p olystyrene is used in tile or sheet form as a ceiling or wall lining and for decorative applications to 
improve thermal insulation. Wall linings are generally employed as a base for wallcoverings, but ceiling tiles 
and cornices can be painted.  
 
Paint solve nts attack expanded polystyrene. Painting of expanded polystyrene wall and ceiling linings should 
be with water -borne paints.  
 
WARNING!   Paints containing solvents, especially gloss finishes, can create a fire hazard when used in 
conjunction with expanded polystyrene.  
 
8.14 Glass and inorganic glazed surfaces  
 
8.14.1  General  
 
In addition to glass, materials in this category include glazed bricks, terracotta, faience, ceramic tiles and 
vitreous enamel. They are painted in some circumstances, e.g. to obscure clear glass or to renovate glazed 
surfaces or change their colour.  
 
A general characteristic of the surfaces relative to painting is that they provide little mechanical key, and this 
cannot usually be improved significantly by abrasion. Reliance has theref ore to be placed on the inherent 
adhesive properties of the paint, and this can vary according to type and composition.  
 
 
The painting of extensive or prominent areas should be undertaken only after consultation with the 
manufacturer, especially if the su rfaces are exposed to weather or high humidity or are subject to abrasion; if 
possible, evidence of satisfactory performance hi similar conditions should be obtained.  
 
8.14.2  Coating systems for glass and inorganic glazed surfaces  
 
8.14.2.1 Surface preparation  
 
Surfaces should be perfectly clean and dry at the tune of painting. It is recommended that surfaces are 
washed with detergent solution, followed by rinsing with clean water. Where external surfaces are greasy, 
solvent cleaning may be necessary  (see 7.4.1). On vitreous enamel, abrasion with waterproof adhesive KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    87 paper, while the surfaces are wet, can help to improve adhesion. Faulting should follow cleaning as soon as 
the surfaces are dry. If there is a delay, surfaces should be wiped with a clean  cloth and methylated spirits 
immediately before painting.  
 
8.14.2.2  Priming  
 
Finishes are often applied directly to glass and glazed surfaces, but the paint manufacturer's 
recommendations in this respect should be followed. Some multi -colour finishes (7/ 14) are applied over a 
bonding primer. Where damage or deterioration of vitreous enamel has exposed O the metal substrate, the 
exposed metal substrate should be primed.  
 
8.14.2.3   Finishing  
 
In the interiors of buildings, glazed bricks and ceramic tiling a re the surfaces of this type most likely to need 
painting. Multi -colour finishes are used fairly widely and should be applied in accordance with the 
manufacturer's recommendations. Alkyd gloss and mid -sheen finishes and one -pack polyurethane finishes 
can a lso be used and should be applied directly to the surface. Chlorinated and acrylated rubber  finishes  
should  be  considered,  especially  for  conditions  of  high  humidity  or  where condensation occurs. Some 
water -borne paints can be suitable in dry c onditions and are used to provide temporary shading on glass, 
however specialist coatings are available for this purpose.  
 
External surfaces should be treated as for internal surfaces but reference should be made to the 
manufacturer's instructions.  
 
None o f the conventional types of paints have the durability and resistance to wear of the original surfaces, 
and, where these properties are important, consideration should be given to the use of long - life specialist 
coatings which also have good adhesion, e.g . some two -pack polyurethane and epoxy types. The 
manufacturer should be consulted regarding the choice of materials and systems.  
 
8.15  Bituminous surfaces and materials  
 
8.15.1  General  
 
Surfaces and materials in this category include bituminous paints an d coatings, some preservative 
treatments and asphalt surfaces.  
 
These surfaces should not be painted with solvent -borne paints since there is a tendency for these surfaces 
to discolour them (bleeding) and sometimes to retard their drying. Cracking of appli ed paints might occur with 
some bituminous substrates.  
 
8.15.2  Bituminious paints and coatings  
 
Thin, hard coatings, especially when they are aged, can be primed before they are overpainted with solvent -
borne paints using, for example, an aluminium primer (3/5). Water -borne paints should be applied directly 
without a primer or sealer (some water -borne masonry paint systems include a bituminous emulsion 
basecoat as a waterproofing membrane for porous external walls).  
 
Paints  applied  over  thick  bituminous   coatings  might  crack  and  craze,  and  the  cracks  can 
subsequently  extend  into  the  underlying  material.  If  removal  of  the  bituminous  coating  is 
impracticable, it should be overcoated with material of similar type, e.g. tar paint or bitum inous aluminium 
paint.  
 
8.15.3  Preservative treatments  
 
NOTE  The use of creosote is prohibited, except for some industrial applications.  
 
Bituminous preservatives can be used for wood and some types of fibre insulating boards. Existing 
creosoted wood can generally be painted if it is has weathered for a year or more and is then primed with 
aluminium primer (3/4). A primer of this type should  also be used on fibre insulating board impregnated with  
88  © KEBS 2018 — All rights reserved  bituminous preservative, if it is to be painted with solvent -borne paint; water -borne paints can usually be 
applied directly to the board.  
 
8.15.4  Asphalt and bitumen  
 
Light -coloured finishes for asp halt and bituminous roofing materials should be used to reduce heat 
absorption and improve appearance. Particular care in the selection of coatings is essential, as unsuitable 
types can crack, as described in  8.15.2, resulting in serious damage to the roo fing material. Because of the 
ponding effect that can occur on flat roofs, it is also necessary for applied coatings to have good resistance 
to moisture to prevent loss of adhesion. Sand -rubbing of new asphalt is recommended to avoid the formation 
of a bit umen rich surface. The sand -rubbed surface assists the adhesion of coatings but the surface should 
be swept to remove excess sand before application. Specialist coatings are available for use on asphalt and 
bituminous roofing materials, and reference shoul d be made to the manufacturer for specific 
recommendations, based on experience.  
 
Quick -drying road marking paints, resistant to discoloration, should be used for marking asphalt roads, 
parking areas and factory -floors. Light -reflecting solid glass beads a re incorporated in some types or can be 
applied to the surface while the paint is wet.  
 
9 Application and practice  
 
9.1 Conditions of application  
 
9.1.1   General  
 
The application and performance of coatings are affected by the conditions under which they are applied, 
e.g. of temperature, humidity and general exposure conditions. The influence of these and other factors is 
described hi 9.1.2 to 9.1.7.  
 
9.1.2  Temperature and humidity  
 
Temperature and humidity will have an effect on the drying behaviour of mo st coating types.  
 
NOTE 1  See Annex L for information on temperature and humidity.  
 
The manufacturer's recommendations in respect of temperature and its relation to curing tune and pot life 
should be observed, especially in the case of specialist coatings such as two -pack epoxy and polyurethane 
coatings.  
 
In specifying the conditions under which coatings are to be applied, a general recommendation is that 
application should not start or should stop if the ambient temperature is below the manufacturer's 
recommendations (typically 8 °C or relative humidity exceeds 80%). In addition to the ambient temperature, 
a critical factor might be that of the surface to which the coating is applied. The temperature of heavy metal 
sections or  plates, as  well as plaster, rendering and masonry, for example, can be several degrees lower 
than the ambient temperature, especially early in the day.  
 
NOTE 2  In some circumstances, this general recommendation can be unduly restrictive and cause unnecessary delay or interruption 
of work. By agreement between the parties concerned, and having regard to the nature of the work and the types of materials  inv olved,  
some  relaxation  of  the  recommendations  in  respect  of  temperature  and  relative  humidity  might  be acceptable. So lvent -borne 
coatings, for example, can be less seriously affected than water -borne paints if applied in cold, damp conditions; application of primers 
and undercoats might be possible in conditions which preclude the application of finishes.  
 
Any agreed re laxation of the specified conditions should, however, be subject to the provisos that:  
 
A coatings are not be applied to surfaces on which condensation is present;  
 
b) coatings are of types reasonably tolerant of the prevailing conditions of application;  
 
c) records are kept of the occasions when relaxation is permitted.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    89 In assessing conditions of application, account should be taken of changes in temperature and relative 
humidity that are likely to occur within a few hours of application, and especially t he effects of overnight frost 
or high humidity on recently applied coatings (see 9.1.7).  
 
9.1.3  Surface moisture  
 
Adhesion, drying and other properties are nicely to be adversely affected if coatings are applied to wet 
surfaces. Application should not proceed when, as a result of adverse weather, high humidity or other cause, 
there is a visible film of moisture on the surface.  
 
Condensation is often a problem in unheated buildings during the winter months. Temporary heating 
equipment can help, but it is  important that heating be combined with adequate ventilation otherwise the 
problem can be aggravated. Portable gas and oil heaters produce water and should be used only if they are 
provided with means of exhausting combustion products to the outside of th e building.  
 
In some circumstances, e.g. when painting heavy metal sections, it might be necessary to delay application 
when the temperature of the surface is below the dew point of the air because of the risk of condensation, 
even though it has not yet oc curred.  
 
When conditions improve, wet surfaces should be dried off, and tune should then be allowed for contained or 
trapped moisture to dry out. This is especially important with absorbent surfaces but it is also applicable to 
rough metal including metal -sprayed surfaces. Prepared iron and steel surfaces that have not received a 
priming coat should be prepared further if rusting has occurred.  
 
9.1.4  Atmospheric pollution  
 
In industrial situations, fumes can retard the drying or cause discoloration of  conventional coatings; in severe 
cases, it might be necessary to use modified or specialist coatings, and the manufacturer should be 
consulted.  
 
The adhesion and drying of coatings might be impaired by the deposition of contaminants, including salt in 
marine situations. Where this occurs, surfaces should be cleaned thoroughly before application of each coat, 
and intervals between coats should be as short as possible.  
 
The effects of fumes and deposition of contaminants are likely to be most severe in foggy  weather and in 
conditions of high humidity.  
 
9.1.5  Air movement and wind  
 
Adequate movement of air assists drying and is essential to the removal of solvent vapours which can be 
unpleasant or potentially toxic or inflammable, especially when work is carri ed out in confined spaces; the 
manufacturer's recommendations in this respect should be strictly observed.  
 
Painting should be avoided under windy conditions unless precautions are taken, because the wind can 
carry dust and grit on to wet paint and mar its  appearance.  
 
Precautions should be taken in the use of spray equipment externally in windy weather as paint droplets can 
be carried for considerable distances, causing damage or annoyance.  
 
9.1.6  Lighting  
 
Good lighting is essential to efficient working.  Where natural daylight is lacking, an adequate level and type 
of artificial lighting should be provided.  
 
The lighting whilst painting should simulate, as far as practicable, the final lighting scheme in intensity and 
direction of lighting.  
 
NOTE  Informat ion concerning suitable illumination for differing purposes is given in the CIBS Code for interior lighting [20].  
  
90  © KEBS 2018 — All rights reserved  For most painting operations, 500 lux should be used. Higher levels, e.g. 750 lux, should be used for darker 
colours and inspection purposes.  For colour matching, limited contrast between coats or areas, and fine 
detail work, 1 000 lux might be necessary.  
 
Where the two higher lux levels are necessary and where colour perception in artificial light can be variable, 
illumination by lamps of colo ur groups 1A or IB of the CIBS Code for interior lighting [20], should be used; 
these include north light or artificial daylight types.  
 
NOTE  Examples of suitable bulbs and tubes are referred to in the CIBS Code for interior lighting [20].  
 
9.1.7  Seasonal factors  
 
If exterior painting is undertaken hi conditions when overnight frost or condensation is likely, the application 
of gloss finishes and water -borne coatings should be tuned to allow a reasonable period for drying before 
nightfall, otherwise their a ppearance or film properties might be unpaired. Surfaces, which are damp as a 
result of overnight conditions, should be dried before coatings are applied (see  9.1.3).  
 
NOTE  For further information on seasonal factors, see Annex L.  
 
9.2 Craft procedures and  practices  
 
9.2.1  Condition of surfaces  
 
Surfaces should be in a fit condition to allow work to proceed without detriment to the coatings to be applied. 
In some circumstances additional time is needed for drying out. Work by other trades that might affect 
painting should have been completed. If some tune has elapsed since preparation of the specification, any 
change  in  the  nature  or  condition  of  the  surfaces,  that  might  necessitate modification of the 
specification, should be drawn to the attenti on of the specifying authority.  
 
Factory -primed components should  be  inspected  to  ensure  that  the  condition  of  the  primer  is 
satisfactory; if it is not, remedial action should be taken (refer to the relevant substrate in Clause 8).  
 
9.2.2  Protec tion and cleanliness  
 
Surfaces not intended to be coated, including floors, furniture and factory -finished components and fittings, 
should be protected against splashing and spilling of painters' materials or other damage. As far as possible, 
door furnitur e, light fittings and similar items should be removed.  
 
Dust and dirt should be removed before painting otherwise the appearance and performance of coatings can 
be impaired. Where a high standard of finish is required, especially with gloss finishes, a tac k rag might be 
used to finish off the cleaning.  
 
Tools and equipment should be kept clean while in use and, where appropriate, cleaned immediately after 
use. Thorough cleaning after use is especially important with spraying equipment as residues of materia ls 
previously used can affect later applications or impair the efficiency of the equipment.  
 
Debris and waste material should be disposed of promptly and not allowed to accumulate in the working 
area. Safety precautions should be observed in the disposal of waste materials (see B.1 and B.3).  
 
NOTE  For recommendations in respect of personal hygien e and cleanliness, see Annex B.  
 
9.2.3  Abrasion  
 
Surfaces should be abraded (rubbed down) to reduce roughness, improve paint adhesion or assist cleaning. 
The types of abrasive materials in general use are as follows.  
 
a) Glasspaper can be used either dry o r with white spirit as a lubricant for the abrasion of wood, plaster 
and similar surfaces to improve adhesion of paint to non -ferrous metals (see 8.4.2.7). It can also be used to 
abrade painted surfaces, provided the paint is not lead -based, but wet - abras ion is more effective.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    91 b) Waterproof abrasive paper can be used wet or dry and is more effective than glasspaper for 
abrading painted surfaces. It should be used wet when abrading surfaces painted with lead - based paint 
(see B.I.2).  
 
c) Open -coated abrasi ve paper has the abrasive coating (typically aluminium oxide or  silicon carbide) 
sparsely distributed on the paper backing to reduce clogging. It should be used in mechanical sanding 
machines.  
 
d) Emery cloth or paper can be used either dry or with white spirit as a lubricant in preparing metals, 
especially non -ferrous metals (see 8.4.2.7) for painting.  
 
e) Steel wire wool has general application for abrading and cleaning. If used in the preparation of 
aluminium for painting (see 8.4.2.3), only stainless s teel wire wool should be used. Care should be taken in 
the removal of broken strands of wire wool from surfaces before painting or they can cause rust -spotting or 
discoloration. Protective gloves should be worn when using wire wool.  
 
f) Nylon fibre pads ca n be used instead of wire wool for some purposes (see 8.4.2.3).  
 
Abrasives should be of types and grades appropriate to their function and the nature and condition of the 
surface. Unduly coarse grades can cause unsightly scoring and scratching which shows through the finish. 
Care should be taken not to damage thin metallic coatings, e.g. thin films of aluminium on composite sheets. 
Care should also be taken to avoid damage to mouldings, arrises and similar features. If abrasion between 
coats is necessary, i t should be done lightly wit h fine, preferably part - worn, abrasive paper  to  avoid  tearing 
or  cutting through the  coating. For  hand -sanding of  flat surfaces, abrasive papers should be used in 
conjunction with a rubbing block.  
 
Dust and debris result ing from abrasion should be carefully removed and disposed of. For surfaces which 
have been dry -abraded, dusting or vacuum -cleaning should be undertaken; washing might be necessary. 
Surfaces that have been wet -abraded should be rinsed with clean water and wiped dry. On absorbent 
surfaces, tunes should be allowed for drying out before coatings are applied.  
 
9.2.4  Stopping and filling  
 
9.2.4.1   General  
 
Stopping and filling should be carried out as early in the coating process as the type of material used and  the 
nature of the substrate allow. Most materials used for stopping and filling are absorbent and, if applied late in 
the system, e.g. immediately beneath finishing coats, can cause sinkage and variations in gloss, sheen or 
colour. It should be noted that , if overall filling of surfaces is required, this should be clearly indicated in the 
painting specification.  
 
NOTE 1  The materials in general use for stopping and filling are described in 7.4 -4, and appropriate usage for substrates is indicated 
in Clause 8. 
 
NOTE 2  The term stopping or stopping -up relates to nail and screw holes, open joints, cracks and similar local cavities and deep 
depressions, while filling implies overall smoothing and levelling of shallow depressions and rough, open -textured or coars e-grained 
surfaces.  
 
9.2.4.2  Stopping  
 
The materials used for stopping are usually fairly stiff in consistency and are generally applied with a putty 
knife or stopping knife. The stopper should be pressed firmly into cavities in order to drive out air, w hich can 
prevent proper levelling. It should be knifed flush with the surrounding surface and not allowed to spread 
beyond the cavity. Deep cavities might require stopping in two stages, allowing an interval for the first 
application to harden. Nail and sc rew heads should be adequately countersunk for stopping, with heads 
normally not less than 2 mm below the surface.  
 
When drying -oil/resin stoppers are used, surfaces should be primed and the primer allowed to dry before 
stopping. This prevents absorption o f the binder from the stopper which might cause it to shrink and fall out. 
Priming is not usually required prior to the use of water -borne and powder fillers.  
  
92  © KEBS 2018 — All rights reserved  9.2.4.3  Filling  
 
Depending upon their type and consistency, fillers can be applied with a wide,  flexible filling knife or spreader 
or by brush. On broad surfaces, filling knives or spreaders are generally used, brushes being used for 
mouldings.  
 
Drying -oil/resin fillers are usually applied after priming, but some can be suitable for direct applicati on to 
unprimed surfaces; the manufacturer's recommendations in this respect should be followed. Water - borne 
and powder fillers can be applied to unprimed surfaces but, on absorbent surfaces, priming might be 
necessary to facilitate uniform spreading.  
 
Skilled application of fillers by knife or spreader should leave a surface, which requires little subsequent 
treatment, but some abrading might be necessary for final levelling. With drying -oil/resin fillers, waterproof 
abrasive paper (see 9.2.3), with water as a lubricant, can be used. Water -borne and powder fillers should be 
abraded dry. After abrading, surfaces should be rinsed or carefully dusted to remove residues of filler. If the 
surfaces have been wetted, time should be allowed for drying before painti ng. 
 
9.2.5  Preparation of materials  
 
9.2.5.1  Stirring  
 
Unless the manufacturer's instructions state otherwise, painting materials should be stirred before use and at 
intervals during use. The solid constituents in liquid paints can settle during storage a nd their re -
incorporation is essential to avoid defects such as poor opacity and retarded drying. Manual stirring is the 
method generally used for small quantities. A broad -bladed stirrer, long enough to reach the bottom of the 
container, should be used, a nd stirring should continue until no settlement remains. Mechanical equipment 
for stirring or shaking paint is available, and its use is advantageous when large quantities are involved.  
 
Thixotropic coatings (see 7.2) should not normally be stirred before use, except possibly for roller or spray 
application; stirring or shaking temporarily impairs the thixotropic properties.  
 
To avoid aeration and incorporation of any sediment, clear coatings are not usually stirred before use, but 
the manufacturer's instructions in this respect should be followed. Two -pack clear coatings should be stirred.  
 
9.2.5.2  Thinning  
 
Most of the coatings generally used in the painting of buildings, with the possible exception of some water -
borne paints, are supplied ready for  application by brush or roller. Water -borne paints could be supplied 
ready for use, but some need the addition of water. Thinning of primers might be necessary to improve 
penetration or facilitate application, e.g. on surfaces of high or variable porosity . Thinning might also be 
necessary for spray application of coatings. To prohibit thinning absolutely, as some specifications require, 
can be unreasonable, but it should be carried out only under supervision and with the types of thinners and 
in the propor tions recommended by the manufacturer.  
 
9.2.5.3  Intermixing  
 
Different brands or types of paints should not be intermixed without reference to the manufacturer.  
 
9.2.5.4   Two-pack materials  
 
Two-pack materials are supplied as two components, e.g. base and  activator, hardener or curing agent, to 
be combined before use. Base and activator can be held in separate containers or in a dual - pack container; 
in either case, the components are present in the correct proportions in relation to the total quantity of 
material supplied; if a small quantity is required, it should be measured to ensure that the correct proportion 
of each component is used.  
 
Some two -pack materials require an induction period (standing time) after mixing and before they are ready 
for use. Most have a limited pot -life (i.e. length of time during which they are usable), and this is temperature -
dependent. The manufacturer's instructions in relation to induction period and pot -life should be observed.  
 
9.2.6  Differing colours  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    93  
The manufacturer' s recommendations in respect of the colours of undercoats and first -coat colours should 
be observed. Wherever practicable, successive coats in paint systems should differ in colour. This assists 
application of continuous coats of uniform thickness, especia lly in conditions of poor lighting, and also 
facilitates inspection.  
 
Batch to batch colour variations might occur and it is therefore recommended that paint be bought from the 
same batch to ensure good colour consistency. If this is not possible, batches should be combined or mixed 
in a single container.  
 
9.2.7  Intervals between application of successive coats  
 
Generally, each coat in the system should be dry throughout its thickness before the next coat is applied. As 
indicated in 9.1, atmospheric conditi ons can affect the rate of drying and, in consequence, the interval 
between coats; it should not, in any case, be less than the minimum recommended by the manufacturer. 
Some coatings might be suitable for wet -on-wet application, i.e. a second coat can foll ow immediately.  
 
Except with coatings formulated for lengthy exposure without further coats, such as some primers for metal 
and wood (see appropriate substrate in Clause 8), intervals between coats should not normally exceed a  
few days, otherwise adhesion  might be impaired. With some specialist coatings, the manufacturer might 
specify a maximum time to be allowed between coats.  
 
 
9.2.8  Intercoat preparation  
 
It should be ensured that the surface is clean before application of each coat in the system. This is important 
if there has been a lengthy interval between coats especially in situations where contamination of the surface 
is likely, e.g. in marine or industrial environments.  
 
Except when the previous coating has become very hard, as a result of lengthy  exposure, vigorous abrasion 
between coats is rarely necessary to assist intercoat adhesion. Light scuffing with fine - grade, preferably 
part-worn, abrasive paper is sufficient to remove nibs and adherent dust particles, but care should be taken 
not to scr atch or tear the coating; if this occurs or the abrasive paper rapidly clogs, it is an indication that the 
surface is not sufficiently hard to permit abrasion.  
 
If extensive flatting of a previous coat is necessary to assist adhesion or provide a smooth le vel surface, wet 
abrasion, with waterproof abrasive paper and water, is usually the most effective method, but the coating 
should be hard before it is attempted.  
 
9.2.9  Defective materials  
 
If, during the course of the work, it appears that the material mi ght be defective, no more should be applied 
until the matter has been investigated by the manufacturer or supplier. To continue to apply material which 
might be defective can involve additional costs for which compensation could not justifiably be claimed from 
the manufacturer or supplier even if the material proves to be defective.  
 
9.3  Application methods  
 
9.3.1  General  
 
The principal methods of applying coatings on site are by brush, roller, paint pad and paint glove and spray.  
 
Choice of method should be determined by the nature of the work or the type of material to be applied. The 
manufacturer's recommendations regarding the suitability of coatings for application by particular methods 
should be followed.  
 
Whatever method is employed, operatives shoul d be skilled and experienced in the techniques of 
application, as well as in the care and maintenance of tools and equipment and, where relevant, in the 
setting up and adjustment of equipment to obtain optimum results.   
94  © KEBS 2018 — All rights reserved   
9.3.2  Brush application  
 
9.3.2.1   Characteristics  
 
Brushing can be used for the application of most coatings of conventional type, especially to small areas or 
where there is much cutting -in or frequent changes of colour. It is also generally recommended for  the  
application of  conventi onal types of  primers to  building surfaces, on  the principle that the shearing action 
of brushing forces the coating into intimate contact with the surface, although suitable types of rollers can be 
equally effective in this respect.  
 
With some exceptio ns, multi -colour finishes (7/15) cannot be applied by brush and should be sprayed. 
Difficulty might be experienced in the brush application of quick -drying coatings, especially to large areas. 
For these and for some specialist coatings, spray application i s preferred.  
 
Brush application to large, unbroken areas is slower than roller, paint pad or spray application and it is more 
difficult to obtain a uniform coating.  
 
9.3.2.2  Types of brushes  
 
The construction and dimensions of brushes should conform to BS  2992. For most purposes, brush fillings 
should be pure bristle, good quality mixed bristle or synthetic filaments. Synthetic filaments are harder 
wearing than natural or animal hair and should be used when working with caustic materials such as cement 
paints, but their material -holding properties might be slightly inferior.  
 
NOTE  Flat paint and varnish brushes, suitable for general use, range in width from 12 mm to 100 mm. Flat wall brushes, used mainly  
for application to broad surfaces such as walls and c eilings, are from 100 mm to 175 mm wide. Small fitches for narrow surfaces and 
decorative work are from 6 mm to 25 mm in width or diameter.  
 
In selecting appropriate sizes of brushes, the general principle should be to use the largest sizes consistent 
with application of a uniform coating without undue effort. Apart from any constraints imposed by the extent 
or nature of the surface to be coated, generally smaller brushes should be used with more viscous materials, 
such as solvent -borne gloss finishes, rath er than with those which offer little resistance to brushing, such as 
water -borne paints.  
 
It  is  recommended that  synthetic filament  brushes are  used  for  the  application of  water -borne coatings. 
They do not absorb water to the same extent as natur al bristle brushes, and in consequence deliver a 
smooth, consistent application, improve the flow and wet -edge time of the coating material and hence reduce 
brush marks. Synthetic filament brushes are also much easier to clean.  
 
9.3.2.3  Basic techniques  
 
In general terms, the basic technique of brush application involves three phases. First, the material should 
be applied in a reasonably full coat and evenly spread, working most of it out of the brush and recharging as 
necessary. Then, without reloading th e brush, it should be drawn in one direction (crossed) and then at right 
angles to this in order to distribute the coating evenly and uniformly. Finally, the coating should be laid off, 
i.e. the brush is drawn lightly in the direction of the greatest lengt h of the work, in order to eliminate brush 
marks as far as possible.  
 
NOTE  This technique might require modification according to the nature of the surface or the type of coating being applied.  
 
Many undercoats and most finishes have good flow properties and, for final laying off, lighter pressure 
should be used. Repeated crossing and laying off is not usually practicable with quick -drying coatings which 
should be applied as quickly as possible with the minimum of brushwork; roller or spray application of this 
type of coating is usually preferred, especially for large areas. In applying matt and mid -sheen coatings to 
ceilings and walls, the material should be applied and laid off using criss -cross strokes (switching) rather 
than hi one direction.  
 
Over -heavy application of coatings should be avoided as this can cause runs and sags, particularly with free -
flowing materials such as gloss finishes and varnishes. With some types of coatings, a surface skin can form KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    95 which retards through drying. The oppo site extreme of brushing out too far should also be avoided as this 
produces excessively thin films having poor appearance or lacking in protective properties.  
 
Heavy accumulations of paint (fat edges) along edges and arrises should be avoided by brushing towards 
them rather than in the reverse direction.  
 
Application, especially to large areas, should be so organized that wet edges are maintained, i.e. that each 
section of the work is joined up to the preceding section before its edge has set, thus prevent ing unsightly 
laps. On large areas, the number of painters deployed should be sufficient to permit wet edges to be picked 
up with minimum delay. Where scaffolding is necessary, its arrangement should facilitate quick transfer from 
one section of the work t o the next.  
 
9.3.3  Roller application  
 
9.3.3.1  Characteristics  
 
The types of coatings described in 9.3.2 as suitable for application by brush are also suitable for roller 
application; the limitations in respect of certain types of coatings also apply. The  method is quicker than 
brushing on large, unbroken areas, such as ceilings, walls, flush doors, floors and plate work but is not 
recommended for small areas or where much cutting -in is required. A brush should be used to coat internal 
angles and corners, e.g. between ceilings and walls.  
 
Although brush application of conventional types of primers to building surfaces is usually recommended, 
some types of rollers have a similar shearing action and can be equally suitable.  
 
Rollers with appropriate roller co verings should be used for the application of coatings to rough or uneven 
surfaces, such as rough -cast external walls; for this purpose, they are usually quicker and more effective 
than brushes.  
 
NOTE  A degree of stipple or surface texture is characteristi c of coatings applied by roller but, if the appropriate type of covering is 
used, this can hardly be discernible, especially with free -flowing materials such as gloss finishes.  
 
9.3.3.2  Types of rollers  
 
Rollers should be of good quality and robust constr uction. Preferably, they should have interchangeable 
roller coverings which can be selected depending on the surface or coating.  
 
NOTE 1  Materials for roller coverings include various natural and synthetic fabrics and fibres. Coverings employing synthetic fibres are 
widely used; they are generally described in relation to the length of the fibres, i.e. as short, medium, or long pile types,  the length of the 
fibres ranging from about 6 mm to 30 mm.  
 
Short and medium pile types should generally be used for ap plication to smooth surfaces when it is 
necessary to avoid excessive stippling of the coating. Long -pile types should be used for application to 
brickwork, rough -cast and similar surfaces or when it is necessary to impart a texture to the coating. The 
roller or paint manufacturer's recommendations regarding the most suitable types of coatings should be 
followed.  
 
NOTE 2  For general use rollers about 200 mm wide are suitable, but larger and smaller sizes can be obtained. Special rollers are 
available for the  application of coatings to corrugated sheeting, pipes and curved surfaces. Many rollers, including the special types, can 
be mounted on an extension pole to extend the operative's reach.  
 
Rollers, other than the pressure feed types, should be charged by dipping the head of the roller into the 
material and then rolling it over a corrugated or coarse mesh surface to distribute the material evenly around 
the covering. Roller trays are designed for this purpose, but they hold only a small quantity of material , are 
easily overturned and are inconvenient for ladder work. Paint roller buckets should preferably be used, 
especially for large -scale work and when working from ladders; they are available in sizes holding 5 1 to 20 1 
of material.  
 
NOTE 3  Rollers are av ailable in which material is supplied from a separate container' under pressure. They are claimed to show 
considerable savings in time compared with the normal type of roller by eliminating the need to recharge from a tray or bucke t. In one 
type, material is supplied to the roller from an airless spray pump unit, via a flexible hose, the roller taking the place of the spray gun.  
Extension tubes giving a reach of up to about 2.5 m can befitted.   
96  © KEBS 2018 — All rights reserved   
9.3.3.3  Basic techniques  
 
Although it is probably easier to ob tain a film of uniform thickness by roller than by brush, judgement in 
respect of the weight of coat applied is still essential. In particular, excessive rolling -out with a dry roller 
should be avoided. As with brush application, work should proceed system atically in sections, and the same 
attention should be paid to the maintenance of wet edges (see 9.3.2.3) although, in this respect, the greater 
speed of roller application is an advantage.  
 
Where rollers cannot reach into corners and internal angles, brus hes should be used for cutting -in and this 
should be done immediately ahead of rolling, the roller then being taken as closely to the angle as possible.  
 
When it is required to eliminate the slight stipple that can be produced with roller application, as m ight be the 
case with undercoats for gloss finishes, a brush should be used for laying off immediately after rolling.  
 
9.3.4  Paint pads  
 
Paint pads consist of a layer of paint -holding material similar to that used for short -pile roller coverings (see 
9.3.3 .2) fixed to a rigid or flexible backing. The pad is held in a metal or plastics plate and can be fixed or 
replaceable. The plate is provided with a fixed or adjustable handle. Various shapes and sizes are available; 
the largest sizes are about 150 mm x 10 0 mm and can be suitable for attachment to an extension pole. 
Application by paint pad is faster than by brush but slower than by roller.  
 
In use, the pads should be charged by dipping the face of the covering into the paint and working it out on a 
corruga ted or mesh surface as with a roller. A roller tray or roller bucket should be used for this purpose. The 
charged pad should then be placed against the surface and drawn along, using moderate pressure.  
 
Where paint pads cannot reach into corners and intern al angles, brushes should be used for cutting -in and 
this should be done immediately ahead of application by paint pad, the paint pad then being taken as closely 
to the angle as possible. They can, however, produce a finish free from brush marks or stipple . 
 
Application by paint pad can be used for the following:  
 
a) ship-lap cladding;  
 
b) small areas that might not warrant putting a roller into use;  
 
c) panelled and flush doors;  
 
d) mouldings, picture rails and skirtings;  
 
e) metal window frames;  
 
f) wide lines and stripes.  
 
It is essential that paint pads be of good quality and robust construction.  
 
9.3.5  Paint gloves  
 
Paint gloves or gauntlets have an outer surface of sheepskin or fabric similar to that used for roller coverings. 
In use, the  gloved hand  should be clipped into the  material, which should then be transferred to the surface 
by wiping or dabbing. A sealed liner protects the hand, wrist and forearm against soiling with paint. They can 
be used to coat pipes, railings and surfaces which are ina ccessible to other methods.  
 
9.3.6  Spray application  
 
9.3.6.1 General  
 
There are several types of spray equipment, differing in method of operation and in the coatings and types of 
work for which they are suitable. In general, however, it can be assumed th at there is spray equipment 
available for the application of virtually every type of coating likely to be used for buildings and structures.  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    97  
Spraying can be used on large, unbroken areas where the nature of the work permits continuous working for 
lengthy periods enabling a speed of application which is faster than other methods of application. Spraying 
should not be used on small -scale work unless the coatings are of a type for which spray application is 
essential or preferred; brush or roller application can be more economic.  
 
Spray application is essential for most multi -colour finishes (7/14) and is preferred for coatings based on 
solution binders (e.g. 11/5), especially for application to large areas. Zinc -rich ep oxy primers (4/7) should be 
applied by spray, as should some specialist coatings. The manufacturer's recommendations regarding the 
preferred method of application should be followed.  
 
The following possible limitations to spray application should be taken into account.  
 
a) The need for extensive  masking or protection of surfaces not to be coated, although this is 
influenced by the type of equipment used.  
 
b) Possible hazards to health or safety (see Annex B).  
 
c) Spray application on exterior work in windy weather can cause difficulties as spray mist can be 
carried considerable distances and cause damage or nuisance. As in relation to a), the type of equipment 
used is a relevant factor.  
 
d) It is generally recommended that conventional primers for building surfaces not be applied by spray. 
Excepti ons to this include zinc -rich epoxy primers and some specialist types which might be unsuitable for 
application by brush or roller.  
 
Coatings and spray equipment manufacturer's recommendations on the selection and setting up of 
equipment and the preparatio n of materials should be followed and their guidance sought in cases of doubt.  
 
9.3.6.2   Types of spray equipment  
 
9.3.6.2.1  General  
 
The following types of spray equipment are in general use for the site application of coatings:  
 
a) air spray;  
 
b) airless spray;  
 
c) air-assisted airless spray.  
 
Modified forms of spray equipment include hot spray and electrostatic spray equipment, but these are not 
used to a significant extent for site work.  
 
9.3.6.2.2   Air spray  
 
In air spray equipment, air under pressur e is employed to atomize the coating and convey it to the surface. 
According to the design of the equipment, working air pressures range typically from about  0.20 MPa to 0.47 
MPa (30 lbf/in2 to 70 lbf/in2)  or more.  
 
Lightweight units operating at pressures  of 0.20 MPa to 0.27 MPa ( 30 lbf/in2 to 40 lbf/in2 ) should be used for 
decorative coatings. Larger units operating at higher pressures can be used for most types of coatings 
although airless spray application (see 9.3.6.2.3) might be preferred for some spe cialist types. Atomization is 
more effective with larger units than with lightweight units, enabling a higher standard of finish to be 
achieved. In addition, material throughput is higher, facilitating more rapid application.  
 
As all forms of air spraying give rise to spray mist (although this is less pronounced with equipment operating 
at lower pressures) surfaces that are not to be painted should be masked and, for interior working, the  
98  © KEBS 2018 — All rights reserved  provision of additional ventilation or means of extracting spray mist  from the working area might be 
necessary.  
 
If compressor units for air spray equipment are powered by a petrol or diesel engine, they should be located 
outside the building, if possible; if this is not practicable, exhaust fumes should be conveyed directl y to the 
open air.  
 
9.3.6.2.3   Airless spray  
 
In airless spray equipment, a fluid pump forces the material at very high pressure, typically 14.3 Pa to  21.4 
Pa (2 000 lbf/in2 to 3 000 lbf/in2), through a restricted orifice in the spray gun so that on releas e to the 
atmosphere the material immediately atomizes. Airless spray equipment is available in a wide  range of sizes 
and capacities, including small units weighing less than 45 kg (100 Ib).  
 
High rates of application can be achieved with airless spray equi pment, and the absence of atomizing air 
means that there is almost no spray mist and consequently little waste of material or necessity for extensive 
masking. Most types of coatings can be applied, possible exceptions being those containing coarse 
aggregat es or fibres, e.g. some masonry paints. Thicker films can be obtained than with air spray equipment, 
and should be used in particular for the application of high -build specialist coatings.  
 
With some types of airless spray equipment, a separate source of c ompressed air is required to operate the 
fluid pump. When this is supplied by a compressor powered by a petrol or diesel engine, precautions in 
respect of exhaust fumes as described hi 9.3.6.2.2 should be taken.  
 
Because of the very high pressures involved , caution should be exercised in the handling of airless spray 
equipment; in particular, the spray gun should never be pointed towards any part of the body while the 
equipment is in operation.  
 
9.3.6.2.4 Air -assisted airless spray  
 
Air-assisted airless spr ay equipment combines some of the characteristics of high -pressure air and airless 
spray methods. A pump unit of similar type to that used for airless spray is employed, but it operates at lower 
pressure, usually in the range 6.7 MPa to 12.0 MPa ( 900 lbf/i n2 to 1 700 lbf/in2 ). In addition, the spray gun is 
supplied with a small volume of air at low pressure. Air -assisted airless spray equipment allows the operator 
the same degree of control over application as does air spraying while having the freedom from  spray mist 
and economy in the use of coating associated with airless spray  
 
9.3.6.2.5   Hot spray  
 
In hot spray equipment, the material is passed through a heater unit before delivery to the spray gun. 
Heating enables high viscosity, low solvent (or solven t-free) coatings to be applied by spray to give a thicker 
film. Coatings need to be specially formulated for hot spray application; water -borne coatings should not be 
used.  
 
The hot spray method can be used in conjunction with either air spray or airless s pray equipment.  
 
9.3.6.2.6  Electrostatic spray  
 
Electrostatic spray method involves imparting to the material an electrical charge of opposite potential to that 
of the surface to be coated, causing the charged particles to be attracted to the surface. This reduces 
wastage of material and also creates a wrap round effect so that components such as pipes and railings can 
be coated all round from one direction. Using a special unit to impart a charge to the material, the method 
can, in principle, be used i n conjunction with air spray or air -assisted airless spray equipment for the 
application of coatings to structural surfaces. However, the electrical characteristics of the material and the 
surface to which it is applied are critical factors and, in practic e, electrostatic spraying has little application for 
site work although it is used widely in industrial finishing. If its use is considered, equipment and coatings 
manufacturers should be consulted.  
 
9.3.6.3  Basic techniques  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved    99 All  masking  and  protection   of  adjacent  surfaces  should  be  completed  before  spraying  starts. 
Elaborate masking might be unnecessary when airless spray equipment is used; because of the virtual 
absence of spray mist or over spray, it is often possible to cut -in by using a ha nd-held shield. If masking tape 
is used in spraying, it should be removed as soon as possible after completion of the work. It is advisable to 
cut along the edges of the tape with a sharp knife to prevent the coating film being pulled away with the tape.  
 
WARNING  Because of the very high pressures involved, caution should be exercised in the handling of 
spray equipment; in particular, the spray gun should never be pointed towards any part of the body while the 
equipment is in operation.  
 
Equipment should b e checked to ensure that it is in good condition and working efficiently. Spray guns 
should be of appropriate type and set up in relation to the material to be applied; reference should be made 
to the equipment or coating manufacturer's literature for guid ance in this respect.  
 
Coatings should be prepared for use as described in 9.2.5. It should not be assumed that coatings for spray 
application necessarily need to be thinned. Unless the manufacturer's recommendations are to the contrary, 
or experience sugg ests otherwise, a trial application of unthinned coating should first be made. If thinning is 
necessary it should not exceed the manufacturer's recommendations; if excessive amounts of thinner are 
required to facilitate application, it is likely that the e quipment is of unsuitable type or is not operating 
correctly.  
 
When spraying, the gun should be held at right angles to the surface, horizontally and vertically. In air 
spraying, the distance between the front of the gun and the surface should be 150 mm to  200 mm; in airless 
spraying, the distance should be 300 mm to 375 mm. These distances should be maintained as the gun is 
moved across the surface; i.e. it should not be swung or arced. Each stroke should be made at a constant 
rate to maintain a uniform th ickness of coating. The trigger of the spray gun should be pressed just before 
the start of each stroke and released just before it is completed. With air spray guns, the trigger movement 
should be gentle and progressive, but with airless spray guns it sho uld be firm and abrupt. Each stroke 
should overlap the previous one to ensure uniform coverage; usually, more overlap is required with air 
spraying than with airless spraying.  
 
10 Inspection, sampling and testing  
 
10.1 General  
 
Most painting work is subject to final inspection on completion; on major projects, the work should be subject 
to inspection (see 10.2) at all stages. Sampling and testing of materials (see 10.3) might be required.  
 
10.2 Inspection  
 
10.2.1  General  
 
Inspection should be carried out  to  ensure compliance with  the specification. It  should not  be considered 
as a substitute for proper supervision of the work by the contractor nor a means of compensating for an 
inadequate or incorrect specification.  
 
Inspection should also be carr ied out to ensure that acceptable standards of workmanship and quality of 
finish are achieved. It is often difficult to specify these in terms which preclude subjective judgement. Where 
possible, reference standards on representative areas should be used t o serve as a basis for tendering and 
inspection, but it is important to ensure that the standards set are realistic in relation to the system specified, 
the nature of the substrates and the conditions under which the work is to be done.  
 
The responsibility  for inspection should be independent from that for application.  
 
NOTE  On large projects, the employment of a specialist inspection organization might be justified; in other 
cases, inspection might be carried out by members of the specifying authority's st affer a clerk of works.  
 
Inspectors should have a good knowledge of the materials, processes and techniques employed in the 
painting of buildings.   
100  © KEBS 2018 — All rights reserved   
When  work is  to  be subject to  inspection, the intended procedure should be  described in  the 
specificat ion. It is important to ensure that resources are available to implement the procedure described, 
especially when the work is to be subject to inspection and approval at each stage (see 10.2.2 regarding 
levels of inspection). If the inspector is empowered to suspend work (or take comparable action) or take 
samples, this should also be stated in the specification.  
 
10.2.2  Levels of inspection  
 
Typical levels of inspection are as follows.  
 
a) Full. All operations are subject to inspection and approval before the next stage is started. This is the 
most effective level of inspection but is likely to require the services of one or more full -time inspectors and 
might be justified only on very large or complex projects.  
 
b)   Intermittent. Part of all operations is  inspected and approved be fore the next stage is started. This 
level of inspection is less effective than full inspection but is less demanding in terms of cost and resources 
and therefore more appropriate for smaller projects or work of a straightforward nature.  
 
c) Occasional.  All operations are subject to  inspection  initially  to  establish  standards  of 
workmanship. Thereafter, inspection is carried out as judged necessary by the inspector. The effectiveness 
of this level of inspection depends large ly upon the quality of supervision exercised by the contractor.  
 
The following factors should be taken into account when selecting the level of inspection appropriate to a 
painting operation:  
 
1)   the nature of the work and the functions of the coating sy stem: for example, normal maintenance 
redecoration work might not require full inspection, but this might be necessary for work involving the 
application of specialist coatings;  
 
2) the cost of inspection in relation to the value of the contract;  
 
3) the resources available for inspection, especially when several locations are involved;  
 
4) the quality of supervision likely to be exercised by the contractor.  
 
Ad hoc inspection of work in progress might be all that circumstances or resources permit. Although better 
than no inspection, it cannot be regarded as an effective method of ensuring compliance with the 
specification.  
 
In some circumstances, e.g. when work is of short duration, it might not be possible to do more than inspect 
the work on comple tion. This might suffice where finished appearance is the main criterion, but it does little 
to establish that the work specified has actually been carried out and, in particular, that the surfaces have 
been correctly prepared.  
 
10.2.3  Duties of the inspec tor 
 
The inspector should assess whether compliance with the specification has been achieved in all respects. 
The inspector's duties are not described here in detail but should include some or all of the following:  
 
a) ensuring that surfaces are in fit con dition for the application of coatings: this might include checking 
the moisture content of substrates;  
 
b) ensuring that preparatory work is carried out as specified and, where applicable, to agreed 
standards;  
 
c) ensuring  that  work  is  carried  out  u nder  suitable  conditions, e.g.  of  weather,  temperature, 
humidity, ventilation and illumination;  
 
d) ensuring that materials are of the types and makes specified and are properly stored;  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 101 e) ensuring that the specified number and sequence of coats are applied, and that application is in 
accordance with the specification or the manufacturer's recommendations: this might include checking film 
thickness;  
 
f) if so empowered, suspending work or taking comparable action when there are reasonable grounds 
for doing so, e.g. if conditions are unfavourable for painting: work should be stopped if it appears that 
materials might be faulty (see 9.2.9);  
 
g) taking samples for testing if this is a requirement of the specification or is necessary in order to 
investigat e apparent defects;  
 
h) drawing the attention of the client or specifier to any modifications to the specification which might 
appear necessary in order to achieve a satisfactory result;  
 
i) maintaining work records and preparing progress reports;  
 
j) where a separate painting schedule is provide, ensuring that all items are finished in the required 
colours and types of finish.  
 
10.2.4  Final inspection  
 
Whether or not work has been subject to stage inspection, it should be inspected on completion. In so me 
circumstances, as noted in 10.2.2, this might be the only inspection carried out. Final inspection should be 
made in the presence of the contractor or the contractor's representative. Arrangements should be made to 
inspect work which will subsequently b e inaccessible before removal of scaffolding. The main points on 
which the general quality of coating systems should be judged by visual inspection are as follows:  
 
a) where applicable, satisfactory stopping and filling: it should be clearly specified if o verall filling of 
surfaces to achieve a high standard of finish is required;  
 
b) uniformity of gloss, sheen or texture;  
 
c) with pigmented finishes, uniformity of colour and satisfactory hiding of the substrate or previous 
colour;  
 
d) freedom from conspic uous film defects such as runs, sags, wrinkling or fat edges; entrapped dust, 
dirt or paint skins; bare or starved areas; prominent brushmarks, roller stipple or spray mottle;  
 
e) freedom from tackiness;  
 
f) accuracy of cutting -in; 
 
g) general cleanliness,  with no soiling or disfigurement of adjacent surfaces.  
 
In assessing  the  general  quality  of  work,  the  significance  of  any  observed  defect  should  be 
considered in  relation to  the  functions of  the coating system. For  example, defects that  affect appearance 
might not be important where protection is the sole or essential function. Allowance should also be made for 
the influence of conditions or circumstances outside the control of the contractor, such as the condition of the 
substrate, whic h might be highlighted by low angle illumination (see also 9.1.6).  
 
10.3 Sampling and testing  
 
The routine sampling and testing of materials should be carried out if required for one or both of the following 
reasons:  
 
a) to ensure compliance by suppliers with specifications or stated requirements for materials;  
  
102  © KEBS 2018 — All rights reserved  b) as  a  safeguard  against  over -thinning,  adulteration  or  similar  undesirable  practices  during 
application.  
 
In either case, samples should be taken or set aside for examination by the spe cifying authority.  
 
For the reason indicated in a), samples should be in the original unopened containers. In respect of b), 
samples should be taken during application, e.g. from painters' kettles or spray -equipment containers. At 
least two samples should be taken, one for testing and one for the contractor; it might be a dvisable to take a 
third sample  for submission to the manufacturer should this subsequently prove to be necessary.  
 
Subsequent testing is generally the responsibility of the specifying authority, but the specification should  
define the  contractor's responsibility for  providing samples (including the  frequency and quantity of material 
to be provided) and describe to which standard the tests should be carried out.  
 
The coating should b e tested in comparison to a test sample against an agreed standard. This might be the 
manufacturer's specification for the material or a physical sample supplied by the manufacturer or taken from 
a previously unopened container after thorough mixing. If th ey are available, the batch numbers of materials 
used as standards or submitted for testing should be recorded.  
 
The paint should be tested in accordance with the relevant part of BS 3900. BS 3900 describes a 
comprehensive range of tests for paint under th e following general headings:  
 
Group A  Tests on liquid paints (excluding chemical tests)  
 
Group B  Tests involving chemical examination of liquid paints and dried paint films  
 
Group C  Tests associated with paint film formation  
 
Group D  Optical tests on pai nt films  
 
Group E  Mechanical tests on paint films  
 
 Group F  Durability tests on paint films  
 
Group G  Environmental tests on paint films (including tests for resistance to biological growth, 
corrosion and chemicals)  
 
Group H  Paint and varnish defects  
 
Most  of these tests require laboratory facilities and should be carried out by trained personnel.  
 
Where the measurement of flow time is tested in accordance with BS 3900 -A6, a minimum of 100 ml of 
material should be taken for testing. Where the thickness of a pplied paint films is to be measured, it should 
be in accordance with BS 3900 -C5. 
 
NOTE   For further guidance on protective coatings on structural steel, see BS EN ISO 129 44, and for 
concrete, see BS EN 1504 -10. 
 
11 Maintenance  
 
11.1 General  
 
The recommend ations given in ISO 12944 and BS 5493 should be followed for the maintenance painting of 
steel structures and those in BS EN 1504 -10 for concrete structures.  
 
NOTE 1  Recommendations on the maintenance painting of buildings can be found in 5.10.  
 
The genera l aim of maintenance in relation to coating systems should be to maintain or restore to a 
satisfactory standard the effectiveness of coating systems to their original functions (can include cleaning) at 
the lowest cost assessed on an annual basis.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 103 NOTE 2  Attention is drawn to statutory requirements or terms of occupancy which require that maintenance is carried out.  
 
Maintenance requirements should be considered at the design stage of new buildings.  
 
NOTE 3  Application  of  the  design  principles  referre d  to  in  Clause  4,  including  those  relating  to  access,  can  make  a 
considerable contribution to ease and economy of maintenance.  
 
Initial treatment of new substrates, as described in Clause 8, should be considered in relation to subsequent 
mainte nance requirements. Except possibly where the condition of substrates imposes restrictions on the 
selection of coating systems, as can be the case with wet substrates, the aim should be to use systems, 
which provide a sound base for further coats with the minimum of preparation.  
 
NOTE 4  Initial preparatory treatment is especially important as it can affect the performance of coating systems throughout the life  of 
the building. Some effective preparatory treatments, e.g. abrasive blasting of steelwork or preservative treatment of timber, can be 
difficult or impossible to carry out as maintenance operations.  
 
A planned approach should be adopted in order to achieve the aims of maintenance. An essential factor is 
the establishment of a maintenance schedule, for areas requiring regular treatment at intervals that 
experience and observation have shown to be the most economic and best suited to local conditions and 
specifications. The maintenance schedule should include provision for regular inspection and recor ding of 
the condition of coating systems so that their performance can be monitored and evaluated. This facilitates 
proper assessment of future requirements and enables adjustments to be made to the maintenance 
schedule, if this is found to be necessary. R ecords should also be kept of the details, including costs, of all 
maintenance treatments carried out.  
 
11.2 Factors affecting decisions on maintenance  
 
11.2.1  Timing and frequency  
 
In principle, maintenance should be carried out while the existing coating  is in sound condition, when little 
more than cleaning down and the application of the minimum number of coats needed to restore the original 
properties is necessary.  
 
NOTE 1   In practice, the condition after a given period of exposure is unlikely to be un iform over all 
parts of a building. Typically, some parts will still be in good condition when others require treatment; overall 
treatment at this stage might well be uneconomic. On the other hand, if deterioration is allowed to proceed 
too far, it is like ly that extensive preparation and possibly complete renewal of the system over large areas 
will be necessary. The additional cost of the work might then exceed any apparent saving made by delaying 
maintenance. Hidden costs might be incurred as a result of deterioration of structural materials, loss of 
production or revenue decline in amenity value and other factors.  
 
Buildings  should  be  regularly  inspected  and  the  findings  recorded  to  determine  the  optimum 
frequency of maintenance. Where experie nce or records are lacking, as they can be with new buildings, 
maintenance inspections should be carried out at relatively short intervals in the early stages.  
 
NOTE 2  If this can be implemented, a film of substantial thickness can be built up fairly quick ly, an important factor where the system 
has a protective function.  
 
11.2.2  Condition of paintwork  
 
The form and extent of any deterioration that has occurred influences the nature of the preparatory work 
necessary and, in many instances, the selection of coating types and systems (see 11.2.4). Its significance 
should be assessed in relation to the functional requirements.  
 
NOTE      For example, where the emphasis is on protection, forms of deterioration, which affect appearance 
alone, such as soiling, col our change or reduction in gloss, might have little significance. Conversely, most 
forms of deterioration affect appearance although they might not impair protective properties.  
 
Causes of deterioration should be investigated, unless they are obvious, so t hat corrective action can be 
taken (see 11.3).   
104  © KEBS 2018 — All rights reserved   
The more commonly encountered defects, typical causes and considerations in respect of remedial 
treatment can be found in Table 19 and Table 20, but where unusual or rapid deterioration is apparent, 
expert in vestigation and advice should be sought.  
 
11.2.3  Variability of deterioration  
 
Deterioration varies according to aspect, elevation, local exposure conditions, conditions of service and other 
factors and so specifications should be modified to allow for different forms of preparations or the application 
of additional coats. In some circumstances, patch -painting (see 11.2.7) should be considered.  
 
11.2.4  Structural features  
 
Where it is evident that structural or design features have contributed to the det erioration of coatings, they 
should be modified if practicable and economically justifiable and such modifications may include the 
following.  
 
a) improving drainage or run -off to avoid retention of water on horizontal surfaces;  
 
b) preventing discharge of  steam, water or industrial fumes on to coated surfaces;  
 
c) measures to prevent or reduce condensation on internal surfaces (see 4.6.4.3);  
 
d) sealing gaps, e.g. between wood frames and adjacent masonry;  
 
e) providing drip mouldings or canopies over external doors and windows if they are exposed to 
rainwater run -off; 
 
f) providing guard rails to prevent damage to painted walls in heavy traffic areas, e.g. corridors in 
factories and hospitals;  
 
g) enclosing plant and equipment to prevent splashing or s pillage.  
 
Where painted surfaces are subject to very heavy wear or other forms of attack, alternative materials should 
be used, e.g. ceramic tiles or plastics sheets or components.  
 
11.2.5  Atmospheric pollution  
 
Painted surfaces subjected to heavy soiling  and/or pollution from road traffic should be cleaned regularly 
(see 11.5.3) and might require more frequent painting.  
 
11.2.6  Building function  
 
The function of a building or the type of occupancy should be established in order to determine the rate of 
deterioration of coatings, the type systems used and the frequency of maintenance.  
 
NOTE  The function of a building might also affect its availability for maintenance treatment. For example, 
maintenance might be possible only outside normal working hours a nd then only for limited periods, and this 
can affect costs or impose constraints on the selection of coating systems. Similar considerations might 
apply when maintenance can be carried out only during shut -down periods.  
 
Building function and occupancy is  likely to change and consideration should be given to the effect on 
maintenance requirement since the last or initial treatment.  
 
11.2.7  Patch -painting  
 
Where there are marked differences in the condition of paintwork on different parts of a building, pat ch-
painting should be considered.  
 
NOTE  Patch -painting, as a form of interim treatment, is generally more applicable to situations where protection is the major factor, 
e.g. on steel structures, and might not be acceptable where appearance is important.  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 105  
Where the area to be treated is easily accessible, patch -painting should be carried out. However, if a 
significant amount of scaffolding is needed, thereby making the cost of access a high proportion of the 
overall treatment cost, it might be more economic al to recoat the whole structure.  
 
11.3 Selection of coating systems for maintenance  
 
11.3.1  General  
 
Where the coatings used previously have performed satisfactorily, materials of similar type should be used 
for maintenance.  
 
Where performance has not bee n satisfactory, the reasons for this should be established which may include 
one or more of the following:  
 
a) application to new wet substrates, e.g. plaster, concrete, brickwork and similar materials;  
 
b) inadequate or incorrect preparation of surfaces;  
 
c) low film thickness in protective coating systems;  
 
d) adverse conditions, e.g. of temperature or humidity, during application;  
 
e) unskilled application;  
 
f) use of poor quality materials;  
 
g) use of materials of unsuitable type.  
 
NOTE  The type of coating used might have proved unsuitable either because the original requirements 
were not correctly appraised or because of subsequent changes in the exposure conditions, conditions of 
service or functions.  
 
Where a) is the cause of unsatisfactory perfor mance, this does not necessarily imply a need to use a 
different type of material, provided drying out is complete and the surface is correctly prepared.  
 
However, where a permeable type of coating was used for initial treatment, functional requirements m ight 
indicate a change to a coating more resistant to washing or wear.  
 
Where faulty performance is attributable to b), c), d), e) or f), corrective action should be taken in respect of 
procedures or quality of material rather than a change in the type of coating.  
 
Where g) is the cause of unsatisfactory performance, the principles described in 4.6 should be followed in 
selecting alternative coating systems and reference should be made to 4.6.4 for coating systems with special 
conditions and requirements.  
 
11.3.2  Compatability of coatings  
 
Generally, no problems will be encountered in applying successive coatings of similar type. Difficulties might, 
however, be experienced with some combinations of existing and new coatings of dissimilar type. The 
manufactur er's advice should be sought if there are doubts as to compatibility of old and new coatings, but 
the following are typical of circumstances that might require consideration.  
 
a) Application of water -borne coatings. Adhesion of these coatings, e.g. water -borne paints, over 
solvent -borne coatings might be poor, especially in conditions of high humidity and to glossy surfaces, which 
have to be abraded (see 11.5.4).  
  
106  © KEBS 2018 — All rights reserved  b) Application of solvent -borne coatings over water -borne coatings. This does not usually present a 
problem if the existing coating is sound and firmly adhering, but a primer -sealer (5/3) might be required on 
highly pigmented or absorbent coatings.  
 
c) Application of specialist coatings, e.g. two -pack epoxy or  polyurethane types, over drying - oil/resin 
coatings. This might be possible if the existing coating is sound, hard and aged, but there is a risk that 
softening, cracking or lifting will occur. The manufacturer's advice should be sought in cases of doubt, and 
small -scale trials might be ne cessary.  
 
d) Application of drying -oil/resin coatings over zinc -rich primers. Advice should be sought when drying -
oil/resin coatings are to be used over zinc -rich primers.  
 
e) Application of all types of coatings over bituminous coatings (see 8.15 and 11.5 .9.2).  
 
Difficulty can sometimes be experienced in identifying existing coatings Q by type especially in older 
buildings although in most cases this is not ^ significant in relation to the selection of coatings for 
maintenance.  
 
Where identification is nec essary, either simple site tests, e.g. the reaction of the coating to solvents of 
various types, or in other cases, laboratory examination should be undertaken to provide the information.  
 
11.3.3  Components of maintenance coating systems  
 
If the existing c oating is generally in sound condition and materials of similar type and colour are to be used 
for repainting, either one undercoat and one coat of finish, or two coats of finish, as appropriate, will usually 
provide a satisfactory result. Allowance should  be made for bringing forward (see 11.5.7) localized areas 
from which the old paint has been removed.  
 
Additional coats might be required if a pronounced colour change is to be made, especially if the change is 
from a dark colour to white or a light colour . Additional coats might also be necessary with some bright or 
strong colours; reference should be made to manufacturer's literature for guidance.  
 
Exceptionally, e.g. on internal work in good condition and where the same or a similar colour is to be used,  
one coat of some types of finish might suffice, but manufacturer's recommendations hi this respect should be 
followed.  
 
Surfaces from which the old coating has been removed completely should receive a full system as described 
for new substrates in Clause 8. 
 
11.4 Organization of maintenance work  
 
Reference should be made to Clause 5 for general guidance on organization and Clause 9 for general 
guidance on conditions of application and procedures. The following factors which have particular relevance 
to mai ntenance work should also be taken into account:  
 
a) Restricted access, e.g. a requirement that the work be done only at night or weekends. This might 
impose constraints on the nature or standard of preparatory work or the types of coatings that can be use d. It 
is also likely to increase costs.  
 
b) It might be necessary to isolate the working area, e.g. by the erection of temporary screens or 
partitions, to limit interference with the normal functions of the building. Similar precautions might be required 
in order to create a satisfactory working environment, e.g. to exclude process fumes or dust from the working 
area during application of coatings.  
 
c) In some circumstances, e.g. in food factories, precautions might have to be taken to prevent 
contaminatio n of products by solvent vapours or other constituents of coatings. Isolation of the working area, 
as in b), might be sufficient, but there might also be constraints on the types of coatings that can be used. 
Specific requirements should be established and  the measures to be taken agreed between client and 
contractor.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 107 Reference should be made in specifications to these and any other special requirements or conditions which 
might affect the organization of maintenance work.  
 
11.5 Preparation of painted surfaces  
 
11.5.1  General  
 
The preparation of painted and similarly treated surfaces should involve one or more of the following 
processes:  
 
a) removal of coatings (see 11.5.2);  
 
b) cleaning (see 11.5.3);  
 
c) abrasion (see 11.5.4);  
 
d) priming (see 11.5.5);  
 
e) stopping and filling (see 11.5.6);  
 
f) bringing forward (see 11.5.7);  
 
g)  treatment of biological growths (see 11.5.8);  
 
h) treatment of stains and discoloration (see 11.5.9).  
 
NOTE  On the assumption that preparatory work will be carried out by skilled and experienced operatives, 
techniques and methods are not described in detail.  
 
For information on the preparation of old unpainted surfaces, e.g. exterior masonry and non -ferrous metal, 
reference should be made to the relevant substrate in Clause  8. 
 
11.5.2  Removal of coatings  
 
11.5.2.1  General  
 
Whether or not a coating is to be removed will depend upon its condition and its compatibility with the 
coating to be applied.  
 
If the existing coating is in sound condition and one of similar or compatible type is to be applied, removal is 
unnecessary. A significant difference in colour between the existing paint and that to be applied does not 
usually justify its removal.  
 
Complete or partial removal of coatings should be undertaken where there i s general poor adhesion, flaking, 
peeling, blistering, cracking, crazing and severe chalking or powdering of the coating. Rough (e.g. heavily 
brushmarked) or textured coatings, although generally sound, should be removed for maintenance purposes, 
where the ir smoothing or levelling would be impracticable or more costly than removal.  
 
Where the coating to be applied is not compatible with the existing one, e.g. if a specialist coating containing 
strong solvents is to be applied over a coating of conventional type, the coating should be removed. General 
guidance on the compatibility of coatings is given in 7.3.5, but the manufacturer's guidance should be sought 
in case of doubt.  
 
Where the general condition of a coating is obviously poor, it should be removed.  
 
NOTE   Frequently, however, and especially in older buildings, the extent to which removal is necessary 
might not become apparent until work has started; for example, what might have appeared to be isolated 
flaking might prove to be indicative of poor adhe sion overall.   
108  © KEBS 2018 — All rights reserved   
When there is doubt about the extent to which coatings should be removed, the specification should include 
a contingency allowance for the removal of coatings from a stated percentage of the areas affected and for 
the subsequent measurement of the area of the coatings actually removed.  
 
11.5.2.2   Removal by heating  
 
WARNING Removal of paint by heating can result in the emission of toxic fumes and should not be used for 
the removal of paints containing lead pigment.  
 
11.5.2.2.1   Burning off  
 
Burning off with a blowtorch is usually the quickest and most economical for some types of coating, such as 
conventional oil or alkyd paints. It is not effective on all coatings and a test should be carried out on a small 
area before proceeding.  
 
It should  not be used to remove highly flammable coatings, e.g. cellulose types, or in proximity to flammable 
materials.  
 
Burning off should not be used for removing coatings from woodwork that is to be recoated with a clear or 
semi -transparent coating system, beca use the wood might be scorched or discoloured. Burning off should 
not be used for carved or heavily moulded woodwork as it is generally impracticable.  
 
Plaster, cement rendering, asbestos -cement and similar substrates should not be burned off unless the 
coating is of sufficient thickness to soften without transmitting excessive heat to the surface, otherwise 
cracking or disintegration, which might become explosive, can occur. Even then, only a low flame should be 
used.  
 
Burning off should not be used for me tal, as heat is conducted away too rapidly for burning off with the 
normal type of blowtorch to be effective. Flame cleaning (see 8.3.4.2.3) can be used to remove most paint 
coatings from steelwork, but this is not usually the essential reason for its use.  
 
During burning off, all flammable materials, e.g. curtains and hangings, should be removed from the working 
area. Great care should be taken about burning off in situations where the flame might penetrate gaps and 
ignite accumulated rubbish such as old b irds' nests. Means of extinguishing fire should be readily available. 
Burning off should be completed well before operatives leave the work area. Burned off surfaces and 
surroundings should be carefully inspected before leaving the work area to ensure that  there are no signs of 
combustion (e.g. smouldering and high surface temperatures)  
 
11.5.2.2.2 Hot air  
 
Paint coatings can be softened by heat generated by passing a stream of air through an electrically operated 
heating element. Although the temperature o f the air (up to 600 °C) is lower than that of a gas blowtorch 
(approximately 1 900 °C), it is sufficient to soften and permit the removal of oil -paint coatings. Although the 
absence of a flame decreases the fire hazard and the risk of damage to the surfac e, great care should still 
be taken.  
 
11.5.2.3 Paint removers  
 
Paint removers should be used to remove coatings when the nature of  the substrate or other considerations 
precludes removal by heating as described in 11.5.2.2. There are two main types of pai nt remover: alkaline 
(or caustic) and organic solvent.  
 
Alkaline paint removers, based on caustic soda, potash or similar material, are low in cost, non - flammable 
and water -rinsable. They readily saponify drying -oil/resin coatings but are usually ineffect ive with other types. 
They attack aluminium and zinc, and their residues are difficult to remove especially from porous surfaces.  
 
Solvent -type paint removers can be based on flammable or non -flammable solvents. Solvent -type paint 
removers as specified in BS 3761 are based on dichloromethane and are non -flammable and water -rinsable 
and should be used for removing solvent -borne coatings. For other types of coatings including water -borne KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 109 paints and two -pack coatings, solvent -type paint removers of similar typ e, but not necessarily conforming to 
BS 3761, may be used.  
 
Paint removers should be applied liberally and left until the coating has softened sufficiently to enable it to be 
removed easily. Thick films can require several applications. When removal is complete, the surface should 
be cleaned in accordance with the manufacturer's instructions. With alkaline types,  
vinegar or acetic acid can be added to the rinsing water to neutralize residues.  
 
In using paint removers, lungs should be protected with a res pirator, skin contact should be avoided, and the 
eyes and hands should be protected. Solvent -borne types should be used in conditions of good ventilation 
(see also B.1.4, B.2 and B.3).  
 
Particular care should be taken with industrial or phenolic paint remo vers.  
 
11.5.2.4 Washing off  
 
Non-washable size distemper, once widely used for ceilings, might be encountered in older buildings. It is 
essential to remove it before repainting, and this should be done by soaking the material with water until it 
has softened and can be sponged, scrubbed or scraped off.  
 
Other water -borne coatings, including some water -borne paints, while not soluble in water might lose 
adhesion when thoroughly wetted to an extent that permits their removal (see also 11.5.2.7).  
 
11.5.2 .5 Scraping  
 
Coatings having poor adhesion, locally or generally, can often be removed by scraping, without recourse to 
burning off or the use of paint remover. When local areas of poorly adhering material are removed in this 
way, it should be ensured that  adhesion of the remainder is satisfactory and that the defective coating is 
removed back to a firm edge.  
 
11.5.2.6 Abrasion  
 
Abrasion includes hand or mechanical sanding, abrasive discs and pads and wire brushing and should be 
used for removing perished, heavily chalking or poorly adhering coatings. It might be the only practicable 
method of preparing external walls having an accumulation of coatings of miscellaneous type in poor 
condition. In such circumstances, complete removal of the residues of old coa tings back to a sound surface 
might be difficult and application of a primer -sealer (5/3), after thorough preparation, might be necessary 
(see 11.5.5).  
 
Precautions should be taken to prevent inhalation of dust and to protect eyes (see Annex B).  
 
11.5.2.7  Steam stripping  
 
Steam stripping equipment involves steam being generated and supplied to a perforated pad held against 
the surface from which a coating is to be removed. The equipment was designed originally for use in the 
removal of wallpaper but has bee n found to be of assistance in the removal of water -borne paints from 
interior walls and ceilings. Steam stripping should be used for large areas, as it can be more effective than 
the washing -off method referred to in 11.5.2.4.  
 
11.5.2.8  Abrasive blasting  
 
Abrasive blasting (see 8.3.4.2.1) can be used for the removal of heavy accumulations of old coatings from 
external wall surfaces, and consideration should be given to its use when warranted by the condition of the 
coatings and the extent of the areas. To avoid possible damage to the substrate, care should be taken in the 
selection of abrasives and air or water pressures, and the work should be carried out only by experienced 
contractors.  
  
110  © KEBS 2018 — All rights reserved  High-pressure water cleaning, referred to in 11.5.3, can also be an effective method of removing old coatings 
from external walls.  
 
11.5.3  Cleaning  
 
If coatings are generally in sound condition and of types not likely to be affected by wetting, superficial dirt 
should be removed by washing with a solution of sugar soap, ho usehold detergent, cleaning powder or mild 
soap. Strongly alkaline solutions, which can attack the coating or leave undesirable residues, should not be 
used. Proprietary cleaning materials should be used strictly in accordance with the manufacturer's 
instructions. With all types of cleaning solutions, final rinsing with clean water before the solution has dried is 
essential. After rinsing, surfaces should be dried off and time be allowed for absorbed or trapped moisture to 
dry out before coatings are applie d. 
 
Washing might not be advisable for water -borne coatings, including some water -borne paints, whose 
adhesion might be impaired by excessive wetting. Most good quality water -borne paints will, however, 
withstand sponging with a mild cleaning solution and even light scrubbing of soiled areas. If there is any 
doubt about the advisability of wetting the surface, cleaning should be limited to dry abrasion and dusting off.  
 
Washing with cleaning solutions might not remove contaminants such as oil, grease, silic ones and wax 
polish, which can impair the adhesion or prevent the drying of coatings. Contamination of this kind is likely to 
be encountered in industrial buildings, but it can also occur in other situations, especially around opening 
edges of doors or on skirtings adjacent to polished floors. Light contamination can be removed by wiping 
with a clean cloth and proprietary cleaner followed by washing with cleaning solution and rinsing with clean 
water. Proprietary emulsion cleaners or degreasing solutions sh ould be used for the removal of silicones or 
heavy deposits of oil or grease, as necessary.  
 
High-pressure water cleaning equipment can be used when soiling is heavy and the area to be cleaned is 
extensive. Equipment is available which delivers hot or cold  water or detergent solutions at pressures of 7.0 
MPa (1 000 lbf/in2) or higher.  
 
11.5.4  Abrasion (rubbing down)  
 
NOTE      Abrasive materials and methods are described in 9.2.3.  
 
Gloss coatings should be abraded to provide adhesion for the new coating, ca re being taken not to cut 
through to the substrate. Abrading assists cleaning and can be combined with washing by using waterproof 
abrasive paper. Lead -based paint surfaces should be wet -abraded (see B.1.2)  
 
Surfaces from which coatings have been removed b y burning off or with paint remover, should then be 
abraded.  
 
11.5.5  Priming  
 
Surfaces from which coatings have been removed should be primed depending upon the nature of the 
substrate and the type of coating to be applied. Reference should be made to the appropriate substrate in 
Clause 8 for guidance.  
 
As noted in 11.5.2.6, it can be difficult to remove perished, heavily chalking or poorly adhering coatings 
completely, especially from external walls. Preparation, usually by thorough scraping and brushing, should 
be followed by application of a primer -sealer (5/3) to bind any residual material and reduce the risk of 
subsequent flaking. It is emphasized that application of a primer -sealer is supplementary to thorough 
preparation; too much reliance should not be placed on the ability of these materials to penetrate multiple 
layers of old coatings. Penetration can be assisted by thinning, but the manufacturer's recommendations 
regarding this should be followed.  
 
Glazing rebates, exposed by the removal of defecti ve putties, should be primed before re -applying putty.  
 
If discoloration or staining of the existing paint has occurred (see 11.5.9), a sealer should be applied, as 
necessary.  
 
11.5.6  Stopping and filling  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 111  
The materials and methods employed in filling sho uld be selected in accordance with 7.4.4 and 9.2.4 
respectively.  
 
11.5.7  Bringing forward  
 
Bringing forward refers to the repair of localized areas, e.g. where defective paint has been removed and the 
substrate is exposed to provide a uniform surface before application of finishes. Treatment will depend upon 
the nature of the substrate and of the existing system but, typically, should include priming, stopping and 
filling and the application of further coats to restore the original film thickness.  
 
11.5.8  Treatment of biological growth  
 
11.5.8.1 General  
 
The information in this subclause is based upon that given in BRE Digest 370 [6] to which reference should 
be made for a more comprehensive treatment.  
 
11.5.8.2 External surfaces  
 
Lichens and mosses ar e often found on roofs and external walls especially in rural areas. Their appearance 
is often regarded as pleasing but, if the surfaces are to be painted, the growths have to be removed. Algae 
occur in most districts when water runs freely over a surface;  they cause unsightly green or black stains and 
have to be removed before painting. Moulds and algal growths resembling dirt deposits can occur outdoors 
on paints and wood stains; in the early stages they can be washed off, but moulds can penetrate and 
damage the existing coatings and affect the new one.  
 
Where growths are present on surfaces that are to be painted, preparatory treatment should include 
application of a surface biocide.  
 
NOTE  Active chemicals used in surface biocides are subject to scrutiny for safety in use under the Control of Pesticides Regulations 
1986 (as amended) [11] and require that only products with an HSE registration number be used. This regulation is being absor bed into 
the Biocidal Products Regulations 2001 [21], however it is a n offence to use any pesticidal product without approval under the 
appropriate Regulations.  
 
The efficiency of surface biocides will vary according to circumstances, for example sodium hypochlorite is 
readily available and is effective with a wide range of  growths but has no residual activity.  
 
When using surface biocides, the manufacturer's instructions should be followed regarding the use of 
protective clothing (e.g. goggles, gloves, overalls).  
 
NOTE   Professional  operators  will  need  to  take  into  a ccount  procedures  required  under  the  Control  of  Substances 
Hazardous to Health Regulations 2002 (COSHH) [5] and see B.2.  
 
Surface biocides take a few days to become effective and, in wet weather, can be washed out before they 
have had tune to act. T hey should preferably be applied during a dry spell. To hasten the biocide action, 
thick surface growths should be partly removed or torn with a stiff but not wire brush before brushing the 
wash well in. The wash, repeated if necessary, kills the growth, b ut the dead organism takes some time to 
disappear. The dead matter should be removed by scraping and brushing, and this is often more effective 
when the growth is dry; however, it is important that asbestos -cement be not scraped or brushed except 
when wet.  All dust and debris should be carefully collected, sealed in plastic bags and disposed of in a safe 
manner. After removal of the dead growth, a further application of surface biocide (with types having a 
residual effect) can be used to delay re -establishm ent of the growth.  
 
Heavy growths should preferably be removed from external walls by abrasive blasting (see 11.5.2.8)  or high -
pressure water cleaning (see 11.5.3) when circumstances permit or warrant their use and should 
subsequently be treated with a sur face biocide.  
 
11.5.8.3 Internal surfaces  
  
112  © KEBS 2018 — All rights reserved  Mould (mildew) is the form of biological growth most likely to affect internal surfaces. The conditions and 
exposure conditions favourable to its development and measures to prevent or control it are described in 
4.6.4.4. Preparatory treatment of painted or papered surfaces will depend upon the type of decoration and 
the extent to which it is affected.  
 
Wallcoverings should always be stripped if mould is evident on or beneath them. Paint should be removed if 
it is severely affected and the growth is deep -seated. In disposing of stripped paper or paint,  care  should  
be  taken  to  avoid  contaminating  unaffected  surfaces.  After  removal  of wallcoverings or  paints,  the  
surface  should  be  treated  with  a  s urface  biocide  and  kept  under observation for a week or so, a further 
wash being applied if growth is renewed. When growth has ceased and the surface is dry, it can be 
redecorated.  
 
Where infection is slight and the coating is of a type which will with stand application of a surface biocide, it 
might be sufficient to clean down without removing the coating and then to apply the wash, allow to dry and 
repaint.  
 
11.5.9  Stains and discoloration  
 
11.5.9.1 General  
 
Staining or discoloration evident in the ex isting coating might be transmitted to the new one unless 
preventive measures are taken. Constituents of the existing coating or the substrate might also cause 
discoloration of the new coating although it might not have been apparent previously. Some types  of mould 
can cause discoloration but the mould itself might not be visible. Diagnosis of the causes of staining or 
discoloration and recommendations for remedial treatment can require expert investigation but some typical 
examples are described in 11.5.9. 2 to 11.5.9.6. Specialist stain resistant paints are available.  
 
11.5.9.2 Bitumen staining (bleeding)  
 
Where bitumen surfaces need to be overpainted, they should be treated in accordance with 8.15.  
 
11.5.9.3 Knot staining  
 
Discoloration of paint over knots  and resinous areas can be indicative of incorrect or inadequate treatment 
during initial painting and might be transmitted to coatings applied during maintenance painting. If the 
existing coating is generally in good condition, i.e. does not need to be re moved, further staining should be 
minimized by applying fresh knotting or specialist knot treatment.  
 
11.5.9.4 Tobacco tar staining  
 
Tobacco tar staining is caused by the deposition of the tarry matter in tobacco smoke. It often results in 
severe yellowing  or browning of painted surfaces and might cause staining and retarded drying of 
subsequent coats. To remove the deposit, the coat should be scrubbed with a solution of household 
detergent or cleaning powder. However, to reduce the risk of the new coating being affected, a coat of 
aluminium primer (3/4), primer -sealer (5/3) or a proprietary stain blocker can be applied.  
 
11.5.9.5 Stains from wallpaper  
 
Treatment might be required to prevent staining of water -borne paints applied over some types of wallpaper  
although, if there is a risk of this occurring, the wallpaper should be removed (see 8.12.1.2).  
 
11.5.9.6  Pattern staining  
 
Pattern staining is a thermal effect, differing rates of heat flow through a composite structure causing 
variations in the amount of dust deposited upon a surface.  
 
NOTE  A typical example is often seen in ceilings where the presence of joists or beams is indicated by lighter or darker areas. 
Mortar joints in blockwork and fixings in claddings and linings can produace a similar effect . 
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 113 Paint treatment cannot significantly affect the rate of heat flow and the consequent deposition of dust but, 
where pattern staining rapidly develops, paints, which resist soiling and can withstand frequent washing, e.g. 
gloss and mid -sheen types, should  be used.  
 
11.6 Application  
 
The general considerations regarding application methods and techniques as described in Clause 9 should 
be followed. Spray equipment should not be used in occupied buildings in circumstances where spray mist 
would create a nuisance (see 9,3.6.1) and petrol or diesel engine compressors should not be used in 
situations where noise and exhaust fumes should be avoided.  
 
 
   
114  © KEBS 2018 — All rights reserved  Annex A  
(informative)  
Types of coatings  
 
A.1 General  
 
For the purposes of this code, paints and similar coatings are grouped in three categories as follows:  
 
a) conventional coatings (see A.2);  
 
b) specialist coatings (see A. 3);  
 
c) factory -applied coatings (see A.4). Metallic coatings are referred to in 8.4.  
 
A.2 Conventional coatings  
 
Conventional coating s represent the greater proportion of the coatings in general use in the painting of 
buildings and are based mainly on drying -oil or water -borne binders. They are listed and described in Tables 
3 to 10, generally according to their functions within the coa ting system.  
 
Conventional coatings based on binders of the types referred to in Tables 3 to 10 can be modified to impart 
specific properties, e.g. of mould -resistance or fire protection (see 4.6.4).  
 
A.3  Specialist coatings  
 
Specialist coatings have prop erties, e.g. of chemical resistance, hardness or other characteristics, not 
possessed by materials of conventional type (see 4.6.4). They might require special techniques or conditions 
of application or necessitate high standards of surface preparation and  might not be readily available from 
normal sources of supply. Often, the complete system is of specialist type and might not be suitable for use 
over primers or existing coatings of conventional type. For these reasons specialist coatings have limited 
usage in the painting of buildings.  
 
Table 11 summarizes the characteristics of the principal types of specialist coating. Within the generic 
categories, there can be considerable variation in the formulation and, in consequence, the characteristics of 
indivi dual materials.  
 
Reference to manufacturer's recommendations is advised when there appears to be a requirement for the 
use of specialist coatings. BS EN ISO 12944 and BS 5493 give detailed recommendations regarding 
specialist coatings for the protection of  iron and steel structures.  
 
Table 11 lists specialist coatings that can give extra resistance and/or durability. These coatings can 
themselves be  further  modified to  provide specific properties such  as  mould  resistance or  fire protection.  
 
A.4  Factory-applied coatings  
 
These range from stoving or air -drying paints, applied to wood and metal components by spraying or 
dipping,  to  coil  coatings  mechanically applied  to  coiled  flat  sheet  for  subsequent  forming  and 
fabrication. Coatings of ty pes unsuitable for site application might be employed; correctly chosen and 
applied, they can be tougher, harder and more durable than most site -applied coatings. These coatings can 
all be overpainted for aesthetic or maintenance purposes, by the correct c hoice of primer and top coat. The 
most common factory applied coating is PVC plastisol but more variation in coating types now exists (see 
8.13.4).  
 
For light gauge steel, BS 5493 gives guidance in choice of coatings, although there have been 
improvements in and additions to the types there described. Organic coatings for aluminium extrusions (e.g. 
windows) are defined in BS 4842, and the expected performance of a variety of coatings on metal and other 
claddings is tabulated in BS 5427 -1. No such guidance i s available for complete factory -applied systems on 
timber, but they can give better durability than the conventional site -applied coatings at no greater cost.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 115 Components for interior use are sometimes coated by processes suitable for the dry conditions o f a 
completed building, but inadequate for exposure to weather or condensation during erection. To avoid 
premature failure, a higher grade coating might have to be specified. Likewise, the life indicated for various 
categories could be extended by addition al coats or increased thickness.  
 
   
116  © KEBS 2018 — All rights reserved  Annex B  
(normative)  
 
Health and safety  
 
NOTE  The list of health and safety hazards in Annex A does not purport to be exhaustive.  
 
B.1 Hazards  
 
B.1.1  General  
 
The materials used for painting buildings are made from a wide  range of chemical substances, some of 
which are toxic. However, if suitable precautions are taken, these materials can be used without risks to 
health.  
 
NOTE The Control of Substances Hazardous to Health Regulations 2002 (COSHH) [9] require employers to 
assess the risks which might arise from hazardous substances at work and then to determine the measures 
needed to prevent or adequately control exposure to them. For further information see HSE publication HSG 
97, A step by step guide to COSHH assessment [ 22]. 
 
The risk of exposure depends on the nature of the materials used, the conditions of use and the way in 
which preparation is implemented.  
 
It might be possible to eliminate a hazardous substance either by changing the process or substituting a safe 
or safer substance. Where this is not reasonably practicable, exposure should be controlled by, for example, 
enclosure, the use of ventilation equipment, general ventilation, safe systems of work and handling 
procedures. Personal protective equipment should only be used where other measures cannot adequately 
control exposure.  
 
In addition to the manufacturer's recommendations, precautions to be taken by those engaged in the painting 
of buildings should include the following.  
 
a) The least hazardous product an d system of working should be used.  
 
b) Overalls should be worn while working but should be removed before eating and before leaving 
work. They should be laundered at frequent intervals. Gloves, goggles and a suitable respiratory protection 
should also be worn when a hazard exists.  
 
c) Reasonable measures should be taken to keep painters' materials off the skin, and hands should be 
washed before eating or drinking. Silicone -free barrier creams should also be used. Smoking while working 
should be discouraged  since this can cause paint to be transferred to the mouth.  
 
d) It is essential that paints, solvents and other painters' materials are not placed in containers normally 
used to hold food or drink, and they should be kept out of reach of children and anima ls. Residues should be 
disposed of safely.  
 
e) If paint, solvent or other material is accidentally swallowed, medical attention should be sought 
immediately.  
 
f) Adequate ventilation, either mechanical or natural, is essential.  
 
B.1.2  Lead paints  
 
The use of lead paints has declined in recent years but surfaces in older buildings might have been painted 
with lead paints. If this is the case, the dust created by dry abrasion is a hazard; and so wet abrasion (see 
9.2.3) should be undertaken as it is safer and  also more effective.  
 
NOTE  Because of the possible toxic hazard involved, the use of lead paints and the preparation of lead -painted surfaces are subject 
to legislation Control of Lead at Work Regulations [8]. For further information on lead and its expos ure levels at work see HSE 
publications LI 32, Control of lead at work [23] and EHW/2005, Workplace exposure limits [24].  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 117  
Lead paints should not be used on surfaces which might be licked or chewed by children or animals.  
 
B.1.3  Fungicidal washes and coatings  
 
Some coatings and preparatory washes might contain or be based on materials intended to inhibit moulds or 
other biological growths (see 11.5.8). While the use of inhibitors having atoxic effect on humans or animals is 
unlikely, the manufacturer's  recommendations regarding their application and also their use on surfaces in 
contact with foodstuffs should be strictly observed.  
 
B.1.4   Vapours, fumes and dusts  
 
Inhalation of solvent vapours in high concentrations can cause narcosis and can affect the  respiratory or 
digestive systems. Irritation of the eyes, nose and throat can also occur. These effects should be prevented 
by ensuring that there is sufficient ventilation of the compartment being painted to control solvent vapour 
concentrations.  
 
NOTE 1  Attention is drawn to the Control of Substances Hazardous to Health Regulations 2002 [9]. Occupational exposure limits, 
which should be used for the purposes of these Regulations, are reproduced in HSE Guidance Note EHW/2005 [24].  
 
If solvents, notably wh ite spirit, are used for cleaning, only the minimum amount necessary should be 
employed. Skin contact with the solvent should be avoided (by wearing suitable protective gloves) and, as 
with painting, the work area should be well ventilated to prevent the b uild up of solvent vapours. Sufficient 
time should be allowed for solvent to evaporate before work proceeds.  
 
Chlorinated solvents such as dichloromethane, that are used in some paint removers (see 11.5.2.3), are 
much more volatile than ordinary paint solv ents, and the vapours, if allowed to accumulate, are powerful  
anaesthetizing agents.  Also,  if  the  vapours  come  into  contact  with  flames  or  red -hot surfaces, they 
might decompose to form toxic substances. Accordingly, when using paint removers c ontaining chlorinated 
solvents, it is essential that adequate ventilation is provided and that sources of ignition, including lighted 
cigarettes and pipes, are excluded from the working area.  
 
Certain types of paint present particular toxic problems when a pplied by spraying. These include, for 
example, two -pack epoxy coatings, which can be potent skin and eye irritants, and two -pack polyurethane 
paints which contain isocyanates and present serious health hazards through inhalation of paint mists. 
Precaution ary measures should be taken to prevent exposure to mist and vapour arising from their use, as 
both of these classes of paint can cause sensitization. When this is not reasonably practicable, a very high 
standard of control measures should be taken.  
 
There  should be sufficient flow of air through compartments being painted in order to control solvent vapour 
concentrations adequately. Under some circumstances this may be achieved by natural ventilation, i.e. by 
means of windows or doors that open directly to  outside the building. Where natural ventilation on its own is 
not always reliable and might not always provide a sufficient flow of fresh air through the space or where 
natural ventilation is not possible (e.g. in underground and windowless compartments, pits, tank interiors, 
operating theatres etc.), a mechanical means of ventilation should be provided.  
 
Factors such as the wind conditions outside the building, the volatility of the solvents involved, the rate of 
application of the paint and the surface a rea to be coated should be taken into account when deciding upon 
the method and extent of ventilation. In difficult or unusual circumstances, professional advice on ventilation 
should be sought.  
 
Where vapours are created, for example in the spray applicat ion of two -pack polyurethane paints and epoxy 
surface coatings, or where surface preparation work creates dust and fumes, this should be regarded as 
potentially hazardous to health. Where it is not possible to control exposure to vapours, dust and fumes 
adequately by other means, then suitable respiratory protective equipment should be worn. It is also 
recommended that accumulations of dust on floors, ledges etc. should be removed with an industrial vacuum 
cleaner rather than by sweeping.  
  
118  © KEBS 2018 — All rights reserved  NOTE 2  Respirato ry protective equipment can be regarded as suitable if it is a type -approved by the Health and Safety Executive 
(HSE) or conforms to a standard approved by the HSE. For further information on respiratory protective devices, see BS  4275  and  
HSE  Guidance   Note  EH/16,  Isocyanates:  Health  hazards  and  precautionary  measures  [25].  For  further information on protection 
against dust, see HSE Guidance Note EH/44, Dust: General principles of protection [26].  
 
Special precautions should be taken in work involving building materials containing asbestos.  
 
NOTE 3  Attention is drawn to the Control of Asbestos at Work Regulations 2002 [27], which requires that any asbestos - containing 
material is assessed for the likelihood of release of asbestos fibres if disturbed, and that a safe working environment is maintained with 
respect to all asbestos materials identified. The supply and application of paints and varnishes containing asbestos are not permitted 
under the Asbestos (Prohibitions) Regulations 1992 [28]  made under the Health and Safety at Work etc. Act 1974 [29], In case of doubt 
or for detailed guidance, reference can be made to the Health and Safety Executive and to HSE Guidance Notes HSG248, Asbestos : 
The analysts' guide for sampling, analysis and cle arance procedures [30] and HSE Guidance Notes EH40/2005, Workplace exposure 
limits [24] (see also K.3.2 and K.3.3).  
 
B.2 Injury to eyes and skin  
 
Materials such as paint removers, alkaline cleaning solutions and some of the inhibitive washes referred to in  
11.5.8 can cause serious injury if they enter the eyes. They might also have a harmful or irritant effect on the 
skin. When these and materials of a similar type are used, measures should be taken to prevent them from 
coming into contact with the skin. Wh ere the circumstances or conditions of working are such that heavy 
contamination of the hands cannot be avoided, impervious industrial gloves should be worn.  
 
Eye protection should be worn, especially when working overhead. Eye protection should be used du ring 
paint spraying and during surface preparation work such as chipping, scraping and mechanical sanding, as 
necessary.  
 
NOTE  Attention is drawn to Personal Protective Equipment at Work Regulations 1992 [31], which cover all 
equipment designed to be worn or held to protect against a hazard where risk cannot otherwise be 
adequately controlled. See also the Control of Substances Hazardous to Health Regulations 2002 [9].  
 
Hands and exposed areas of skin should be treated with silicone -free barrier cream befor e work starts, and 
should afterwards be cleaned with an approved hand cleaner. Hands should not be cleaned with paint 
solvents or thinners as this might result in skin complaints or the absorption of materials through the skin. 
Over -vigorous scrubbing or t he use of harsh cleaning powders or soaps should be avoided as it might also 
cause skin complaints.  
 
Impervious industrial gloves should be used if heavy hand contamination is likely.  
 
B.3 Fire and explosion  
 
Many of the materials used by painters are flam mable or will support combustion, so that suitable 
precautions should be taken in their storage, handling and use.  
 
NOTE 1  Highly flammable liquids (paint solvents such as toluene or xylene) are the subject of legislation and there are statutory 
requiremen ts with regard to their labelling, storage and use. Attention is drawn to the Highly Flammable Liquids and Liquefied Petroleu m 
Gases Regulations 1972 [32] apply to the storage and use of certain flammable liquids.  
 
Precautions should be taken to ensure tha t vapours of highly flammable solvents do not accumulate in a 
space or part of a space, which is being painted, as a potentially explosive mixture with air could eventually 
be reached. The vapour concentrations required to produce such a mixture (i.e. the lower explosive limit or 
LEL) are about 1% (v/v) in air and ventilation should be provided to ensure that 0.1% solvent vapour in air is 
not exceeded which gives a ten -fold safety margin.  
 
NOTE 2  Attention is drawn to HSE Guidance Notes L101, Safe work in c onfined spaces [33] and HSG178, The spraying of flammable 
liquids [34].  
 
It should be remembered, however, that there can be circumstances where breathing zone concentrations 
might be low but where pockets of high vapour concentrations nevertheless build u p quickly due to poor art 
distribution, for example in pits and similar confined spaces. It is thus important to ensure that there is good 
air distribution throughout the whole space and to recognize that this might require the provision of additional 
mean s of mechanical ventilation or dispersion to deal with such areas in which there would otherwise be 
httle or no air movement.  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 119  
Sources of ignition such as lighted cigarettes, matches, blow lamps, elements of electric fires, unprotected 
light bulbs, electri c motors which are not flameproof, etc. should be eliminated from any area where a 
flammable concentration of vapour might be present or arise.  
 
Rags soaked with paint can ignite spontaneously if they are tightly compressed in, for example, bins or in the 
pockets of overalls. They should be spread out in the open air outside the building to dry off, or placed in a 
metal bin with a close -fitting lid.  
 
NOTE 3  For further information, reference can be made to the advice given in the HSE publication HSG168, Fir e safety in construction 
work [13].  
 
B.4 Noise  
 
Precautions should be taken against exposure to noise levels, as prolonged exposure to a high noise level, 
e.g. from compressors and mechanical tools, can damage the hearing of operatives and others nearby.  
 
NOTE      Information  on  noise  levels  and  the  corresponding  maximum  exposure  times  is  given  in  
the  Noise  at  Work  
Regulations 1989 [35]. Further information can be found in the HSE publication L108, Reducing noise at 
work [36] (see also BS  
5228).  
 
B.5 Spillages  
 
Spillages of paint should be cleaned up as soon as they occur, with an inert absorbent material. The use of 
rags and sawdust should be discouraged. If used they should be disposed of safely.  
The area should be well ventilated to remove solvent fumes, and sources of ignition should be eliminated.  
 
B.6 Waste disposal  
 
Care should be exercised when disposing of waste, in particular if there could be heavy metal, e.g. lead, 
contamination of the waste.  
 
NOTE   Attention is drawn to Haza rdous Waste (England and Wales} Regulations 2005 [37] which set out the regime for the control 
and tracking of the movement of hazardous waste for the purpose of implementing the Hazardous Waste Directive (91/689/EC) [38 ]. 
 
   
120  © KEBS 2018 — All rights reserved  Annex C  
(informative)  
 
Wood  
 
 
C.1 Design considerations  
 
Timbers can be broadly divided into softwoods and hardwoods, and a range of species from both classes is 
employed in construction. Softwood timbers, derived from coniferous trees and which include species such 
as pine, spruce and  fir, account for the greater volume of timber used. They are relatively soft, easy to work 
and finish, though some species can present specific coating problems. Hardwood timbers derived from 
broad -leaved, deciduous trees are used in the UK selectively in  smaller volume. They are in general heavy, 
hard and close grained, and include many of the highly figured and highly coloured timbers valued for 
internal work. Many tropical hardwoods and some temperate species such as oak and chestnut also possess 
advant ages in terms of dimensional stability, moisture impermeability and decay resistance. The structure 
and properties of wood can have an important influence on the specification of the coating system, and on its 
subsequent performance in service.  
 
Coating of  wood might be required for purposes of decoration and protection. The decorative effect often 
derives from the colour and sheen of a paint coating, but wood is also one of the few substrates for which 
there is a demand for transparent coatings that presen t and enhance the visual appeal of the substrate. 
Protective purposes include the following.  
 
a) Sealing. Untreated wood surfaces absorb liquids, are subject to soiling and chemical staining, and 
are unhygienic and difficult to clean.  
 
b) Mechanical damage . Resistance to scratching and abrasion is an important requirement for flooring 
and some other internal applications.  
 
c) Stabilization. Surface coatings have a major effect on the rate of exchange of water vapour between 
wood and the surrounding atmosphe re, and hence can be an effective means of controlling the swelling and 
shrinking of the wood.  
 
e) Weather protection. Wood surfaces exposed to the weather without surface protection are subject to 
discoloration,  
 
f) defibration  
 
g) and greying.  
 
h) Preservation  and   protection.  Surface  coatings  cannot   generally  be   classed  as   wood 
preservatives as they are not toxic to wood destroying organisms and do not penetrate sufficiently deeply. 
Moreover in some circumstances paint can trap water in th e wood and increase any risk of decay. 
Nevertheless an intact paint film on all surfaces will prevent the wood becoming wet enough to support 
fungal growth, and will prevent the surface being colonized by moulds and other fungal spores. In this 
restricted sense paint contributes to the preservation of the wood surface.  
 
i) Flame retardance. Coatings can be applied to wood and wood -based panel products to raise the 
resistance to spread of flame.  
 
C.2 Characteristics  
 
C.2.1  Structure  
 
The properties encountered with wood are directly related to the origins of the raw material, namely the 
structure and functions of a tree. Wood is a cellular material in which most of the cells are aligned vertically in 
the tree, giving wood its characteristic grain. Ot her cells lie in horizontal bands (rays) running outwards in the 
tree. KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 121  
Moisture uptake in wood arises from the natural liquid pathways found in the growing tree and will occur in 
softwoods and hardwoods.  
 
C.2.2   Heartwood and sapwood  
 
The trunk of a young  tree consists entirely of sapwood, which not only provides mechanical support but also 
sap conduction processes essential to the life of the tree. As the tree ages, a core of heartwood develops 
which plays no part in fluid conduction and which gradually b ecomes impregnated with a wide range of 
resins, gums, tannins and other chemicals. Heartwood is often distinguished from sapwood by its deeper 
reddish -brown colour, and in most wood species possesses greater resistance to water uptake and a degree 
of natur al decay resistance. In general, the sapwood of timber is moisture permeable and susceptible to 
fungal decay, and its effective protection poses a greater challenge when used in applications where it is at 
risk of wetting.  
 
C.2.3  Moisture content  
 
Green ti mber contains both free water in the cell cavities and water absorbed by the cell walls. Reducing the 
moisture content to a mass fraction of about 25% to 30% of the oven -dry mass removes free water from the 
cell cavities, but the fibres remain saturated an d the wood is fully swollen; it shrinks progressively as more 
moisture is removed. Shrinkage is greatest across the grain and is reversible; changes in moisture content 
through exposure to ram or fluctuations in relative humidity cause alternate swelling a nd shrinkage.  
 
C.2.4  Permeability and penetration of liquids  
 
The permeable nature of wood affects not only moisture movement but also the ease of impregnation by 
preservatives and the behaviour of paint.  
 
In general, penetration is deeper and more rapid t hrough end grain than through lateral surfaces, and is also 
deeper and more rapid through sapwood than through heartwood. There are also differences in permeability 
between early and late growth areas causing differential swelling which imposes stresses on  surface 
coatings.  
 
C.2.5  Extractives  
 
Extractives are present as minor non -structural constituents of the cell -cavities and cell walls, and differ 
greatly in quantity and type in different wood species. In most species, the extractive content averages les s 
than a mass fraction of 5%, but in some tropical hardwoods, and in the knots of many softwoods, it can 
amount to a mass fraction of 30% or more. The chemical nature of the extractives in both hardwoods and 
softwoods is very variable.  
 
One of the most com monly encountered extractive problems is associated with knots in resin -rich softwoods 
such as Scots pine (European redwood) and British Columbian pine (Douglas fir). These resins basically 
consist of a blend of resin acids or rosin in turpentine, together  with small amounts of tannins, which are 
water -soluble and possess the property of darkening on exposure to light. The resin blend gives rise to two 
kinds of problems. In hot summer weather they are mobilized and exude to the wood -paint interface where 
they cause blistering of the paint. This problem is most severe when dark coloured paint has been used, and 
can also be aggravated by retained solvent from preservative treatment. The tannin extractives can 
additionally migrate into the paint to produce a br own discoloration in the area of paint over the knot, which is 
particularly noticeable on white and pastel shades, and especially on water -borne coatings. For such timbers 
coated with wood stains, the resin can penetrate through the film without disrupting  it or causing blisters.  
 
C.2.6  External influences — Moisture  
 
As a result of increased attention to heat conservation, internal condensation has assumed considerable 
importance as a source of moisture. The absence of flues, blocking of unused flues and airbricks, draught -
proofing and similar measures have greatly red uced internal ventilation rates, especially in domestic 
buildings, In consequence, the water vapour produced by normal domestic activities is unable to escape  
122  © KEBS 2018 — All rights reserved  readily and can migrate to colder rooms and condense on single -glazed windows, eventually penetra ting 
open joints, defective putties and other discontinuities in the paint film. This is a frequent cause of timber 
decay and paint failure on wooden window frames and sills. Wet rot in timber cladding or failure of the 
external paint can also be caused by  condensation within the wall cavity.  
 
Coating permeability has important implications on timber windows. These are usually subject to a higher 
temperature and relative humidity on the inside compared with the outside, and a consequent vapour 
pressure diff erential favouring the transport of warm moist air outwards through the timber frame sections. 
One of the functions of the interior paint is to provide a vapour barrier, and it is essential therefore that it 
possesses a relatively low permeability. Circums tances in which the inside coating is more moisture 
permeable than that outside, as for example through the use of a permeable water -borne paint inside and a 
solvent -borne alkyd outside, need to be avoided. This arrangement can result in interstitial conde nsation 
within the frame section and severe blistering of the exterior coating during cold weather.  
 
C.2.7   Preservative treatments  
 
Preservation of wood components such as exterior softwood joinery and cladding is desirable and is 
normally carried out in the factory. The main types of preservative used are organic solvent solutions of 
fungicides or water -borne micro emulsions applied by double -vacuum treatment or immersion. For cladding 
and outdoor applications, vacuum -pressure treatment with water -borne s alts or fungicides are also 
employed.  
 
C.2.8  Knot treatment  
 
Knotting is rarely effective in preventing physical disruption of paint films by heavy exudation of resin. This is 
more likely to occur externally over knots in surfaces exposed to strong sunligh t, which liquefies the resin 
and makes it more active. The use of light -coloured paints reduces solar heat gain and can therefore reduce 
resin exudation although it is unlikely to prevent it completely; also, the resin will be more obvious on a light -
colou red surface. An alternative is the use of an exterior wood stain (see 8.1.8.3).  
 
The widespread adoption of water -borne paints has given rise to significant problems of staining over knots 
due to extraction of light -sensitive tannins contained in the knots  into the coating (see C.2.5). Conventional 
knotting is relatively ineffective in preventing tannin staining; more successful results have been achieved 
through the use of stain -blocking primers containing reactive pigments.  
 
C.2.9  Coating systems for inte rior use  
 
C.2.9.1  Paint systems  
 
C.2.9.1.1  Water -borne paints  
 
Water -borne latex paints have long been accepted in wall painting but their adoption for internal woodwork 
has been hindered by their inferior flow and initial gloss properties compared with the traditional solvent -
borne alkyd. They have significant application advantages however, in particular low odour and rapid rate of 
drying which can permit the complete system to be applied in the working day.  
 
C.2.9.1.2  Transparent and semi -transparent finishes  
 
The provision of a clear seal or varnish finish to interior wood is a relatively straightforward operation and a 
wide variety of coating systems is available for this purpose. The traditional solvent -borne oil and alkyd resin 
still find applicati on, though there are moves to reduce solvent -content and for example to use de -aromatized 
white spirit. The wood colour can be equalized or altered by the application of a dye or stain before sealing, 
or this might be achieved by the use of an interior woo d stain. A full range of gloss levels is achievable, and 
where necessary coatings with good resistance to mechanical damage or staining can be obtained. Water -
borne varnishes have advanced considerably during recent years and in appearance and wear resista nce 
properties are now almost equivalent to the established solvent -borne types.  
 
C.2.10  Coating systems for exterior use  
 
C.2.10.1   General  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 123 Although decorative effect  is  important  for  exterior  wood  coatings, the  function that  is  of  vital 
importance is the protection of the wood substrate against deterioration by weathering agencies, principally 
sunlight and water, and biological attack. Exterior wood is moreover a very challenging substrate, in that any 
adventitious entry of water can lead  to dimensional movement in the substrate, biological deterioration, and 
adverse affects on coating adhesion.  
 
Much dissatisfaction with the performance of exterior wood coatings over the years has been caused by the 
use of unsuitable general -purpose alkyd -based paints that lacked sufficient flexibility to cope with the 
demands of an unstable wood substrate. In order to aid the selection of suitable coatings, considerable effort 
has been devoted to the development of performance standards. BS EN 927 -1 speci fies a system for the 
classification of coating materials and coating systems for exterior wood surfaces by  categories of  end  use, 
appearance and  exposure conditions. DD ENV 927 -2 is  a performance specification, based on a natural 
exposure test as giv en in BS EN 927 -3. The natural exposure test has also been incorporated in a British 
Standard for undercoat and gloss paints, BS7664. BS 7956 is a performance standard covering the 
performance evaluation of all classes of wood primers, namely solvent -borne , water -borne, aluminium and 
stain basecoats. It is advised that the standards of performance set in these standards are regarded as a 
minimum requirement for wood  
coatings.  
 
C.2.10.2  Exterior wood stains  
 
C.2.10.2.1  General  
 
Whereas the task of protecti ng and enhancing natural wood indoors is a relatively straightforward matter, the 
task of preserving the natural appearance of the wood outdoors is beset with difficulties. Clear and semi -
transparent coatings lack the opaque protective pigments that are pr esent in paints, and are in consequence 
less durable than opaque coatings so that maintenance intervals are shorter and overall costs higher. 
Crucially any breakdown of the coating exposes wood to weathering and biological attack, and often 
consequent disc oloration cannot be masked by fresh application of the natural finish.  
 
C.2.10.2.2  Solvent -borne exterior wood stains  
 
Solvent -borne exterior wood stains are generally based on alkyd resins dissolved in white spirit. They can be 
grouped into two broad classes, low -build and medium -build. The low -build products are typically of low 
viscosity and the most penetrative type of wood stain. They deposit relatively thin films on the surface, 
possibly only 10 um to 15 urn for a three -coat application, so the na tural features of the wood are least 
obscured. Low -build stains weather by erosion rather than by flaking, and require a minimum of preparation 
prior to recoatmg. On the other hand in exposed situations, erosion is relatively rapid and maintenance 
interval s of about three years might be appropriate. Low -build stains have high moisture permeabilities, and 
exert relatively poor control on wood moisture content. There is a risk of significant dimensional movement 
and possibly surface splitting, especially as e rosion of the stain occurs during weathering.  
 
Low-build stains possess additional technical advantages. They are very tolerant of imperfections such as 
splits, knots and nail holes, and their good penetrative properties enables them to cope well with weat her-
degraded surfaces. Resin in knots can exude through the very thin surface film without causing disruption; 
when the resin acids have hardened the residue can be removed from the surface by light scraping.  
 
Medium -build stains contain a higher proportio n of resin and apply a higher film thickness of the order of 30 
(am to 40 urn for the complete system. They are less permeable than low -build types and exert better 
moisture control on the timber, thus reducing the degree of dimensional movement and risk o f surface 
splitting. They are more resistant to erosion, and require less frequent maintenance than the low -build types.  
 
C.2.10.2.3   Water -borne wood stains  
 
Water -borne acrylic and alkyd resins or alkyd -acrylic blends are increasingly being used in the formulation of 
medium -build wood stains and can give good durability. However, they penetrate less deeply into wood and 
may therefore be used over a solvent -borne priming stain.  
  
124  © KEBS 2018 — All rights reserved  C.3 Wood -based panels products  
 
C.3.1  Characteristics  
 
C.3.1.1  Plywood  
 
Plywood has many of the general characteristics of solid timber, including susceptibility to the effects of 
moisture although the method of construction gives it greater dimensional stability with changes in moisture 
content.  
 
Checking varies in severity a ccording to the species of timber used for the outer veneer. It is less severe, for 
example, with African mahogany and gaboon, while Douglas fir (British Columbian pine) and Finnish birch 
are prone to severe checking. It can be assumed, however, that the s pecies in general use are all liable to 
check when used outside. Checking affects only the surface layer of the outer veneer but, if the surface is 
painted, the cracks are communicated to the coating, allowing entry of moisture and failure of the paint fil m. 
 
C.3.1.2   Fibre building board, wood chipboard and plasterboard  
 
Painting of fibre building board, wood chipboard and plasterboard usually has a mainly decorative function, 
but it might be necessary for protection in some circumstances, e.g. with boards  used externally or in 
conditions of prolonged high humidity.  
 
There are four main types of fibre building board as follows.  
 
a) Hardboard. This is of a high density and presents a smooth, slightly absorbent surface upon which a 
satisfactory standard of fi nish can be obtained with most types of paint including gloss finishes. Hardboard is 
available in standard and tempered grades. Tempered hardboard is impregnated with  oils  or  resins  and  
heat-treated during  manufacture to  improve  its  water resistan ce. Some impregnation treatments can 
slightly retard the drying of solvent -borne paints, but this is rarely serious.  
 
b) Mediumboard. This is less dense and usually slightly more absorbent than hardboard but has a 
similarly smooth surface upon which a sati sfactory finish can be obtained with most paints including gloss 
finishes.  
 
c) Medium density fibreboard (MDF). This is manufactured by a dry process in which the primary bond 
is derived from a bonding agent. A smooth, slightly absorbent surface is present ed upon which a satisfactory 
finish can be obtained with most types of paint, including gloss finishes. Edges tend to be more absorbent 
and where exposed (e.g. by machining) and requiring a decorative finish, an additional coat of primer or 
sealer might be  required (see Table 18).  
 
d) Softboard. This is of low density and unless specially treated, e.g. surfaced or laminated, has a 
rough, highly absorptive surface upon which it is difficult to achieve a high standard of finish, especially with 
gloss finishes . 
 
In addition to factory -applied decorative treatments, including coatings and laminates, there are other 
treatments for fibre building boards which might affect painting. Typical treatments, and the types of boards 
to which they apply, are described as f ollows:  
 
a) Pulp  or  ivory  surface.  A  surface  layer  of  finely -ground  wood  fibre  is  incorporated  during 
manufacture and gives a uniform, light -coloured surface of low porosity. This facilitates direct application, 
without priming or sealing, of water -borne paints. The treatment is available on mediumboard and softboard.  
 
b) Sealed. A treatment which reduces absorption and might obviate the need to apply a primer or 
sealer on site. The treatment is available with standard hardboard.  
 
c) Primed. The board is supplied primed with a pigmented primer ready for site coating. The treatment 
is available with standard hardboard and softboard.  
 
d) Flame -retardant treatment. Chemical impregnation can render most boards flame retardant 
according to class 1 of BS 476 -7:1997, but see D.3. Boards are also available with a flame retardant  coating  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 125 on  one  or  both  sides.  Some  impregnation  treatments  can  affect  the appearance or behaviour of paint 
systems (see 8.2.2.3). The treatment is available with ha rdboard, mediumboard and softboard.  
 
e) Perforated. Boards might be perforated during manufacture to increase sound absorption as in 
acoustic tiles, or for other reasons, e.g. for decorative effect or to provide ventilation. When perforated 
boards or tiles  are used for their acoustic properties, it is important that the holes do not become blocked 
with paint; to prevent this, spray or roller application of thin coats is recommended. Perforated hardboard, 
mediumboard and softboard are available.  
 
C.3.1.3 Woo d chipboard  
 
Wood chipboard is composed of chips or particles of wood, mainly softwood, in a synthetic resin binder. It is 
sometimes described as particle board. Fungicidal, insecticidal and fire -retardant chemicals can be 
incorporated. Small amounts of pa raffin wax can be added to give limited protection against moisture 
absorption and consequent swelling of the wood chips.  
 
Other  factory -applied  treatments,  in  addition  to  decorative  finishes  such  as  surface  coatings, 
laminates and veneers, incl ude the following.  
 
a) Primed/filled. A paste filler/primer, off -white or grey in colour, is applied to one or both sides of the 
board. It provides a smooth, hard surface, receptive to most types of paint. Boards treated in this way and 
flame retardant acc ording to class 1 of BS 476 -7:1997 are available.  
 
b) Primed. A semi -transparent or opaque primer is applied to one or both sides of the board and 
obviates the need for site priming.  
 
c)     Sealed. A clear sealer, usually polyurethane -based, is applied to  one or both sides of the board.  
This gives protection against moisture penetration and also serves as a base for site -applied clear and 
pigmented coating systems.  
 
d) Paper -faced. Special resin -impregnated papers are applied to one or both sides of the bo ard and 
provide a satisfactory base for painting.  
 
   
126  © KEBS 2018 — All rights reserved  Annex D  
(informative)  
 
Fire 
 
 
D.1 General  
 
Three requirements for any fire to occur are:  
 
a) a fuel;  
 
b) an oxidizer (normally oxygen in the air);  
 
c) an ignition source.  
 
A complex interaction of many factors affects whether a fire occurs and what its characteristics are. Typically, 
for a solid fuel, an ignition source provides sufficient thermal energy to break chemical bonds in the fuel, 
resulting in the production of a range of volatile chemical spec ies that forms a gas or  vapour around the  
solid. A  proportion of  these  gases  or  vapours are flammable, i.e.  when combined with an oxidizer in the 
right ratio, can burn.  
 
Fire types have been broadly classified as smouldering or flaming but although  smouldering fires clearly 
occur at a much slower rate than flaming, the general principles still apply.  
 
D.2  Fire behaviour of coating and substrate  
 
The interaction of a coating film and substrate in determining fire behaviour is a function of both the 
flammability properties of the paint and the flammability properties and thermal conductivity of the substrate. 
For a given flammable paint system, substrates with a relatively high thermal conductivity (e.g. metals) tend 
to conduct heat away from the pain t film and can result in more difficult ignition and slower fire development. 
Substrates with a relatively low thermal conductivity (e.g. timber) might allow easier ignition and faster fire 
development.  
 
A further distinction between fires involving paint films and fires involving bulk fuels, is the relative importance 
of  heat release and surface spread of  flame. Both these parameters are important measurements in tests 
for fire safety. Generally, surface spread of flame is more important for paint films as the mass of paint film 
present is relatively small, and would produce a relatively low heat release.  
 
D.3 Fire testing and classification of construction products with coating films  
 
Attention is drawn to Building Regulations 2000: Approved Document B - Fire safety [39] which specifies the 
fire safety requirements for wall and ceiling surfaces in terms of class ratings. To conform to these 
requirements, products or systems have to be tested against either British Standard (BS) or European (EN) 
fire test procedures. For both types of procedure, fire tests are carried out on the substrate and paint film as 
a composite system.  
 
Historically, for painted surfaces, the main testing requirements for regulatory control have been centred on 
the BS 476 -7 (surface spread of flame) and BS 476 -6 (fire propagation). With the advent of the European 
Construction Products Directive, a new range of European harmonized tests has been developed, together 
with a classification system. These European tests, which include BS EN 13823, the single burning item test 
for measurement of heat release rate and surface spread of flame, can now be used as an alternative to the 
existing National Standard tests (e.g. BS 8202), and it is likely in the near future for Product Standards to be 
in place, allowing CE marking of construction products. The main distinction between the two testing regimes 
is that unlike the UK BS 476 tests, the European tests require products to be tested in their end use 
configuration. For example, for internal lini ng materials such parameters as substrate type, air gaps between 
substrate and backing, joint details, horizontal or vertical orientation have to be considered alongside the 
testing and classification result. Further, the production of burning droplets and  smoke can form part of the 
final classification for a product.  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 127  
With paint films there is an added complication in that decoration of surfaces with paint is likely to be a fairly 
frequent occurrence in buildings, whereas the testing and classification of the product might have only been 
performed on a single layer or limited layers of paint. This is being addressed by the use of the so -called 
"blue board" substrate, which has been developed to replicate the "worst -case scenario" in terms of a 
flammable mul ti-layer painted surface. This proprietary flammable "blue board" comprises 10 different coats 
of paint, applied to a plasterboard substrate.  
 
   
128  © KEBS 2018 — All rights reserved  Annex E  
(informative)  
 
Anti-graffiti treatments  
 
 
E.1 General  
 
All substrates are vulnerable to disfigurement by graffiti and present different types of problem for protection 
or removal. Masonry and concrete have characteristics that include porosity, which render removal 
particularly difficult, thus protective measures are important. New products are constantly emerging to protect 
surfaces but specialist advice is also needed.  
 
The main technical options for graffiti control on masonry and concrete can be classified under:  
 
a) removal:  
 
1) physical means;  
 
2) chemical means;  
 
b) prevention:  
 
1) new surfaces;  
 
2) established surfaces;  
 
3) cleaned surfaces;  
 
c) obliteration:  
 
1) by "normal" coatings;  
 
2) by selected graffiti resistant coatings.  
 
E.2 Removal  
 
The choice of materials and methods to remove graffiti will depend on many factors including the nature of 
the marker and the substrate.  
 
The range of markers used by "graffitists" is potentially very wide and could in principle include the most 
durable coating types. Although some graffitists do go to some lengths to use markers that resist removal 
(e.g. leather  dyes), the majority appear to use commercially available aerosol spray paints and felt 
permanent marker pens. The latter however are used more on smooth and already coated surfaces. In the 
case of paints the ease of removal will depend on whether they are  thermoplastic or cross -linked. The cross -
linking element is typically alkyd based. A range of commercial cleaners is available which includes such 
solvents as methylene chloride, methyl pyrrolidone, acetone, trichlorethene as well as acidic and alkaline 
solutions. They may be available in solution, paste, or bandage form. Within this range there is usually at 
least one that will be effective against commercial spray paints on smooth surfaces. However it is clear that 
this list includes many solvents that a re under severe and increasing environmental constraints for VOC and 
other reasons. Their continued availability cannot be assumed.  
 
The  effectiveness of  removal  will  depend on  the  contact time  of  the  solvent  and  is  aided  by 
mechanical methods  including scrapers and abraders. The use of water jet sprays can be effective, 
especially when hot (including steam), and can be further enhanced with various abrasives. Unfortunately 
with friable substrates such as concrete, this will also remove the sur face leaving a clean patch, which would 
contrast strongly with adjacent un -cleaned areas. High -pressure spraying brings in additional health and 
safety, as well as operational factors. The use of abrasive methods may only achieve the desired restoration 
effect if the whole area is cleaned. Clearly economics and practicality will limit this.  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 129  
In summary it may be observed that while there are physical/chemical means for removing most common 
graffiti markers, the porosity of untreated masonry and concrete sur faces allow penetration which renders 
total removal impossible. The adage "prevention is better than cure" applies and in vulnerable areas, 
surfaces need to be treated to resist application and aid removal.  
 
E.3 Prevention and damage limitation — anti-graffiti coatings  
 
E.3.1  General  
 
The objective of an anti -graffiti coating is to discourage disfigurement by markers in the first place and also to 
aid removal. If the coating is effective then discouragement arises from the experience of the graffitist when 
their efforts are easily removed. Discrete signs that such treatment has been carried out may aid this. A more 
obvious lack of surface wetting would also be a discouragement, and this may become more common as 
spray paints become water -borne. In principle,  inhibitors could retard drying of alkyd paints, and extend the 
period of relatively easy removal. However the main present purpose of anti -graffiti coatings is to aid 
removal.  
 
E.3.2  Sacrificial coatings  
 
Typically these are based on wax emulsions which are blended with siloxane acrylate, or fluoro compounds 
such as polyvinylidine chloride. Surfactants aid removal of the wax carrier, which may be removed by hot 
water jet. Some commercial systems have a special removal solvent. Systems bases on  solubilize d resins  
may  be  removed  with  mild  alkali.  Although these  coatings  are  nominally colourless, they  will  darken  
the  substrate to  a  degree, since  surface penetration reduces light scattering.  
 
Sacrificial coatings require re -coating after clea ning.  
 
E.3.3  Semi -permanent coatings  
 
These have a greater integrity than the sacrificial group and will contain typical acrylic resins as well as wax. 
The greater film integrity allows removal of the sacrificial coating with various removers, along with o ffending 
graffiti. The slightly higher build helps to physically block pores and prevent penetration by the graffiti marker.  
 
E.3.4  Permanent coatings  
 
Permanent coatings overlap with  conventional masonry paints  but  are  chosen to  have  greater resista nce 
to abrasion and chemical cleaning methods. They will therefore include high performance fluoro -acrylics and 
two component polyurethanes and epoxies. Such coatings needs to meet the various criteria for masonry 
coatings in terms of permeability and dura bility. An obvious disadvantage is that if they do become marked, 
by persistent graffiti or constant cleaning, then they will be difficult to remove, and continual overcoating 
would be impractical. On the other hand opaque permanent coatings (anti -graffiti  paint), may be  a  viable 
option for obliterating graffiti without the  need for removal. Conventional masonry paints can also be used 
for obliteration but will not be so readily cleaned if subject to further attack.  
 
The use of multi -colour finishes (7/1 4) may help to disguise residual graffiti marking.  
 
As an alternative to the high -build opaque treatment, some permanent low -build transparent systems are 
emerging which give long -term protection by lowering the surface energy.  
 
E.3.5  Application of anti -graffiti coatings  
 
Some anti -graffiti treatments need specialist application. Reference needs to be made to suppliers or 
independent sources that provide expertise on substrate suitability, selection of appropriate products, 
application and maintenance.  
 
   
130  © KEBS 2018 — All rights reserved   
Annex F  
(informative)  
 
Constituents of Coatings  
 
 
F.1 General  
 
Most coatings consist of binder, solvent or thinner and, in paints and stains, pigment. The binder is the non -
volatile film -forming constituent of the coating. The solvent or thinner imparts the required degree of flow to 
the binder during application; the combination of binder and solvent forms the vehicle or medium of the 
coating.  
 
Pigment provides colour and opacity and might have other functions in some types of coatings. Other 
constituent s might be present to ensure the stability of the coating or to prevent deterioration in storage or to 
confer specific characteristic performance attributes, e.g. UV resistance.  
 
F.2  Binders  
 
F.2.1   General  
 
The nature and proportion of binder present in a coating largely determines its characteristics, e.g. method of 
drying, compatibility with other coatings, application properties, degree of gloss, durability and resistance to 
attack. A characteristic of many binders is that they are dispersions or solut ions of synthetic or natural resins 
or polymers. Individual resins and other film -forming materials differ widely in properties and provide the 
basis for a great variety of coatings. The types of binder in general use are described in F.2.2 to F.2.7.  
 
F.2.2  Solvent -borne binders  
 
Many vegetable oils, notably linseed, soya and tung oils, dry slowly to form tough, elastic films when 
exposed to air. A few primers and finishes employ binders of this type but more commonly drying oils are 
chemically combined wi th resins to produce an oil -modified polyester, usually referred to simply as alkyds. 
These alkyds can be further modified by the inclusion of other resins, e.g. polyurethane, polyamide or 
silicone, to impart specific properties such as hardness, gloss ret ention, thixotropy or flexibility. Alkyds are 
used to produce clear coatings (varnishes) or, when pigmented, paints.  
 
Coatings  based  on  drying -oil type  binders  harden  by  reacting  with  oxygen  in  the  air  and  are 
characterized by being relativel y slow in drying and hardening compared with water -borne dispersions. The 
actual rate depends upon then* composition and the conditions of application, but typically they are dry to 
touch in 4 h to 8 h and re -coatable overnight. Initial drying and hardenin g is slower or can cease altogether in 
cold or damp conditions or in atmospheres where the movement of air is restricted. Drying and hardening 
can also be retarded by the presence of grease or dirt on the surface to which the coating is applied, and by 
some extractives in wood.  
 
Drying -oil and alkyd type coatings are traditionally organic solvent -thinned, usually with white spirit, although 
the  manufacturer's recommendations in  this  respect needs to  be  observed (see F.3). However, it is also 
possible t o solubilize or emulsify alkyds in water, thus moving them into the category of water -borne. 
Conversely, acrylic resins may be polymerized into aliphatic hydrocarbons by a process analogous to the 
"emulsion polymerization" referred to in F.2.3. These are d escribed as "non -aqueous dispersions" or NADs, 
and may be blended with solvent -borne alkyds.  
 
F.2.3  Water -borne binders  
 
The term "water -borne binders" covers a variety of polymer types carried in water as solutions, emulsions or 
dispersions. By far the mo st common are polymeric dispersions (e.g. vinyl, acrylic, styrene -acrylic) made by 
a process called "emulsion polymerization". This type of binder, and the paints derived from them, are often 
described as emulsion -binders, and emulsion paints. Strictly spe aking this term is incorrect, as the term 
emulsion is technically used to describe one liquid dispersed in another, such as the alkyd emulsions KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 131 described above. Water -borne dispersions are also sometimes described as "latexes" by analogy with 
natural rubbe r latex.  
 
Drying and hardening of water -borne dispersions proceed by evaporation of the water followed by 
coalescence of the particles. To aid the latter stage, many dispersions contain additional water - miscible 
solvents known as coalescing agents. In favourable circumstances, they are dry to touch or even re -coatable 
in 1 h to 2 h, and full washability is attained within a day or so of application. Damp atmospheres retard 
evaporation and cause delay in drying while very low temperatures can prevent coa lescence and produce an 
unsatisfactory film.  
 
Water -borne acrylic and vinyl dispersions were originally used mainly as coatings for walls and ceilings, but 
as a result of substantial technical development, they can compete with solvent -borne alkyds in most  sectors 
with the added advantage of low odour and VOC. Also, water, rather than expensive thinners, can  be  used  
for  thinning and  for  cleaning tools  and  equipment after  use. However, there are numerous detailed 
differences in areas, such as flow, grain -raising and poor penetration of wood, and initial gloss. Water -borne 
glosses have a lower gloss than alkyd paints, though their gloss retention is usually better.  
 
It is partly for this reason that there has been a growth in the use of water -borne al kyd emulsions, which 
combine some alkyd properties with the advantages of water. They still dry by auto -oxidation and will yellow 
and embrittle more on ageing than do acrylics.As a consequence of this, alkyd emulsions are sometimes 
blended with water -borne  acrylic dispersions to produce hybrid binders of intermediate properties. Such 
hybrids are used in some wood -coatings.  
 
F.2.4  Chemically -curing binders  
 
Coatings employing chemically -curing binders are supplied as two -pack materials, one container holding  the 
base and the other the appropriate quantity of curing agent, hardener or activator. The two components are 
combined shortly before use to induce a chemical reaction, which converts the applied film from a liquid to a 
solid state.  
 
Typical examples uti lize epoxy or polyurethane resins and are available as clear or pigmented coatings. 
These are resistant to chemical attack and abrasion but require high standards of surface preparation. 
Curing of the film is temperature -dependent and is slowed or can be i nhibited completely at low 
temperatures. These factors tend to limit the use of coatings of this type on building surfaces.  
 
Epoxy and polyurethane resins can be combined with other resins, notably alkyds, to produce one - pack 
materials, but these are not  
chemically -curing and do not have the degree of chemical and abrasion resistance characteristic of the two -
pack types.  
 
Two-pack chemically -curing binders are usually carried in solvent but some water -borne types are available.  
 
F.2.5  Lacquers  
 
In lacquer s, film -forming material is in solution (solution -binder), and conversion to the dry film is 
accomplished by evaporation of the solvent alone. Examples include solutions of shellac (knotting), vinyl -
type resins and nitrocellulose.  
 
The properties of lacque rs vary considerably, however, a general characteristic is that they tend to remain 
more or less soluble in the original solvent, which can create difficulties in applying several coats of the same 
material, especially by brush. Another characteristic is t heir rapid drying, which, again, can make them 
difficult or impossible to apply by brush to large areas.  
 
F.2.6  Inorganic (cement and silicate) binders  
 
White Portland cement forms the binding agent in cement paints for use on concrete, brickwork and simil ar 
surfaces. This type of coating is usually supplied in powder form and mixed with water immediately before 
use.   
132  © KEBS 2018 — All rights reserved   
In continental Europe, silicate -based masonry coatings, based on water -soluble silicate (e.g. potassium 
silicate) have been used for a consi derable tune. The coatings form inert, non -flammable films of 
considerable durability. The liquid paint is highly alkaline, hence pigmentation is normally by stable metal 
oxides resulting in a high order of colour stability.  
 
Some specialist coatings for the protection of iron and steel (see ISO 12944 and BS 5493) are based on 
silicates.  
 
F.2.7  Bituminous binders  
 
Bitumens and tars in solution or as emulsions are used in low -cost coatings, mainly for waterproofing. 
Suitable coal tar fractions are combined with epoxy resins in some specialist coatings (see Table 11).  
 
Coatings based on bituminous materials are usually black although, with some types, a limited range of dark 
colours is available. They can also bleed into and discolour other types of coatings applied over them (see 
8.15).  
 
F.3 Solvents and thinners  
 
F.3.1  General  
 
Solvent imparts the appropriate degree of flow, i.e. viscosity, to a paint to facilitate application. During the 
drying process, solvent evaporates and so determines the initial speed  of drying. Solvent vapours in the 
atmosphere can give rise to toxicity or flammability hazards (see Annex A).  
 
Coatings are generally supplied ready for use, although further additions of the recommended thinner by the 
user might be permissible, e.g. to a ssist the penetration of priming coats on absorbent surfaces or for 
application of coatings by spray.  
 
Over -thinning can seriously impair the opacity and other properties of coatings, but painting specifications 
need not preclude thinning; as indicated in the previous paragraph, thinning might be necessary in some 
circumstances. The specifications needs to state, however, that thinning is to be carried out under competent 
supervision and strictly in accordance with the manufacturer's recommendations as to t ype and proportion of 
thinner.  
 
F.3.2  Hydrocarbon solvents  
 
Hydrocarbon solvents are generally of the white spirit type, although aromatic hydrocarbons such as xylene 
or naphtha might be encountered occasionally. Conventional white spirit contains a mass f raction of about 
20% of aromatic hydrocarbons, but low aromatic solvents such as de -aromatized white spirit or isoparaffins 
are increasingly used. As well as having low odour, these solvents are considered to be less harmful.  
 
F.3.3  Oxygenated solvents  
 
Oxygenated solvents are derived from organic chemicals and small quantities might be included for specific 
purposes, e.g. help film formation in some water -borne paints. They are a major constituent of cellulose -
based paints and knotting solutions (see 7.4.3 ), and are also used in two -pack epoxy and polyurethane 
paints.  
 
F.3.4  Water  
 
Water -borne paints and bituminous emulsions are thinned using water. However, many water -borne paints 
contain some oxygenated solvent to give good low temperature film formation.  
 
F.4 Pigments  
 
F.4.1  General  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 133 The major function of the pigment is to provide colour and opacity. Additionally, and according to the nature 
of the pigments used, they can increase the thickness of the dry film, reinforce it physically, absorb or reflect 
harmful ultraviolet radiation, inhibit corrosion on metal surfaces or otherwise contribute to the durability or 
stability of the coating.  
 
A wide variety of pigments, differing in origin, colour and properties, are available. The principal categories 
are d escribed in F.4.2 to F.4.6.  
 
F.4.2  White pigments  
 
Because of the preponderant use of white and light -coloured finishes, white pigments are of considerable 
importance in the manufacture of paint. Titanium dioxide is the most widely used white pigment; it i s non -
toxic, has colour and opacity and is resistant to discoloration.  
 
NOTE  The use of white lead is restricted to use by specialists for the maintenance of listed historic 
buildings.  
 
F.4.3  Tinting pigments  
 
Tinting pigments comprise pigments that are us ed primarily for their colour when used alone or as tinters in 
combination with white, although some can have other properties. The main pigments in this category are 
natural or synthetic metal oxides, organic pigment dyestuffs and carbon black.  
 
Coloured pigments vary considerably in properties and, in  particular, in opacity. Some dyestuff pigments are 
relatively low in opacity and, with strongly coloured coatings based on pigments of this type, additional coats 
might be required (see Annex G).  
 
F.4.4  Extenders  
 
Extenders are inert materials, usually of mineral origin. Although generally classed as pigments, they might 
contribute little to the opacity of coatings but perform other useful functions such as reinforcing the 
mechanical strength of the dry film ; assisting application; imparting bulk or structure to the liquid paint and 
helping to prevent settlement of the solid ingredients during storage; improving intercoat adhesion or 
imparting roughness or texture to the coating when this is required.  
 
F.4.5  Corrosion -inhibitive pigments  
 
Corrosion -inhibitive pigments inhibit or retard the corrosion of ferrous and non -ferrous metals and are used in 
primers for these surfaces. They include metallic zinc and zinc phosphate.  
 
The properties of an inhibitive pigment can be influenced by the nature of the medium in which it is used. 
Metallic zinc is generally used in conjunction with oil -free binders of the solution or chemically - curing type, 
e.g. those based on chlorinated rubber or epoxy resin.  
 
NOTE  Red iro n oxide (red oxide), although having no inhibitive properties, is often used in conjunction with 
inhibitive pigments as a colouring agent. Due to their toxicity, lead and chromate pigments have a restricted 
range of uses.  
 
F.4.6  Laminar pigments  
 
Laminar p igments have a flaky structure and, within the paint film, the individual flakes lie parallel to the 
surface and overlap, forming a moisture barrier and improving tensile strength. Widely used pigments of this 
type include micaceous iron oxide (MIO), alumi nium and graphite. The two latter pigments, in addition to 
their general use in protective coatings, are also used in heat -resisting paints.  
   
134  © KEBS 2018 — All rights reserved  Annex G  
(informative)  
 
Paint colours  
 
 
The available pigments make possible a very wide range of colours although , in practice, the number of 
standard paint colours produced is restricted by economic considerations and, in some cases, by technical 
limitations. Paint manufacturers issue cards showing the standard colours in which their products are 
available. Some col ours might be unsuitable for exterior use, and the manufacturer's recommendations on 
this aspect need to be followed.  
 
BS 4800 is a range of colours for building paints, derived from BS 5252, which establishes a framework 
within which a number (237) of col ours have been selected as the source for all building colour standards 
and the means of co -ordinating them. Most paint manufacturers supply the full range of BS 4800 colours 
although not necessarily in all types of paints or from stock.  
 
A useful function  of paint is as a means of identifying the nature of piped services and the location of safety 
appliances by colour codes. BS 1710 and BS 5378 -2 give details of this application.  
 
House colours are used by many large organizations to give corporate identit y to buildings, equipment, 
vehicles, etc. Many standard colours of this nature used by official bodies are embodied in BS 381C.  
 
Texture influences the appearance of colours, and only to an approximate degree can a gloss colour be 
matched with that of a te xtured fabric. For accurate matching of colour, specimen and sample ought to be of 
the same finish and texture. Larger specimens than those normally given in colour cards need to be used for 
matching. Manufacturers might issue swatch books suitable for thi s purpose, and separate large cards of BS 
4800 colours are available from the British Standards Institution.  
 
Colours alter in drying: therefore, comparisons of colour in paint cannot be made until sample and match are 
both dry. The sample and the colour match made to it needs to be viewed in several forms of light, natural 
and artificial, since many pah's of colours which match in one illuminant appear to be quite different in colour 
in another. This effect is known as metamerism and usually derives from the choice of different pigment 
combinations used to prepare the comparison standard and the colour match.  
 
It is important when purchasing paint, that where ever possible different containers have the same batch 
numbers. Slight variations in colour could occur between different batches of paint which will be noticeable if 
the products are used in juxtaposition. If batching is not possible then different containers should either be 
intermixed in a larger vessel or individual batches used to complete whole s eparate elevations.  
 
Coloured pigments vary considerably in opacity, and, with many strong colours, especially those employing 
dyestuff pigments, special undercoats or additional finishing coats might be needed in order to achieve 
satisfactory appearance. The manufacturer's recommendations in this respect need to be followed and, 
where necessary, the use of special undercoats or additional finishing needs to be covered in the painting 
specification.  
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 135 Annex H  
(informative)  
 
Iron and steel  
 
 
H.1 Characteris tics 
 
Most forms of iron and steel, if not protected, tend to revert to their oxides by gradual combination with 
oxygen and moisture to form rust. In clean atmospheres, significant corrosion is unlikely unless the relative 
humidity exceeds about 70% but, i f there are sulfur compounds or other soluble salts (e.g. sea salt) in the 
atmosphere or on the surface, severe corrosion can occur at lower levels of relative humidity. Corrosion is 
likely to be more severe in humid industrial areas and near the coast rat her than in rural or urban areas.  
 
The micro -climate and factors such as orientation, degree of exposure and the flow of air over the surfaces, 
immediately surrounding the structure or component can increase or reduce the rate of corrosion. The 
frequency a nd extent to which condensation occurs, as a result of the difference in temperature between the 
metal and the air can also be relevant; in this respect, the thickness of the metal can be a significant factor.  
 
H.2 Cast iron  
 
The scale formed on cast iron is more adherent than the millscale on mild steel and has some protective 
value. If the scale is removed, cast iron corrodes at about the same rate as mild steel. This might not be 
immediately apparent because the corrosion process leaves behind a non -meta llic residue which largely 
retains the appearance of the original metal although its mechanical strength is negligible.  
 
H.3 Wrought iron  
 
In respect of painting, this is similar in characteristics to mild steel although its corrosion rate might differ 
slightly according to its composition.  
   
136  © KEBS 2018 — All rights reserved  Annex I  
(informative)  
 
Plaster  
 
 
I.1 General  
 
BS 1191 -1 distinguishes four grades of gypsum plasters  only two of which are in common usage: Grade A. 
Plaster of Paris. This is not normally used for plastering but is sometimes used for repairs  and might be 
gauged with lime or lime and sand. For painting purposes, it might be considered with grade B.  
 
Grade  B. Retarded hemi -hydrate plasters. These have a smooth, hard but moderately porous surface to 
which paint adhesion is good, but absorption is sometimes variable and can cause patchiness of water -
borne paints.  
 
Grade B plasters are generally neutral in rea ction and, even if gauged with lime, should not affect paint 
unless there is a source of alkali in the backing. Over -wetting during application can produce a powdery 
surface. In damp conditions (e.g. from prolonged heavy condensation or moisture penetratio n from behind), 
sweat out can occur, resulting in softening of the plaster and consequent paint failure.  
 
I.2  Lightweight plasters  
 
BS 1191 -2 describes lightweight gypsum undercoat and finish plasters based on grade B plasters with 
lightweight aggregates.  Their general characteristics, in relation to painting, are as described in  8.6.1.2. 
Premixed lightweight cement plaster undercoats can be used in some circumstances, and  these are strongly 
alkaline.  
 
Lightweight plasters initially  hold more  water  than   other types  and  can  take longer to  dry  out particularly 
in winter.  
 
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 137 Annex J  
(informative)  
 
Paper and wallcoverings  
 
 
J.1 General  
 
Papers and other wallcoverings comprise, first, those that are supplied uncoloured and that are intended to 
be painted and, secondly, existing coloured materials that might be suitable for painting in order that their 
appearance might be restored or that their colour might be changed. The mam types in each category are as 
follows:  
 
a) new and intended to be painted : 
 
1) lining papers;  
 
2) woodchip papers;  
 
3) relief wallcoverings;  
 
4) natural hessians (painting optional);  
 
5) blown vinyl wallcoverings;  
 
6) non-woven backed wallcoverings;  
 
7)  woven glass fibre paper. b)    existing coloured materials:  
 
i)    wallpap ers; 
 
ii)    paper -backed and sheet vinyls;  
 
iii)    coloured hessians;  
 
iv)    non -woven backed wallcoverings.  
 
No problems arise with materials in the first category in respect of painting, but problems can be experienced 
with some of those in the second  category, as indicated in 8.12.1.2 and 8.12.1.3.  
 
J.2 Plasterboard  
 
Plasterboard consists of a core of gypsum plaster with a thick paper liner on each side. Plasterboard can be 
skimmed with plaster after fixing, the surface then being painted as described  for plaster in  
8.6. It is also widely used in dry -lining systems in which paint or wallcoverings are applied directly to the 
board surface after fixing. Dry -lining systems usually involve special treatment of the joints between the 
boards.  
   
138  © KEBS 2018 — All rights reserved  Annex K  
(informative)  
 
Bricks, stone and concrete blocks  
 
 
K.1 Bricks and stone  
 
K.1.1  Clay bricks  
 
Most clay bricks contain soluble salts and these, in combination with water and the alkalis in cement mortars, 
can promote efflorescence (see 8.5.1.2). Clay bricks can be classified in general terms, by type, as common, 
facing and engineering bricks.  
 
a) Common bricks. These are usually plastered or rendered, but painting can be considered as a low -
cost alternative especially for interior walls. Paints of all types are l iable to failure by loss of adhesion when 
applied to Fletton common bricks externally. Failure occurs initially over kiss marks in the bricks, often within 
two years, and increases progressively; after four or five years, the paint on the whole of the bric k surfaces 
can be affected. Sand -faced and rustic Flettons are not  subject  to  paint  adhesion failures  to  any  great  
extent.  BRE  Information Paper  22/79, Difficulties in painting Fletton Bricks [40], recommends that external 
walls built with the i ntention of painting be of either sand -faced or rustic clay bricks or of calcium silicate or 
concrete bricks. It also gives recommendations for alternative treatments in situations where the extent of 
paint failure on walls already painted makes it not wor th attempting to maintain them in the painted state.  
 
b) Facing bricks. These are made or selected for their appearance, e.g. colour or texture. Adhesion of 
paint is usually satisfactory.  
 
c) Engineering bricks. These are dense, strong bricks made to defined limits of strength and water 
absorption. The adhesion of paints of conventional type to the virtually non -porous surface of bricks of this 
type is generally poor and, if painting is necessary, paints of the types recommended for glazed bricks (see 
8.14.2) needs to be used.  
 
K.1.2  Calcium silicate (sandlime or flintlime) bricks  
 
The surface of calcium silicate bricks is usually smoother than that of clay bricks although textured facing 
bricks are available. Paint adhesion is generally satisfactory.  
 
K.1.3  Concrete bricks  
 
Concrete bricks are strongly alkaline.  
 
K.1.4  Stone  
 
The many varieties of natural stone differ considerably in hardness and porosity, e.g. from virtually non -
porous granite or marble to porous limestone or sandstone. There might als o be differences in surface 
texture according to the method by which the stone is dressed or finished.  
 
K.2 Concrete blocks  
 
Precast concrete blocks are described in BS 6073 -1 and BS EN 772 -2. Their essential constituents are 
cement (usually ordinary or rapid -hardening Portland cement), a wide variety of aggregates and water. The 
main types of blocks are as follows.  
 
a) Aerated concrete blocks are usually made from mixtures of cement and siliceous materials, such as 
sand or pulverized fuel ash or a mixtur e of these, together with an aerating agent.  
 
 
b) Dense and lightweight blocks are made from cement and dense or lightweight aggregates, moulded 
and compacted by vibration or pressure.  
 KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 139 The aggregates used and the manufacturing process employed affects th e physical properties, surface 
texture and colour of the blocks. Surfaces can vary from coarse and open to fairly smooth and fine -textured. 
Colour is derived from the aggregates used, but pigments can be incorporated. Blocks are also available 
with a facto ry-applied coloured glaze that is resistant to staining and chemical attack.  
 
Provided that types having the appropriate properties are selected, concrete blocks are durable in most 
internal and external situations and are normally painted for aesthetic re asons or to facilitate cleaning. 
However, painting protection might be required where blockwork is exposed to severe driving rain. The 
natural appearance of some blocks might be acceptable without further treatment although clear coatings 
can be used to pr event staining or soiling.  
 
K.3 Cement -based sheets, boards and components  
 
K.3.1  General  
 
The sheets, boards and components to which this clause refers are manufactured from cementitious 
materials reinforced with fibres. They comprise:  
 
a) asbestos and fibre-cement goods;  
 
b) cement -based insulating boards, ceiling tiles and planks;  
 
c) glass fibre reinforced cement (GRC) cladding.  
 
K.3.2  Asbestos and fibre -cement goods  
 
WARNING Materials containing asbestos are subject to the legislation that requires p recautions to be taken 
in handling them to ensure that they do not constitute a hazard to health (see K.3.3 and Annex B).  
 
Asbestos and fibre -cement goods include roofing and cladding materials, lining sheets, decking tiles, 
rainwater goods and other compo nents. They are manufactured from Portland cement (CEM 1), asbestos or 
other fibre and water, compressed to a fairly high density.  
 
Asbestos -cement is a reasonably durable material, resistant to most forms of attack, and does not require 
painting for prote ction except in highly acidic atmospheres. In other situations, painting is mainly for 
appearance, to facilitate cleaning or to seal degraded surfaces to prevent loss of fibres. Asbestos -cement 
sheets and components supplied with factory -applied coatings h ave good chemical resistance.  
 
Fibre -cement shares many of the properties associated with asbestos -cement.  
 
Asbestos and fibre -cement is strongly alkaline when new and, if it is damp when painted or becomes so 
later, paints susceptible to alkaline attack ( see 8.5.1.4) are affected.  
 
If impermeable paint systems are applied to one side only of flat sheets or profiled sheets with large flat 
areas, differential carbonation can cause distortion and cracking of the sheets. This can be prevented by 
back -painting the sheets (see 8.11.1.4).  
 
K.3.3  Cement -based insulating boards, tiles and planks  
 
Cement -based insulating boards, tiles and planks can be made from Portland cement (GEM 1) and asbestos 
fibre, glass and other fibres (superseding asbestos, which might stil l be found in older material). Calcium 
silicate can also replace Portland cement (CEM 1) in some types.  
 
 
Cement -based insulating materials are less dense and more porous than asbestos and fibre -cement goods 
and are used principally as internal wall and ceiling linings. In the situations in which they are normally used, 
painting is essentially for appearance and to facilitate cleaning.  
  
140  © KEBS 2018 — All rights reserved  The materials, especially the types employing calcium silicate as a binder, are usually less alkaline than 
asbestos - and fibre-cement goods. Differential carbonation (see 8.11.1.44) is not a problem, and back -
painting is not therefore necessary.  
 
WARNING  Cement -based insulating materials containing asbestos fibre constitute a serious hazard to 
health and if found, should no t be disturbed. Unknown cement -based insulating materials should be treated 
as containing asbestos fibre until properly identified. Specialist advice  should  be  sought  on  the  treatment  
of  all  asbestos  containing  materials  and  if necessary the c orrect method for its safe removal and 
disposal.  
 
K.3.4  Glass fibre reinforced concrete (GRC) components  
 
Most GRC consists of Portland cement (CEM 1) matrix reinforced with glass fibre. There are a variety of 
GRC components, a major use being in sheets an d composite cladding panels, many with a factory -applied 
coating. The general requirements for site painting are as for other cement -based products.  
  KS 2791  :2018  
 
© KEBS 2018 — All rights reserved   
 141 Annex L  
(informative)  
 
Conditions Of application (temperature and humidity)  
 
The initial stage in the drying of most coatings is dependent, in varying degree, on the evaporation of solvent 
or thinner. Evaporation is slower in conditions of low temperature or high humidity, with a corresponding 
effect on the drying rate. In very hot conditions, the rate of evaporation can be so rapid as to cause difficulty 
in maintaining a wet edge (see 9.3.2.3).  
 
Solvent -borne coatings, especially gloss finishes, tend to become thicker and more difficult to apply at low 
temperatures, and this can result in the application o f excessively thick films which through - harden slowly or 
develop surface defects such as sagging or rivelling (wrinkling). High temperatures cause solvent -borne 
coatings to become thinner, and this can result in the application of excessively thin films.  
 
The drying of water -borne coatings depend almost entirely on evaporation of the water content and in highly 
humid conditions can be very slow, causing the coating to run or sag. With water -borne paints, formation of a 
homogeneous film, after evaporation o f the water, depends upon coalescence of the polymer particles. This 
can be inhibited at low temperatures, resulting in permanent impairment of film properties, notably 
washability and film strength.  
 
With two -pack epoxy, polyurethane and similar types of coatings, there is a secondary curing stage in which 
the full properties of the coating, e.g. of chemical resistance, are developed and this stage is temperature -
dependent. There might be a lower temperature limit below which application is not recommended . The pot -
life of two -pack coatings, i.e. the period during which they are usable, is also temperature -dependent, 
becoming shorter as temperature increases.  
 
Seasonal variations in temperature, humidity and general weather conditions can impose constraints  on the 
application of coatings, especially on external work. It is generally accepted that the optimum period for 
external painting in Great Britain is from mid -April to mid -September. However, the climate is sufficiently 
variable, geographically and from  year to year, for there to be frequent exceptions.  
 
Conditions are not always favourable during the period indicated, while there are other occasions during the 
remainder of the year when external painting could proceed without difficulty or detriment to the properties of 
coatings. Confining external painting strictly to the period traditionally regarded as most suitable can often be 
unduly restrictive.