10 PRESERVATION 

BRIEFS 

Exterior Paint Problems 

on Historic Woodwork 

Kay D. Weeks and David W. Look, AlA 

U.S. Department of the Interior 

National Park Service 

Cultural Resources 

Heritage Preservation Services 

A cautionary approach to paint removal is included in the guidelines to 'The Secretary of the Interior Standards for Historic Preservation 

Projects." Removing paints down to bare wood surfaces using harsh methods can permanently damage those surfaces; therefore such methods 

are not recommended . Also, total removal obliterates evidence of the historical paints and their sequence and architectural context. 

This Brief expands on that advice for the architect, building manager, contractor, or homeowner by identifying 

and describing common types of paint surface conditions 

and failures, then recommending appropriate treatments 

for preparing exterior wood surfaces for repainting' to 

assure the best adhesion and greatest durability of the new 

paint. Although the Brief focuses on resp.Q.rlsible methods 

of "paint removal," several paint surface conditions will 

be described which do not require any paint removal, and 

still others which can be successfully handled by limited 

paint removal. In all cases, the information is intended to 

address the concerns related to exterior wood. It will also 

be generally assumed that, because houses built before 1950 

involve one or more layers of lead-base paint,2 the majority of conditions warranting paint removal will mean dealing with this toxic substance along with the dangers of the 

paint removal tools and chemical strippers themselves. 

Purposes of Exterior Paint 

Paint3 applied to exterior wood must withstand yearly extremes of both temperature and humidity. While never expected to be more than a temporary physical shieldrequiring re-application every 5-8 years-its importance 

should not be minimized. Because one of the main causes 

of wood deterioration is moisture penetration, a primary 

purpose for painting wood is to exclude such moisture, 

thereby slowing deterioration not only of a building's exterior siding and decorative features but, ultimately, its 

underlying structural members. Another important purpose for painting wood is, of course, to define and accent 

architectural features and to improve appearance. 

Treating Paint Problems in Historic Buildings 

Exterior paint is constantly deteriorating through the processes of weathering, but in a program of regular maintenance-assuming all other building systems are functioning properly-surfaces can be cleaned, lightly scraped, 

and hand sanded in preparation for a new finish coat. Unfortunately, these are ideal conditions. More often, complex maintenance problems are inherited by owners of 

historic buildings, including areas of paint that have 

failed4 beyond the point of mere cleaning, scraping, and 

hand sanding (although much so-called "paint failure" is 

attributable to interior or exterior moisture problems or 

surface preparation and application mistakes with 

previous coats). 

Although paint problems are by no means unique to 

historic buildings, treating multiple layers of hardened, 

brittle paint on complex, ornamental-and possibly 

fragile-exterior wood surfaces necessarily requires an extremely cautious approach (see figure 1). In the case of recent construction, this level of concern is not needed 

because the wood is generally less detailed and, in addition, retention of the sequence of paint layers as a partial 

record of the building's history is not an issue. 

When historic buildings are involved, however, a 

special set of problems arises-varying in complexity 

depending upon their age, architectural style, historical 

importance, and physical soundness of the wood-which 

must be carefully evaluated so that decisions can be made 

that are sensitive to the longevity of the resource. 

Justification for Paint Removal 

At the outset of this Brief, it must be emphasized that 

removing paint from historic buildings-with the exception of cleaning, light scraping, and hand sanding as part 

of routine maintenance-should be avoided unless absolutely essential. Once conditions warranting removal have 

, General paint type recommendations will be made, but paint color recommendations are beyond the scope of this Brief. 

l Douglas R. Shier and William Hall, Analysis of Housing Data Collected in a LeadBased Paint Survey in Pittsburgh, Pennsylvania, Part 1, National Bureau of Standards, Inter-Report 77-1250, May 1977. 

, Any pigmented liquid, liquefiable, or mastic composition designed for application 

to a substrate in a thin layer which is converted to an opaque solid film after application, Paint and Coatings Dictionary, 1978, Federation of Societies for Coatings and Technology. 

4 For purposes of the Brief, this includes any area of painted exterior woodwork 

displaying signs of peeling, cracking, or alligatoring to bare wood. See descriptions of these and other paint surface conditions as well as recommended treatments on pp. 5-10. 
Fig. 1 Excessive paint build-up on architectural details such as 

this ornamental bracket does not in itself justify total paint 

removal. If paint is cracked and peeling down to bare wood, 

however, it should be removed using the gentlest means possible. 

Photo: David W. Look, AlA. 

been identified, the general approach should be to remove 

paint to the next sound layer using the gentlest means 

possible, then to repaint (see figure 2). Practically speaking as well, paint can adhere just as effectively to existing 

paint as to bare wood, providing the previous coats of 

paint are also adhering uniformly and tightly to the wood 

and the surface is properly prepared for repaintingcleaned of dirt and chalk and dulled by sanding. But, if 

painted exterior wood surfaces display continuous patterns 

of deep cracks or if they are extensively blistering and 

peeling so that bare wood is visible, then the old paint 

should be completely removed before repainting. The only 

other justification for removing all previous layers of 

paint is if doors, shutters, or windows have literally been 

"painted shut," or if new wood is being pieced-in adjacent 

to old painted wood and a smooth transition is desired 

(see figure 3). 

Paint Removal Precautions 

Because paint removal is a difficult and painstaking process, a number of costly, regrettable experiences have occurred-and continue to occur-for both the historic 

building and the building owner. Historic buildings have 

been set on fire with blow torches; wood irreversibly 

scarred by sandblasting or by harsh mechanical devices 

such as rotary sanders and rotary wire strippers; and 

layers of historic paint inadvertently and unnecessarily 

removed. In addition, property owners, using techniques 

that substitute speed for safety, have been injured by toxic 

lead vapors or dust from the paint they were trying to 

2 

Fig. 2 A traditionally painted bay window has been stripped to 

bare wood, then varnished. In addition to being historically inaccurate, the varnish will break down faster as a result of the sun's 

ultraviolet rays than would primer and finish coats of paint. 

Photo: David W. Look, AlA. 

Fig. 3 If damage to parts of a wooden element is severe, new 

sections of wood will need to be pieced-in. When such piecing is 

required, paint on the adjacent woodwork should be removed so 

that the old and new woods will make a smooth profile when 

joined. After repainting, the repair should be virtually impossible 

to detect. Photo: Morgan W. Phillips. 

remove or by misuse of the paint removers themselves. 

Owners of historic properties considering paint removal 

should also be aware of the amount of time and labor involved. While removing damaged layers of paint from a 

door or porch railing might be readily accomplished 

within a reasonable period of time by one or two people, 

removing paint from larger areas of a building can, with-
out professional assistance, easily become unmanageable 

and produce less than satisfactory results. The amount of 

work involved in any paint removal project must therefore be analyzed on a case-by-case basis. Hiring qualified 

professionals will often be a cost-effective decision due to 

the expense of materials, the special equipment required, 

and the amount of time involved. Further, paint removal 

companies experienced in dealing with the inherent health 

and safety dangers of paint removal should have purchased such protective devices as are needed to mitigate 

any dangers and should also be aware of State or local environmental and! or health regulations for hazardous 

waste disposal. 

All in all, paint removal is a messy, expensive, and 

potentially dangerous aspect of rehabilitating or restoring 

historic buildings and should not be undertaken without 

careful thought concerning first, its necessity, and second, 

which of the available recommended methods is the safest 

and most appropriate for the job at hand. 

Repainting Historic Buildings for Cosmetic 

Reasons 

If existing exterior paint on wood siding, eaves, window 

sills, sash, and shutters, doors, and decorative features 

shows no evidence of paint deterioration such as chalking, 

blistering, peeling, or cracking, then there is no physical 

reason to repaint, much less remove paint! Nor is color 

fading, of itself, sufficient justification to repaint a historic 

building. 

The decision to repaint may not be based altogether on 

paint failure. Where there is a new owner, or even where 

ownership has remained constant through the years, taste 

in colors often changes. Therefore, if repainting is 

primarily to alter a building's primary and accent colors, 

a technical factor of paint accumulation should be taken 

into consideration. When paint builds up to a thickness of 

approximately 1/16 " (approximately 16-30 layers), one or 

more extra coats of paint may be enough to trigger cracking and peeling in limited or even widespread areas of the 

building's surface. This results because excessively thick 

paint is less able to withstand the shrinkage or pull of an 

additional coat as it dries and is also less able to tolerate 

thermal stresses. Thick paint invariably fails at the 

weakest point of adhesion-the oldest layers next to the 

wood. Cracking and peeling follow . Therefore, if there 

are no signs of paint failure, it may be somewhat risky to 

add still another layer of unneeded paint simply for 

color's sake (extreme changes in color may also require 

more than one coat to provide proper hiding power and 

full color). When paint appears to be nearing the critical 

thickness, a change of accent colors (that is, just to 

limited portions of the trim) might be an acceptable compromise without chancing cracking and peeling of paint 

on wooden siding. 

If the decision to repaint is nonetheless made, the "new" 

color or colors should, at a minimum, be appropriate to 

the style and setting of the building. On the other hand, 

where the intent is to restore or accurately reproduce the 

colors originally used or those from a significant period in 

the building's evolution, they should be based on the 

results of a paint analysis. 5 

Identification of Exterior Paint Surface 

Conditions/ Recommended Treatments 

It is assumed that a preliminary check will already have 

been made to determine, first, that the painted exterior 

surfaces are indeed wood-and not stucco, metal, or other 

wood substitutes-and second, that the wood has not 

decayed so that repainting would be superfluous. For example, if any area of bare wood such as window sills has 

been exposed for a long period of time to standing water, 

wood rot is a strong possibility (see figure 4). Repair or 

replacement of deteriorated wood should take place before 

repainting. After these two basic issues have been 

resolved, the surface condition identification process may 

commence. 

The historic building will undoubtedly exhibit a variety 

of exterior paint surface conditions. For example, paint on 

the wooden siding and doors may be adhering firmly; 

paint on the eaves peeling; and paint on the porch 

balusters and window sills cracking and alligatoring. The 

accurate identification of each paint problem is therefore 

the first step in planning an appropriate overall solution. 

Paint surface conditions can be grouped according to 

their relative severity: CLASS I conditions include minor 

blemishes or dirt collection and generally require no paint 

removal; CLASS II conditions include failure of the top 

layer or layers of paint and generally require limited paint 

removal; and CLASS III conditions include substantial or 

multiple-layer failure and generally require total paint 

removal. It is precisely because conditions will vary at different points on the building that a careful inspection is 

critical. Each item of painted exterior woodwork (i.e., 

siding, doors, windows, eaves, shutters, and decorative 

elements) should be examined early in the planning phase 

and surface conditions noted. 

CLASS I Exterior Surface Conditions Generally Requiring 

No Paint Removal 

• Dirt, Soot, Pollution, Cobwebs, Insect Cocoons, etc. 

Cause of Condition 

Environmental "grime" or organic matter that tends to 

cling to painted exterior surfaces and, in particular, protected surfaces such as eaves, do not constitute a paint 

problem unless painted over rather than removed prior to 

repainting. If not removed, the surface deposits can be a 

barrier to proper adhesion and cause peeling. 

Recommended Treatment 

Most surface matter can be loosened by a strong, direct 

stream of water from the nozzle of a garden hose. 

Stubborn dirt and soot will need to be scrubbed off using 

1fz cup of household detergent in a gallon of water with a 

medium soft bristle brush. The cleaned surface should 

then be rinsed thoroughly, and permitted to dry before 

further inspection to determine if repainting is necessary. 

Quite often, cleaning provides a satisfactory enough result 

to postpone repainting. 

, See the Reading List for paint research and documentation information. See also 

Tilt? Sl?cretary of tilt? Interior's Standards for Historic Prt?ser..'atiotl Projects i.vitl, 

Guid,lilles for Applyillg the Stalldards for recommended approaches on paints 

and finishes within various types of project work treatments. 

3 
• Mildew 

Cause of Condition 

Mildew is caused by fungi feeding on nutrients 

contained in the paint film or on dirt adhering to any surface. Because moisture is the single most important factor 

in its growth, mildew tends to thrive in areas where 

dampness and lack of sunshine are problems such as 

window sills, under eaves, around gutters and downspouts, on the north side of buildings, or in shaded areas 

near shrubbery. It may sometimes be difficult to distinguish mildew from dirt, but there is a simple test to 

differentiate: if a drop of household bleach is placed on 

the suspected surface, mildew will immediately turn white 

whereas dirt will continue to look like dirt. 

Recommended Treatment 

Because mildew can only exist in shady, warm, moist 

areas, attention should be given to altering the environment that is conducive to fungal growth. The area in 

question may be shaded by trees which need to be pruned 

back to allow sunlight to strike the building; or may lack 

rain gutters or proper drainage at the base of the building. 

If the shady or moist conditions can be altered, the mildew 

is less likely to reappear. A recommend solution for 

removing mildew consists of one cup non-ammoniated 

detergent, one quart household bleach, and one gallon 

water. When the surface is scrubbed with this solution 

using a medium soft brush, the mildew should disappear; 

however, for particularly stubborn spots, an additional 

quart of bleach may be added. After the area is mildewfree, it should then be rinsed with a direct stream of water 

from the nozzle of a garden hose, and permitted to dry 

thoroughly. When repainting, specially formulated 

"mildew-resistant" primer and finish coats should be used. 

• Excessive Chalking 

Cause of Condition 

Chalking-or powdering of the paint surface-is caused 

by the gradual disintegration of the resin in the paint film. 

(The amount of chalking is determined both by the formulation of the paint and the amount of ultraviolet light 

to which the paint is exposed.) In moderation, chalking is 

the ideal way for a paint to "age," because the chalk, 

when rinsed by rainwater, carries discoloration and dirt 

away with it and thus provides an ideal surface for 

repainting. In excess, however, it is not desirable because 

the chalk can wash down onto a surface of a different 

color beneath the painted area and cause streaking as well 

as rapid disintegration of the paint film itself. Also, if a 

paint contains too much pigment for the amount of binder 

(as the old white lead carbonate/oil paints often did), 

excessive chalking can result. 

Recommended Treatment 

The chalk should be cleaned off with a solution of 1/2 

cup household detergent to one gallon water, using a 

medium soft bristle brush. After scrubbing to remove the 

chalk, the surface should be rinsed with a direct stream of 

water from the nozzle of a garden hose, allowed to dry 

thoroughly, (but not long enough for the chalking process 

to recur) and repainted, using a non-chalking paint. 

• Staining 

Cause of Condition 

Staining of paint coatings usually results from excess 

4 

Fig. 4 Paint films wear unevenly depending on exposure and 

location . Exterior locations which are susceptible to accelerated 

deterioration are horizontal surfaces such as window sills. These 

and similar areas will require repainting more often than less 

vulnerable surfaces. In the case of this window sill where paint 

has peeled off and adjacent areas have cracked and alligatored, 

the paint should be totally removed. Prior to repainting, any 

weathered wood should be rejuvenated using a solution of 3 

cups exterior varnish, 1 oz. paraffin wax, and mineral spirits/ 

paint thinner/ or turpentine to make 1 gallon. Liberal brush application should be made. This formula was tested over a 

20-year period by the U.S. Department of Agriculture's Forest 

Products Laboratory and proved to be just as effective as waterrepellent preservatives containing pentachlorophenol. After the 

surface has thoroughly dried (2-3 days of warm weather), the 

treated surface can be painted. A high quality oil-base primer 

followed by two top coats of a semi-gloss oil-enamel or latexenamel paint is recommended. Photo: Baird M. Smith, AlA. 

moisture reacting with materials within the wood substrate. There are two common types of staining, neither of 

which requires paint removal. The most prevalent type of 

stain is due to the oxidation or rusting of iron nails or 

metal (iron, steel, or copper) anchorage devices. A second 

type of stain is caused by a chemical reaction between 

moisture and natural extractives in certain woods (red 

cedar or redwood) which results in a surface deposit of 

colored matter. This is most apt to occur in new replacement wood within the first 10-15 years. 

Recommended Treatment 

In both cases, the source of the stain should first be located and the moisture problem corrected. 

When stains are caused by rusting of the heads of nails 

used to attach shingles or siding to an exterior wall or by 

rusting or oxidizing iron, steel, or copper anchorage 

devices adjacent to a painted surface, the metal objects 

themselves should be hand sanded and coated with a rustinhibitive primer followed by two finish coats. (Exposed 

nail heads should ideally be countersunk, spot primed, 

and the holes filled with a high quality wood filler except 

where exposure of the nail head was part of the original 

construction system or the wood is too fragile to withstand the countersinking procedure.) 

Discoloration due to color extractives in replacement 

wood can usually be cleaned with a solution of equal 

parts denatured alcohol and water. After the affected atea 
has been rinsed and permitted to dry, a "stain-blocking 

primer" especially developed for preventing this type of 

stain should be applied (two primer coats are recommended 

for severe cases of bleeding prior to the finish coat). Each 

primer coat should be allowed to dry at least 48 hours. 

CLASS II Exterior Surface Conditions Generally 

Requiring Limited Paint Removal 

• Crazing 

Cause of Condition 

Crazing-fine, jagged interconnected breaks in the top 

layer of paint-results when paint that is several layers 

thick becomes excessively hard and brittle with age and is 

consequently no longer able to expand and contract with 

the wood in response to changes in temperature and humidity (see figure 5). As the wood swells, the bond between paint layers is broken and hairline cracks appear. 

Although somewhat more difficult to detect as opposed to 

other more obvious paint problems, it is well worth the 

time to scrutinize all surfaces for crazing. If not corrected, 

exterior moisture will enter the crazed surface, resulting in 

further swelling of the wood and, eventually, deep cracking and alligatoring, a Class III condition which requires 

total paint removal. 

Recommended Treatment 

Crazing can be treated by hand or mechanically sanding 

the surface, then repainting. Although the hairline cracks 

may tend to show through the new paint, the surface will 

be protected against exterior moisture penetration. 

/ 

coat can sometimes result since, upon aging, the oil paint 

becomes harder and less elastic than the latex paint. If 

latex paint is applied over old, chalking oil paint, peeling 

can also occur because the latex paint is unable to penetrate the chalky surface and adhere. 

Recommended Treatment 

First, where salts or impurities have caused the peeling, 

the affected area should be washed down thoroughly after 

scraping, then wiped dry. Finally, the surface should be 

hand or mechanically sanded, then repainted. 

Where peeling was the result of using incompatible 

paints, the peeling top coat should be scraped and hand 

or mechanically sanded. Application of a high quality oil 

type exterior primer will provide a surface over which 

either an oil or a latex topcoat can be successfully used. 

fig. 6 Th is is an example of intercoat peeling. A latex top coat 

was applied directly over old oil paint and, as a result, the latex 

paint was unable to adhere. If latex is being used over oil, an ai/-

base primer should be applied first. Although much of the peeling latex paint can be scraped off, in this case, the best solution 

may be to chemically dip strip the entire shutter to remove all of 

the paint down to bare wood, rinse thoroughly , then repaint. 

Photo: Mary L. Oehrlein, AlA. 

Fig. 5 Crazing-or surface cracking-is an exterior surface condition which call be successfully treated by sanding and painting. • Solvent Blistering 

Photo: Courtesy, National Decorating Products Associatioll. Cause of Condition 

• Intercoat Peeling 

Cause of Condition 

Intercoat peeling can be the result of improper surface 

preparation prior to the last repainting. This most often 

occurs in protected areas such as eaves and covered 

porches because these surfaces do not receive a regular 

rinsing from rainfall, and salts from air-borne pollutants 

thus accumulate on the surface. If not cleaned off, the 

new paint coat will not adhere properly and that layer 

will peel. 

Another common cause of intercoat peeling is incompatibility between paint types (see figure 6). For example, 

if oil paint is applied over latex paint, peeling of the top 

Solvent blistering, the result of a less common application error, is not caused by moisture, but by the action of 

ambient heat on paint solvent or thinners in the paint 

film. If solvent-rich paint is applied in direct sunlight, the 

top surface can dry too quickly and, as a result, solvents 

become trapped beneath the dried paint film. When the 

solvent vaporizes, it forces its way through the paint film, 

resulting in surface blisters. This problem occurs more 

often with dark colored paints because darker colors absorb more heat than lighter ones. To distinguish between 

solvent blistering and blistering caused by moisture, a 

blister should be cut open. If another layer of paint is visible, then solvent blistering is likely the problem whereas if 

bare wood is revealed, moisture is probably to blame. 

Solvent blisters are generally small. 

5 
Recommended Treatment 

Solvent-blistered areas can be scraped, hand or mechanically sanded to the next sound layer, then repainted. In 

order to prevent blistering of painted surfaces, paint 

should not be applied in direct sunlight. 

• Wrinkling 

Cause of Condition 

Another error in application that can easily be avoided 

is wrinkling (see figure 7). This occurs when the top layer 

of paint dries before the layer underneath. The top layer 

of paint actually moves as the paint underneath (a primer, 

for example) is drying. Specific causes of wrinkling include: (1) applying paint too thick; (2) applying a second 

coat before the first one dries; (3) inadequate brushing 

out; and (4)" painting in temperatures higher than recommended by the manufacturer. 

Recommended Treatment 

The wrinkled layer can be removed by scraping followed 

by hand or mechanical sanding to provide as even a surface as possible, then repainted following manufacturer's 

application instructions. 

Fig. 7 Wrinkled layers can generally be removed by scraping anc 

sanding as opposed to total paint removal. Following manufacturers' application instructions is the best way to avoid this surface condition. Photo: Courtesy , National Decorating Products 

Association . 

CLASS III Exterior Surface Conditions Generally 

Requiring Total Paint Removal 

If surface conditions are such that the majority of paint will have to 

be removed prior to repainting, it is suggested that a small sample 

of intact paint be left in an inconspicuous area either by covering 

the area with a metal plate, or by marking the area and identifying 

it in some way. (When repainting does take place, the sample 

should not be painted over). This will enable future investigators to 

have a record of the building's paint history. 

• Peeling 

Cause of Condition 

Peeling to bare wood is most often caused by excess interior or exterior moisture that collects behind the paint 

6 

film, thus impairing adhesion (see figure 8). Generally 

beginning as blisters, cracking and peeling occur as moisture causes the wood to swell, breaking the adhesion of 

the bottom layer. 

Recommended Treatment 

There is no sense in repainting before dealing with the 

moisture problems because new paint will simply fail. 

Therefore, the first step in treating peeling is to locate and 

remove the source or sources of the moisture, not only 

because moisture will jeopardize the protective coating of 

paint but because, if left unattended, it can ultimately 

cause permanent damage to the wood. Excess interior 

moisture should be removed from the building through installation of exhaust fans and vents. Exterior moisture 

should be eliminated by correcting the following conditions prior to repainting: faulty flashing; leaking gutters; 

defective roof shingles; cracks and holes in siding and 

trim; deteriorated caulking in joints and seams; and 

shrubbery growing too close to painted wood. After the 

moisture problems have been solved, the wood must be 

permitted to dry out thoroughly. The damaged paint can 

then be scraped off with a putty knife, hand or mechanically sanded, primed, and repainted . 

Fig. 8 Peeling to bare wood-one of the m ost common types of 

paint failure-is usually caused by an interior or exterior 

moisture problem. Photo: Anne E. Grimmer. 

• Cracking/ Alligatoring 

Cause of Condition 

Cracking and alligatoring are advanced stages of crazing (see figure 9). Once the bond between layers has been 

broken due to intercoat paint failure , exterior moisture is 

able to penetrate the surface cracks, causing the wood to 

swell and deeper cracking to take place . This process continues until cracking, which forms parallel to grain , extends to bare wood. Ultimately, the cracking becomes an 

overall pattern of horizontal and vertical breaks in the 

paint layers that looks like reptile skin; hence, "alligatoring." In advanced stages of cracking and alligatoring, the 

surfaces will also flake badly . 

Recommended Treatment 

If cracking and alligatoring are present only in the top 

layers they can probably be scraped, hand or mechanically sanded to the next sound layer, then repainted. However, if cracking and/ or alligatoring have progressed to 
bare wood and the paint has begun to flake, it will need 

to be totally removed. Methods include scraping or paint 

removal with the electric heat plate, electric heat gun, or 

chemical strippers, depending on the particular area involved. Bare wood should be primed within 48 hours, 

then repainted. 

... 

-- Fig. 9 Cracking, alligatoring, and flaking are evidence of longterm neglect of painted surfaces. The remaining paint on the 

clapboard shown here can be removed with an electric heat plate 

and wide-bladed scraper. In addition, unsound wood should be 

replaced and moisture problems corrected before primer and top 

coats of paint are applied. Photo: Dav id W. Look, AlA. 

Selecting the Appropriate/ Safest Method to 

Remove Paint . 

After having presented the "hierarchy" of exterior paint 

surface conditions-from a mild condition such as mildewing which simply requires cleaning prior to repainting to 

serious conditions such as peeling and alligatoring which 

require total paint removal-one important thought bears 

repeating: if a paint problem has been identified that warrants either limited or total paint removal, the gentlest 

method possible for the particular wooden element of the 

historic building should be selected from the many available methods. 

The treatments recommended-based upon field testing 

as well as onsite monitoring of Department of Interior 

grant-in-aid and certification of rehabilitation projectsare therefore those which take three over-riding issues into 

consideration (1) the continued protection and preservation of the historic exterior woodwork; (2) the retention 

of the sequence of historic paint layers; and (3) the health 

and safety of those individuals performing the paint 

removal. By applying these criteria, it will be seen that no 

paint removal method is without its drawbacks and all 

recommendations are qualified in varying degrees. 

Methods for Removing Paint 

After a particular exterior paint surface condition has 

been identified, the next step in planning for repainting-if 

paint removal is required-is selecting an appropriate 

method for such removal. 

The method or methods selected should be suitable for 

the specific paint problem as well as the particular 

wooden element of the building. Methods for paint 

removal can be divided into three categories (frequently, 

however, a combination of the three methods is used). 

Each method is defined below, then discussed further and 

specific recommendations made: 

Abrasive-"Abrading" the painted surface by manual 

and/or mechanical means such as scraping and sanding. 

Generally used for surface preparation and limited paint 

removal. 

Thermal-Softening and raising the paint layers by applying heat followed by scraping and sanding. Generally used 

for total paint removal. 

Chemical-Softening of the paint layers with chemical 

strippers followed by scraping and sanding. Generally used 

for total paint removal. 

• Abrasive Methods (Manual) 

If conditions have been identified that require limited 

paint removal such as crazing, intercoat peeling, solvent 

blistering, and wrinkling, scraping and hand sanding 

should be the first methods employed before using 

mechanical means. Even in the case of more serious conditions such as peeling-where the damaged paint is weak 

and already sufficiently loosened from the wood surfacescraping and hand sanding may be all that is needed prior 

to repainting. 

Recommended Abrasive Methods (Manual) 

Putty Knife/ Paint Scraper: Scraping is usually accomplished with either a putty knife or a paint scraper, or 

both. Putty knives range in width from one to six inches 

and have a beveled edge. A putty knife is used in a pushing motion going under the paint and working from an 

area of loose paint toward the edge where the paint is still 

firmly adhered and, in effect, "beveling" the remaining 

layers so that as smooth a transition as possible is made 

between damaged and undamaged areas (see figure 10). 

Paint scrapers are commonly available in 1%6, 21/2, and 

3 lj2 inch widths and have replaceable blades. In addition, 

profiled scrapers can be made specifically for use on 

moldings. As opposed to the putty knife, the paint scraper 

is used in a pulling motion and works by raking the 

damaged areas of paint away. 

The obvious goal in using the putty knife or the paint 

scraper is to selectively remove the affected layer or layers 

of paint; however, both of these tools, particularly the 

paint scraper with its hooked edge, must be used with 

care to properly prepare the surface and to avoid gouging 

the wood. 

Sandpaper/ Sanding Block/ Sanding sponge: After manually 

removing the damaged layer or layers by scraping, the 

uneven surface (due to the almost inevitable removal of 

varying numbers of paint layers in a given area) will need 

to be smoothed or "feathered out" prior to repainting. As 

stated before, hand sanding, as opposed to harsher 

mechanical sanding, is recommended if the area is relatively limited. A coarse grit, open-coat flint sandpaper-the least expensive kind-is useful for this purpose 

because, as the sandpaper clogs with paint it must be 

discarded and this process repeated until all layers adhere 

uniformly. 

Blocks made of wood or hard rubber and covered with 

sandpaper are useful for handsanding flat surfaces. Sanding sponges-rectangular sponges with an abrasive aggregate on their surfaces-are also available for detail work 

that requires reaching into grooves because the sponge 

easily conforms to curves and irregular surfaces. All sanding should be done with the grain. 

7 
Summary of Abrasive Methods (Manual) 

Recommended: Putty knife, paint scraper, sandpaper, 

sanding block, sanding sponge. 

Applicable areas of building: All areas. 

For use on: Class 1, Class II, and Class III conditions. 

Health/ Safety factors: Take precautions against lead dust, 

eye damage; dispose of lead paint residue properly. 

Fig. 10 An excellent example of inadequate scraping before repainting, the problems here are far more than cosmetic. This improperly prepared surface will permit moisture to get behind the 

paint film which, in turn , will resu lt in chipping and peeling. 

Photo: Baird M. Smith , AlA. 

• Abrasive Methods (Mechanical) 

If hand sanding for purposes of surface preparation has 

not been productive or if the affected area is too large to 

consider hand sanding by itself, mechanical abrasive 

methods, i.e. , power-operated tools may need to be 

employed; however, it should be noted that the majority 

of tools available for paint removal can cause damage to 

fragile wood and must be used with great care . 

Recommended Abrasive Methods (Mechanical) 

Orbital sander: Designed as a finishing or smoothing toolnot for the removal of multiple layers of paint-the 

oribital sander is thus recommended when limited paint 

removal is required prior to repainting. Because it sands 

in a small diameter circular motion (some models can also 

be switched to a back-and-forth vibrating action), this 

tool is particularly effective for "feathering" areas where 

paint has first been scraped (see figure 11). The abrasive 

surface varies from about 3'X 7 inches to 4 X 9 inches and 

sandpaper is attached either by clamps or sliding clips. A 

medium grit, open-coat aluminum oxide sandpaper should 

be used; fine sandpaper clogs up 50 quickly that it is ineffective for smoothing paint. 

Belt sander: A second type of power tool-the belt sandercan also be used for removing limited layers of paint but, 

8 

in this case, the abrasive surface is a continuous belt of 

sandpaper that travels at high speeds and consequently offers much less control than the orbital sander. Because of 

the potential for more damage to the paint or the wood, 

use of the belt sander (also with a medium grit sandpaper) 

should be limited to flat surfaces and only skilled 

operators should be permitted to operate it within a 

historic preservation project. 

Fig. 11 The orbital sander can be used for lilllited paint removal, 

i. e., for smoothing flat surfaces after the majority of deteriorated 

paint has already been scraped off. Ph oto : Charles E. Fisher, III. 

Not Recommended 

Rotary Drill Attachments: Rotary drill attachments such 

as the rotary sanding disc and the rotary wire stripper 

should be avoided. The disc sander-usually a disc of 

sandpaper about 5 inches in diameter secured to a rubber 

based attachment which is in turn connected to an electric 

drill or other motorized housing-can easily leave visible 

circular depressions in the wood which are difficult to 

hide, even with repainting. The rotary wire stripper-clusters of metals wires similarly attached to an electric drilltype unit-can actually shred a wooden surface and is 

thus to be used exclusively for removing corrosion and 

paint from metals. 

Waterblasting: Waterblasting above 600 p .s.i. to remove 

paint is not recommended because it can force water into 

the woodwork rather than cleaning loose paint and grime 

from the surface; at worst, high pressure waterblasting 

causes the water to penetrate exterior sheathing and 

damages interior finishes. A detergent solution, a medium 

soft bristle brush, and a garden hose for purposes of rinsing, is the gentlest method involving water and is recommended when cleaning exterior surfaces prior to repainting. 
Sandblasting: Finally-and undoubtedly most vehemently 

"not recommended" -sandblasting painted exterior woodwork will indeed remove paint, but at the same time can 

scar wooden elements beyond recognition. As with rotary 

wire strippers, sandblasting erodes the soft porous fibers 

(spring wood) faster than the hard, dense fibers (summer 

wood), leaving a pitted surface with ridges and valleys. 

Sandblasting will also erode projecting areas of carvings 

and moldings before it removes paint from concave areas 

(see figure 12). Hence, this abrasive method is potentially 

the most damaging of all possibilities, even if a contractor 

promises that blast pressure can be controlled so that the 

paint is removed without harming the historic exterior 

woodwork. (For Additional Information, See Presevation 

Briefs 6, "Dangers of Abrasive Cleaning to Historic Buildings" .) 

Fig. 12 Salldblasting has permallently damaged this ornamental 

bracket. Evell paillt will not be able to hide the deep erosion of 

the wood. Photo: David W. Look, AlA. 

Summary of Abrasive Methods (Mechanical) 

Recommended: Orbital sander, belt sander (skilled operator only). 

Applicable areas of building: Flat surfaces, i.e., siding, 

eaves, doors, window sills. 

For use on: Class II and Class III conditions. 

Health/ Safety factors: Take precautions against lead dust 

and eye damage; dispose of lead paint residue properly . 

Not Recommended: Rotary drill attachments, high 

pressure waterblasting, sandblasting. 

• Thermal Methods 

Where exterior surface conditions have been identified 

that warrant total paint removal such as peeling, cracking, or alligatoring, two thermal devices- the electric heat 

plate and the electric heat gun-have proven to be quite 

successful for use on different wooden elements of the 

historic building. One thermal method-the blow torch- is 

not recommended because it can scorch the wood or even 

burn the building down! 

Recommended Thermal Methods 

Electric heat plate: The electric heat plate (see figure 13) 

operates between 500 and 800 degrees Fahrenheit (not hot 

enough to vaporize lead paint), using about 15 amps of 

power. The plate is held close to the painted exterior surface until the layers of paint begin to soften and blister, 

then moved to an adjacent location on the wood while the 

softened paint is scraped off with a putty knife (it should 

be noted that the heat plate is most successful when the 

paint is very thick!). With practice, the operator can successfully move the heat plate evenly across a flat surface 

such as wooden siding or a window sill or door in a continuous motion, thus lessening the risk of scorching the 

wood in an attempt to reheat the edge of the paint sufficiently for effective removal. Since the electric heat plate's 

coil is "red hot," extreme caution should be taken to 

avoid igniting clothing or burning the skin. If an extension 

cord is used, it should be a heavy-duty cord (with 3-prong 

grounded plugs). A heat plate could overload a circuit or, 

even worse, cause an electrical fire; therefore, it is recommended that this implement be used with a single circuit 

and that a fire extinguisher always be kept close at hand. 

Fig. 13 The electric heat plate (with paint scraper) is particularly 

useful for removing paint down to bare wood on flat surfaces 

such as doors, window frames, and siding. After scraping, some 

light sanding will probably be necessary to smooth the surface 

prior to application of primer and top coats. Ph oto: David W. 

Look, A lA. 

Electric heat gun: The electric heat gun (electric hot-air 

gun) looks like a hand-held hairdryer with a heavy-duty 

metal case (see figure 14). It has an electrical resistance 

coil that typically heats between 500 and 750 degrees 

Fahrenheit and, again, uses about 15 amps of power 

which requires a heavy-duty extension cord. There are 

some heat guns that operate at higher temperatures but 

they should not be purchased for removing old paint 

9 
because of the danger of lead paint vapors. The temperature is controlled by a vent on the side of the heat gun. 

When the vent is closed, the heat increases. A fan forces a 

stream of hot air against the painted woodwork, causing a 

blister to form. At that point, the softened paint can be 

peeled back with a putty knife. It can be used to best advantage when a paneled door was originally varnished, 

then painted a number of times. In this case, the paint 

will come off quite easily, often leaving an almost pristine 

varnished surface behind. Like the heat plate, the heat gun 

works best on a heavy paint build-up. (It is, however, not 

very successful on only one or two layers of paint or on 

surfaces that have only been varnished. The varnish simply becomes sticky and the wood scorches.) 

Although the heat gun is heavier and more tiring to use 

than the heat plate, it is particularly effective for removing paint from detail work because the nozzle can be 

directed at curved and intricate surfaces. Its use is thus 

more limited than the heat plate, and most successfully 

used in conjunction with the heat plate. For example, it 

takes about two to three hours to strip a paneled door 

with a heat gun, but if used in combination with a heat 

plate for the large, flat area, the time can usually be cut in 

half. Although a heat gun seldom scorches wood, it can 

cause fires (like the blow torch) if aimed at the dusty 

cavity between the exterior sheathing and siding and interior lath and plaster. A fire may smolder for hours before flames break through to the surface. Therefore, this 

thermal device is best suited for use on solid decorative 

elements, such as molding, balusters, fretwork, or "gingerbread." 

Fig. 14 The nozzle on the electric heat gun permits hot air to be 

aimed into cavities on solid decorative elements such as this applied column. After the paint has been sufficiently softened, it 

can be removed with a profiled scraper. Photo: Charles E. 

Fisher, III. 

10 

Not Recommended 

Blow Torch: Blow torches, such as hand-held propane or 

butane torches, were widely used in the past for paint 

removal because other thermal devices were not available. 

With this technique, the flame is directed toward the paint 

until it begins to bubble and loosen from the surface. 

Then the paint is scraped off with a putty knife. Although 

this is a relatively fast process, at temperatures between 

3200 and 3800 degrees Fahrenheit the open flame is not 

only capable of burning a careless operator and causing 

severe damage to eyes or skin, it can easily scorch or ignite the wood. The other fire hazard is more insidious. 

Most frame buildings have an air space between the exterior sheathing and siding and interior lath and plaster. 

This cavity usually has an accumulation of dust which is 

also easily ignited by the open flame of a blow torch. 

Finally, lead-base paints will vaporize at high temperatures, releasing toxic fumes that can be unknowingly inhaled. Therefore, because both the heat plate and the heat 

gun are generally safer to use-that is, the risks are much 

more controllable-the blow torch should definitely be 

avoided! 

Summary of Thermal Methods 

Recommended: Electric heat plate, electric heat gun. 

Applicable areas of building: Electric heat plate-flat surfaces such as siding, eaves, sash, sills, doors. Electric heat 

gun-solid decorative molding, balusters, fretwork, or 

"gingerbread." 

For use on: Class III conditions. 

Health/Safety factors: Take precautions against eye 

damage and fire. Dispose of lead paint residue properly. 

Not Recommended: Blow torch. 

• Chemical Methods 

With the availability of effective thermal methods for 

total paint removal, the need for chemical methods-in 

the context of preparing historic exterior woodwork for 

repainting-becomes quite limited. Solvent-base or caustic 

strippers may, however, playa supplemental role in a 

number of situations, including: 

• Removing paint residue from intricate decorative 

features, or in cracks or hard to reach areas if a heat gun 

has not been completely effective; 

• Removing paint on window muntins because heat 

devices can easily break the glass; 

• Removing varnish on exterior doors after all layers of 

paint have been removed by a heat plate/heat gun if the 

original varnish finish is being restored; 

• Removing paint from detachable wooden elements 

such as exterior shutters, balusters, columns, and doors 

by dip-stripping when other methods are too laborious. 

Recommended Chemical Methods 

(Use With Extreme Caution) 

Because all chemical paint removers can involve potential 

health and safety hazards, no wholehearted recommendations can be made from that standpoint. Commonly known 

as "paint removers" or "strippers," both solvent-base or 

caustic products are commercially available that, when 

poured, brushed, or sprayed on painted exterior woodwork are capable of softening several layers of paint at a 

time so that the resulting "sludge" -which should be 

remembered is nothing less than the sequence of historic 
paint layers-can be removed with a putty knife. 

Detachable wood elements such as exterior shutters can 

also be "dip-stripped." 

Solvent-base Strippers: The formulas tend to vary, but 

generally consist of combinations of organic solvents such 

as methylene chloride, isopropanol, toluol, xylol, and 

methanol; thickeners such as methyl cellulose; and various 

additives such as paraffin wax used to prevent the volatile 

solvents from evaporating before they have time to soak 

through multiple layers of paint. Thus, while some 

solvent-base strippers are quite thin and therefore unsuitable for use on vertical surfaces, others, called "semipaste" strippers, are formulated for use on vertical surfaces or the underside of horizontal surfaces. 

However, whether liquid or semi-paste, there are two 

important points to stress when using any solvent-base 

stripper: First, the vapors from the organic chemicals can 

be highly toxic if inhaled; skin contact is equally dangerous because the solvents can be absorbed; second, many 

solvent-base strippers are flammable. Even though application out-of-doors may somewhat mitigate health and 

safety hazards, a respirator with special filters for organic 

solvents is recommended and, of course, solvent-base 

strippers should never be used around open flames, lighted 

cigarettes, or with steel wool around electrical outlets. 

Although appearing to be the simplest for exterior use, 

a particular type of solvent-base stripper needs to be mentioned here because it can actually cause the most problems. Known as "water-rinsable," such products have a 

high proportion of methylene chloride together with emulsifiers. Although the dissolved paint can be rinsed off with 

water with a minimum of scraping, this ultimately creates 

more of a problem in cleaning up and properly disposing 

of the sludge. In addition, these strippers can leave a 

gummy residue on the wood that requires removal with 

solvents. Finally, water-rinsable strippers tend to raise the 

grain of the wood more than regular strippers. 

On balance, then, the regular strippers would seem to 

work just as well for exterior purposes and are perhaps 

even better from the standpoint of proper lead sludge 

disposal because they must be hand Scraped as opposed to 

rinsed off (a coffee-can with a wire stretched across the 

top is one effective way to collect the sludge; when the 

putty knife is run across the wire, the sludge simply falls 

into the can. Then, when the can is filled, the wire is 

removed, the can capped, and the lead paint sludge disposed of according to local health regulations). 

Caustic Strippers: Until the advent of solvent-base strippers, caustic strippers were used exclusively when a 

chemical method was deemed appropriate for total paint 

removal prior to repainting or refinishing. Now, it is more 

difficult to find commercially prepared caustic solutions in 

hardware and paint stores for home-owner use with the 

exception of lye (caustic soda) because solvent-base 

strippers packaged in small quantities tend to dominate 

the market. 

Most commercial dip stripping companies, however, 

continue to use variations of the caustic bath process 

because it is still the cheapest method available for removing paint. Generally, dip stripping should be left to 

professional companies because caustic solutions can 

dissolve skin and permanently damage eyes as well as 

present serious disposal problems in large quantities. 

If exterior shutters or other detachable elements are being sent out6 for stripping in a caustic solution, it is wise 

to see samples of the company's finished work. While 

some companies do a first-rate job, others can leave a 

residue of paint in carvings and grooves. Wooden elements may also be soaked too long so that the wood 

grain is raised and roughened, requiring extensive hand 

sanding later. In addition, assurances should be given by 

these companies that caustic paint removers will be 

neutralized with a mild acid solution or at least 

thoroughly rinsed with water after dipping (a caustic 

residue makes the wood feel slippery). If this is not done, 

the lye residue will cause new paint to fail. 

Summary of Chemical Methods 

Recommended, with extreme caution: Solvent-base strippers, caustic strippers. 

Applicable areas of buildings: decorative features, window 

muntins, doors, exterior shutters, columns, balusters, and 

railings. 

For use on: Class III Conditions. 

Health/Safety factors: Take precautions against inhaling 

toxic vapors; fire; eye damage; and chemical 'poisoning 

from skin contact. Dispose of lead residue properly 

General Paint Type Recommendations 

Based on the assumption that the exterior wood has been 

painted with oil paint many times in the past and the existing top coat is therefore also an oil paint, * it is recommended that for CLASS I and CLASS II paint surface conditions, a top coat of high quality oil paint be applied 

when repainting. The reason for recommending oil rather 

than latex paints is that a coat of latex paint applied 

directly over old oil paint is more apt to fail. The considerations are twofold. First, because oil paints continue 

to harden with age, the old surface is sensitive to the 

added stress of shrinkage which occurs as a new coat of 

paint dries. Oil paints shrink less upon drying than latex 

paints and thus do not have as great a tendency to pull 

the old paint loose. Second, when exterior oil paints age, 

the binder releases pigment particles, causing a chalky 

surface. Although for best results, the chalk (or dirt, etc.) 

should always be cleaned off prior to repainting, a coat of 

new oil paint is more able to penetrate a chalky residue 

and adhere than is latex paint. Therefore, unless it is 

possible to thoroughly clean a heavy chalked surface, oil 

paints-on balance-give better adhesion. 

If however, a latex top coat is going to be applied over 

several layers of old oil paint, an oil primer should be 

applied first (the oil primer creates a flat, porous surface 

to which the latex can adhere). After the primer has 

thoroughly dried, a latex top coat may be applied. In the 

long run, changing paint types is more time consuming 

and expensive. An application of a new oil-type top coat 

on the old oil paint is, thus, the preferred course of 

action. 

• Marking the original location of the shutter by number {either by stamping 

numbers into the end grain with metal numeral dies or cutting numbers into the 

end with a pen knife} will minimize difficulties when rehanging them. 

• If the top coat is latex paint {when viewed by the naked eye or, preferably, with 

a magnifying glass, it looks like a series of tiny craters} it may either be repainted 

with new latex paint or with oil paint. Normal surface preparation should precede 

any repainting. 

11 
If CLASS III conditions have necessitated total paint 

removal, there are two options, both of which assure protection of the exterior wood: (1) an oil primer may be applied followed by an oil-type top coat, preferably by the 

same manufacturer; or (2) an oil primer may be applied 

followed by a latex top coat, again using the same brand 

of paint. It should also be noted that primers were never 

intended to withstand the effects of weathering; therefore, 

the top coat should be applied as soon as possible after 

the primer has dried. 

Conclusion 

The recommendations outlined in this Brief are cautious 

because at present there is no completely safe and effective method of removing old paint from exterior woodwork. This has necessarily eliminated descriptions of 

several methods still in a developmental or experimental 

stage, which can therefore neither be recommended nor 

precluded from future recommendation. With the everincreasing number of buildings being rehabilitated, 

however, paint removal technology should be stimulated 

and, in consequence, existing methods refined and new 

methods developed which will respect both the historic 

wood and the health and safety of the operator. 

Special thanks go to Baird M. Smith, AlA (formerly Chief. Preservation Technology Branch, TPS) for providing general direction in the development of the 

manuscript. In addition, the following individuals are to be thanked for their 

contributions as technical experts in the field: Royal T. Brown, National Paint and 

Coatings Association, Washington, D.C.; Dr. Judith E. Selwyn, Preservation 'J"echnology Associates, Boston, Massachusetts; and Dennis R. Vacca, Pratt & Lambert 

Co., Carlstadt, New Jersey. Finally, thanks go to several National Park Service staff 

members whose valuable comments were incorporated into the text and who contributed to the production of the brief: James A. Caufield, Anne E. Grimmer, Jean 

E. Travers, David G. Battle, Sharon C. Park, AlA, Charles E. Fisher Ill, Sara K. 

Blumenthal, and Martha A. Gutrick. 

Reading List 

Batcheler, Penelope Hartshorne, "Paint Color Research and Restoration." 

Technical Leaflet 15. Nashville: American Association for State 

and Local History (undated). 

"Danger: Restoration May Be Hazardous to Your Health." The Old 

House Journal. Vol. 4, No.5 (May 1976), pp. 9-11. 

Gola, Edward F. "Avoiding Mistakes in Exterior Painting." The Old 

House Journal. Vol. 4, No . 6 (June 1976), pp. 1, 4-5. 

"How to Assure a Satisfactory Paint Job. " Scientific Section: Circular 

784. Washington, DC: National Paint, Varnish and Lacquer 

Association (undated). 

Labine, Clem. "Selecting the Best Exterior Paint." The Old House Journal. Vol. 4, No.7 (July 1976), pp. 1, 10-1l. 

Morton, W. Brown III and Hume, Gary L. The Secretary of the Interior's 

Standards for Historic Preservation Projects with Guidelines for 

Applying the Standards. Washington, DC: Department of Interior, 1979. 

Paint Problem Solver. St. Louis: National Decorating Products Association, 1980. 

"Special Issue: Exterior Painting." The Old House Journal. Vol. 4, No.4 

(April 1981), pp. 7l-94. 

Thorsen, John W. "Hazardous Waste : What is it? How to Handle it." 

Professional Decorating & Coating Action. Vol. 43, No.4 

(September 1981), pp. 4-5. 

This publication has been prepared pursuant to The Economic Recovery Tax Act 

of 1981, which directs the Secretary of the Interior to certify rehabilitations of 

historic buildings that are consistent with their historic character; the advice and 

guidance in this brief will assist property owners in complying with the requirements of this law. 

Preservation Briefs 10 has been developed under the technical editorship of Lee 

H. Nelson, AlA, Chief, Preservation Assistance Division, National Park Service, 

U.S. Department of the Interior, Washington, D.C. 20240. Comments on the 

usefulness of this information are welcomed and can be sent to Mr. Nelson at the 

above address. 

This publication is not copyrighted and can be reproduced without penalty. Normal procedures for credit to the authors and the National Park Service are appreciated. 

September 1982 

For snIp hy the Superilltpll(](l'ut of Document::;, U.S. Goyernment Printing Office 

" ·",hlng'toll. n.r. 20402