ICS 91.080.30   
 
Reference number  
DRS  211-6: 2021  
© RSB 2021  
  
 RWANDA 
STANDARD  DRS  
211-6  
 
Second  edition  
2021 -mm-dd 
 
Mortar for masonry — Test methods  —  
Part 6: Determination of adhesive strength 
of hardened rendering and plastering 
mortars on substrates  
   
DRS 211-6: 2021  
©RSB 2021  - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2021  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS 211-6: 2021  
iii                ©RSB 2021  - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ...................  iv 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ..................  1 
4 Principle  ................................ ................................ ................................ ................................ ........  1 
5 Apparatus  ................................ ................................ ................................ ................................ ...... 1 
6 Sampling and sample preparation  ................................ ................................ ..............................  3 
6.1 General  ................................ ................................ ................................ ................................ ..........  3 
6.2 Laboratory prepared mortars  ................................ ................................ ................................ ...... 3 
6.3 Ready to use mortars  ................................ ................................ ...... Error! Bookmark not defined.  
7 Preparation and storage of test specimens  ................................ ................................ ..............  3 
7.1 Substrate  ................................ ................................ ................................ ................................ ....... 3 
7.2 Application  ................................ ................................ ................................ ................................ .... 4 
7.3 Test areas  ................................ ................................ ................................ ................................ ...... 4 
7.3.1  General  ................................ ................................ ................................ ................................ ..........  4 
7.3.2  Fresh mortar  ................................ ................................ ................................ ................................ . 4 
7.3.3  Hardened mortars  ................................ ................................ ................................ .........................  4 
7.4 Storage and curing conditions  ................................ ................................ ................................ ... 4 
8 Procedures  ................................ ................................ ................................ ................................ .... 4 
9 Expression of results - Adhesive strength  ................................ ................................ ................  5 
Key 6 
10 Test report  ................................ ................................ ................................ ................................ ..... 7 
 DRS 211-6: 2021  
©RSB 2021  - All rights reserved                  iv 
 Foreword  
Rwanda Standard s are prepared  by Techni cal Committees and approved by Rwanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adopted 
by technical  committ ees are ratifie d by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS 211-6 was prepared by Technical Committee RSB/TC 009, Civil engineering and building materials . 
In the preparation of this standard, reference was made to the fo llowing standard s: 
1) BS EN 772 -11, Methods of test for masonry units — Part 11: Determination of water absorption of clay, 
aggregate concrete, autoclaved aerated concrete, manufactured stone and natural stone masonry units due 
to capillary action   
2) BS EN 998 -1:2016 , Specification for mortar for masonry – Part 1: Rendering and plastering mortar with 
inorganic binding agents   
3) BS EN 998 -2: 2016, Specification for mortar for masonry — Masonry mortar   
4) BS EN 1015 -2:1999+A1: 2006, Methods of test for mortar for masonry – Part 2: Bulk sampling of mortars 
and preparation of test mortars  
5) BS EN 1015 -12:2016 , Methods of test for mortar for masonry - Determination of adhesive strength of 
hardened rendering and plastering mortars on substrates  
The assistance de rived fro m the above source is hereby acknowledged with thanks.  
This second edition cancels and replaces the first edition (RS  211-6: 2010), clauses 5, 7, 8, of which ha s been 
technically revised.  
DRS 211 consists of the following parts, under the general title Mortar for masonry  —Test method : 
⎯ Part 1: Determination of particle size distribution (by sieve analysis)  
⎯ Part 2: Bulk sampling of mortars and preparation of test mortars  
⎯ Part 3: Determination of consistence of fresh mortar (by flow table)  
⎯ Part 4: Determination of consistence of fresh mortar (by plunger penetration)  
⎯ Part 5: Determination of flexural and compressive strength of hardened mortar  
⎯ Part 6: Determination of adhe sive strength of hardened rendering and plastering mortars on substrates  DRS 211-6: 2021  
v                ©RSB 2021  - All rights reserved  
 ⎯ Part 7: Determination of water absorption coefficient due to capillary action of hardened mortar  
 
Committee membership  
The following organizations were represented on the Technical Committee on Civil engineering  and building 
materials (RBS/TC 009)  in the preparation of this standard.  
Advanced Construction Technology Services (ACTS) - Rwanda  
CIMERWA   
City of Kigali   
Green Pact Africa   
Rwanda Inspectorate, Competition and Consumer Prot ection Authority (RICA)  
RTDA   
Standard Geotechnical Engineering and Construction Ltd (STAGECO Ltd)  
SJEC Ltd  
UR-CST  
Rwanda  Standards Board  (RSB) – Secretariat  
 DRS 211-6: 2021  
1                ©RSB 2021  - All rights reserved  
 Mortar for masonry — Test methods  — Part 6: Determination of adhesive 
strength hardened rendering and plastering mortars on substrates   
1 Scope  
This Draft Rwanda Standard provides a method for the determination of the adhesive strength between 
rendering plastering mortars and a substrate.  
2 Normative references  
The following documents are referred to in the text in such a way that some or all of  their content constitutes 
requirements  of this document.  For dated references, only the edition  cited applies. For undated references, the 
latest edition of the referenced document (including any amendments) applies.  
DRS 211-2, Mortar for masonry — Test methods  — Part 2: Bulk sampling of morta rs and preparation of test 
mortars   
DRS 211-3, Mortar for masonry — Test methods  — Part 3: Determination of consistence of fresh mortar (by 
flow table)   
CD 211-5, Mortar for masonry — Test methods  — Part 5: Determination of flexural and compressive strengt h 
of hardened mortar.   
3 Terms and definitions  
No terms and definitions are listed in this document . 
4 Principle  
The adhesive strength is determined as the maximum tensile stress applied by a direct load perpendicular to 
the surface of the rendering or plaster ing mortar on a substrate. The tensile load is applied by means of a 
defined pull -head plate glued to the test area of the mortar surface. The adhesive strength obtained is the 
quotient between the failure load and the test area.  
5 Apparatus  
5.1 Truncated conical rings , (see Figure 1) made of stainless steel or brass, with internal diameter of 50 
mm + 0.1 mm and 25 mm + 0.5 mm in height. The minimum thickness of the mould wall shall be 5.0 mm at the 
top. The external diameter at the base shall be 51 mm + 0.1 mm.  
5.2 Circular pull -head plates , made of metal , with diameter of 50 mm + 0.1 mm and minimum thickness 10 
mm, an d with central fitting for connection to the direct pull tensile force apparatus.  
 
  
©RSB 2021  - All rights reserved                  2 
  
Dimensions in millimetres  
  
Figure 1 — Sharp -edged, truncated conical ring  
5.3  Adhesive , based on resin, e.g. epoxy resin or methyl methacrylate resin.  
5.4 Core drilling machine , with core drill of nominally 50 mm internal diameter, suitable to cut core samples 
from hardened mortars and substrates.  
5.5 Testing machine , for direct pull tens ile force test and with suitable capacity and sensitivity for the test as 
specified in clause 9. It shall be capable of applying the load to the pull -head plate through a suitable fitting that 
excludes any bending forces. The machine shall comply with the requirements in Table 1.  
5.6 Storage chamber , capable of maintaining a temperature of 20 °C (+3/-2 °C)  and at a relative humidity of 
65 % + 5%.  
Table 1 — Requirements for testing machine  
Maximum permissible 
repeatability of forces 
as percentage of 
nomin al force %  Maximum permissible mean error of 
forces as percentage of nominal 
force  
% Maximum permissible error 
of zero of force of maximum 
force of range %  
2.0 ± 2.0  ± 0.4  
DRS 211-6: 2021  
3                ©RSB 2021  - All rights reserved  
  
6 Sampling and sample preparation  
6.1 General  
The fresh mortar for this test shall have minimum volume of 1.5 L or at least 1.5 times the quantity needed to 
perform the test, whichever is the greater, and shall either be obtained by reduction of the bulk test sample 
using a sample divider or by quarte ring or by preparation from water and the other constituents in the laboratory. 
Two test samples shall be prepared.  
6.2 Laboratory prepared mortars  
6.2.1 The length of mixing period shall be measured from the moment all the constituents are introduced into 
the mixer.  
6.2.2 The mortar shall be brought to a defined flow value as specified in  DRS  211-2 determined in accordance 
with DRS 211-3 and reported. The  test procedure shall not start until at least 10 min after completion of mixing 
and shall be concluded within the specified workable life of the mortar (preferably within 30min after completion 
of mixing.), unless otherwise instructed by the manufacturer.   
6.3 Mortars, other than laboratory prepared mortars  
Ready to use mortars (plant – made wet mortars which are retarded), and pre batched air -lime/sand wet mortars 
when not gauged with hydraulic binders, shall be used for specimen preparation within their spec ified workable 
life. Before testing, the batch shall be gently stirred by hand using a trowel or palette knife for 5 - 10 sec to 
counteract any false setting, but without any additional mixing of the batch. The flow value of the mortar in the 
bulk test sam ple shall be determined in accordance with DRS 211-3 as reported.  
7 Preparation and storage of test specimens  
7.1 Substrate  
7.1.1 For rendering or plastering systems manufactured for a specific background, i.e. clay or calcium silicate 
masonry units, concrete masonry unit, panels or cast in -situ concrete, etc., these materials, in an airdried 
condition, should be used as test substra tes. The water absorption due to capillary action of the units used in 
the substrate shall be recorded.   
7.1.2 Where no specific background is prescribed, rectangular concrete panels shall be used as substrate, 
with dimensions not less than 550 mm x 150 m m and 50 mm in thickness. The concrete shall be mixed with a 
water/cement ratio of 0.55 and using normal graded aggregates with maximum particle size of one third of the 
concrete panel thickness.  
7.1.3 The upper surface of the moulded substrate shall be l evelled and wood -floated to achieve a suitable 
surface. Within a period of 6 h - 24 h lightly brush the surface.   
7.1.4 The concrete panels shall have an age of not less than 28 days when applying the plastering or 
rendering system, the panels being cured under standardized conditions as described in RS 211 -5.   
©RSB 2021  - All rights reserved                  4 
 NOTE   Concrete panels as a substrate will normally give conservative adhesive strength values.  
7.2 Application  
The fresh mortar mix shall be applied to the prescribed substrate according to the manufac turer’s 
recommendations and the intended use. The substrate shall be kept vertical during application. Unless 
otherwise specified the total thickness of the mortar layer shall be 10 mm + 1 mm.  
7.3 Test areas  
7.3.1  General  
Circular test areas of approximately 50 m m in diameter shall be cut through the mortar layer, either in the fresh 
mortar according to 7.3.2 or in the hardened mortar according to 7.3.3. The diameter of the circular test area 
shall be recorded for each specimen. Five test specimens shall be provid ed.  
7.3.2  Fresh mortar  
7.3.2.1  After application and the initial setting of the mortar layer, the truncated conical rings ( 5.1), cleaned 
and lubricated with a thin layer of mineral oil, shall be pressed with their sharp edge, slightly rotating, through 
the fre sh mortar layer until full contact with the substrate is reached. The minimum distance between the rings 
and the free edges of the rendered substrate, and the free distance between the individual rings shall be 50 
mm.  
7.3.2.2  The rings shall be carefully removed, still slightly rotting, when the substrate is reached. If it is 
obvious that the adhesion of any of the cut specimens is disturbed during this preparation, another test specimen 
shall be cut. The specimen shall then be  stored as given in 7.4.  
7.3.3  Hardened mortars  
After curing of the rendering or plastering mortar, test specimens shall be cut using a core drilling machine (see 
5.4). The core shall be cut to a depth of approximately 2 mm into the substrate. Damaged specimen s shall be 
rejected.  
7.4 Storage and curing conditions  
When the mortar is sufficiently hard, the rendered specimens shall be enclosed within a sealed, air -tight 
polyethylene bag and at a temperature of 20 °C (+3/ -2 °C) for 7 d. The specimens shall subsequentl y be 
removed and stored in air ( 5.6) at a constant temperature of 20 °C (+3/ -2 °C) and at a relative humidity of 65 % 
+ 5% for a further 21 d.  
8 Procedures  
8.1 Glue the pull -heads with the adhesive centrally on the test areas, preventing any excess adhesive from 
bridging the cut around the test areas.  
8.2  Test the specimens at an age of 28 days immediately after being removed from the storing atmosphere.  DRS 211-6: 2021  
5                ©RSB 2021  - All rights reserved  
 8.3 Using the testing machine ( 5.5) apply the tensile load perpendicular to the test area through the pull head  
plates ( 5.2). Apply the load without shock and at a uniform rate. Use a rate such that the stress increases within 
the range of 0.003 N/mm2.s to 0.10 0 N/mm2.s) according to the expected adhesive strength and so that failure 
occurs between 20 s and 60 s (see Table 2). Record the failure load. Reject any test where the mode of failure 
is fracture at the adhesive layer between the pull -head plate and the mortar.  
Table 2 — Loading rate  
Expected adhesive 
strength  
(N/mm2)  Loading rate (N/mm2 s)  
< 0.2  0.003 - 0.010  
0.2 - < 0.5  0.011 - 0.025  
0.5 - 1.0  0.026 - 0.050  
> 1.0  0.050 - 0.100  
9 Expression of results - Adhesive strength  
9.1  Calculate the individual adhesive strengths from the following formula to the nearest 0.05 N/mm2.  
 
𝑓𝑢=𝐹𝑢
𝐴  
 
where  
𝑓𝑢 is the adhesive strength, (N/mm2);  
𝐹𝑢  is the failure load, (N); and  
A is the test area of cylindrical specimen, (mm2).  
9.2 Calculate the adhesive strength as the mean value from the individual values of the 5 specimens to the 
nearest 0.1 N/mm2.  
9.3 Possible fracture patterns leading to valid results are given in Figures 2 to 4 inclusive. Where fracture 
patterns occur as shown in Figures 3 and 4, i.e. where there is no failure at the mortar/substrate interface, 
results shall be considered as lower bound values. These values shall be valid for calculation of the mean value 
of adhesive strength.  
  
©RSB 2021  - All rights reserved                  6 
   
Figure 2 — Fracture pattern a — Adhesion fracture — Fracture at the interface between mortar and 
substrate. Test value equals the adhesive strength  
Key  
1 Pull-head plate  
2 Adhesive layer  
3 Mortar  
4 Substrate  
 
  
Figure 3 — Fracture pattern b — Cohesion fracture — Fracture in the mortar Itself. The adhesive 
strength is greater than the test value                                
 
DRS 211-6: 2021  
7                ©RSB 2021  - All rights reserved  
   
Figure 4 — Fracture pattern c — Cohesion fracture — Fracture in the substrate materia l. The adhesive 
strength is greater than the test value  
10 Test report  
The test report shall provide the following information:  
a) the place, date and time of taking the bulk test sample;  
b) the method used for taking the bulk test sample (if known) and the nam e of the organization that took it;  
c) the type, origin and designation of the mortar by reference to the relevant standard. d) preparation method;  
e) the type and description of the substrate including the coefficient of water absorption due to capillary 
action of masonry units (where relevant) comprising the substrate;  
f) any specialized treatment of the substrate in accordance with the manufacturer’s in structions; g) the 
date and time of testing;  
h) flow value of test mortar determined in accordance with RS 211 -3;  
i) details of test specimens including number, dimension, etc, if appropriate;  
j) individual values of adhesive strength rounded to the nearest 0.05  N/mm2 and the mean value rounded to 
the nearest 0.1 N/mm2 and description of mode of failure by reference to Figure 2 to Figure 4 inclusive; and  
k) remarks, if any.  
 
 
DRS 211-6: 2021  
 
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