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Peeling Paint? How to Diagnose, Correct, & Prevent Paint Failure on Buildings
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This article reviews common building exterior painting mistakes, describes how to diagnose paint failures on buildings, and outlines a procedure for field inspection of failed painted surfaces. We include photographs of paint failures on buildings and more photos of forensic paint laboratory examination of samples of failed paint useful to assist in diagnosing the probable cause of each type of paint failure. The examples use building exterior paint failures (and remedies), but many interior paint failures are similar their origin and cure, including general information provided by some paint manufacturers, home improvement suppliers, and by National Forest Products Laboratory experts. The diagnosis and cure of paint failure on buildings, particularly on wood siding and trim, is quite possible if there is a careful and thorough inspection of the building, its history, its surfaces, and the actual points of paint failure. It is diagnostic to compare the same coating on the same type of surface at different locations on a building and in areas of failed and not-failed paint. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

FAILURE CHECKLIST: EXTERIOR CLUES - Exterior Observations Related to Paint Failures

• Pattern, location, and type(s) of paint failure found
• Paint failure pattern variations, such as by building location, exposure, weather exposure, surface type, wall field, trim, columns, paint failures on horizontal surfaces vs. frequency of paint failures on vertical surfaces, paint failure depth, type of peeling, alligatoring, checking or cracking,, or blistering or chalking
• Appearance of surfaces from which paint has separated: mill gloss, chalking, old paint, wood fibers, moisture push.
• Mapping of failed and not-failed paint on various building areas, overlaid on the above list of possible causes.
• Sun/shade/rain/wind/mechanical-damage exposure of the building surfaces
• Surface drainage control
• Roof runoff control
• Evidence of paint or caulk-created moisture traps such as paint-sealed lap joints at heavily-painted wood clapboards.
• Other site water/moisture sources, dominant direction of wind-blown rain and snow
• Paint chip information (wood fibers, prior paint layers, mold, or debris present or absent on back of paint chips)
• Thickness of coating materials, number of paint layers, and identification of the layer which appears to be separating. Collect painted sample materials or paint chips which will permit measurement of the dry film paint thickness (DFT) which can be compared with the required wet film thickness (WFT) by calculation using the percentage of volume solids in the paint.
• Paint thinners: what thinners were allowed, in what quantities, and what thinners may actually have been used? Compare the quantity of paint invoiced to the job with the coverage rating per gallon or liter of the paint. See paint thickness notes above.
• Evidence of water infiltration into building cavities, such as ice dam leaks into walls, leaks at windows, or general indoor moisture and humidity levels and history, such as a history of wet basements, crawl spaces, attics, or specific building areas or rooms.
• Information about insulation, ventilation, vapor retarders, water and air barriers used on and in the building exterior walls.
• Signs of exterior mold (misnamed "mildew:") on building surfaces on the exposed surfaces, between paint layers, between the building surface and the failing or other paint coatings.
• Samples of paint used at the building, including liquid samples of primer and top coat, for possible further testing.
• Paint cans which held the current and prior paint used on building surfaces: for recording of the manufacturer or "paint brand", lot number, tinting information, date of manufacture, and the producer's storage, application, thinning, area coverage rating, % volume solids, recommended application thickness, and other technical information.
• Paint and thinner MSDS sheets, if they are available; usually you can find these documents online from the manufacturer.

FAILURE CHECKLIST: INTERIOR CLUES - Interior Observations Related to Paint Failures

• Signs of leaks or water entry from all sources, at all locations
• Relative humidity, use of humidifiers, dehumidifiers, hot air heat
• Construction details, air movement in the building
• Sources of water, leaks, moisture
• Sources of exfiltration - indoor air moving out through the building envelope
• Sources of infiltration - outdoor leaking into the building or into building cavities
• Information about insulation, ventilation, vapor retarders, water and air barriers
• Presence/absence of mildew, moisture stains, other signs
• Type of heating/cooling equipment installed (forced air, humidifiers, etc.)
• Fan placement and usage and effect on air movement
• Relationship of leaks or high humidity, vapor barrier defects, absent insulation, or other contributors, and areas of paint failure
• Placement and type of vapor barriers in building walls and ceilings
• Mapping of failed and not-failed paint on various building areas, overlaid on the above list of possible causes.

FAILURE CHECKLIST - SITE HISTORY Related to Paint Failures

• Building and Paint Job History
• Dates and type of construction of the building
• History of the paint failure: when was it first observed, where, in what form, and where has it increased - related to other events?
• Mapping of failed and not-failed paint on various building areas, overlaid on the above list of possible causes, e.g. different building areas painted at different times or with different coatings or primers.
• Documentation: was there an original job specification? are there any previous paint failiure investigation reports, field inspections, paint testing lab reports obtained to date. Collect records and dates of payment for the painting work, for the ordering and delivery of types and quantities of paints and other supplies.
• Dates and schedules of the entire painting procedure, from surface preparation through priming and top coating. Weather history prior, during, and after these dates; dates and weather history when paint failure was first observed.
• Sequence of building construction, events, floods, building left open, weather, rain, temperature, humidity at time of application of coatings, including halts or interruptions in the work by weather or other cause.
• Building Characteristics
• What is the substrate - on what surface or surface materials has the paint been applied?
• History of changes in the building: additions to the structure, additions or changes in insulation amount or type of material (One case I investigated had sound paint on the exterior of an 1850's farm house, until the new owners blew in wall insulation. The next spring most of the paint peeled off.)
• History of changes in the building's heating, cooling, plumbing systems, including change to or from forced-air heating/cooling, steam heat, hot water heat or cooling capacity or usage pattern such as when new occupants change the level of A/C usage.
• Painters
• What was the level of training, experience, and supervision of the painting crew?
• How large was the painting crew, which individuals peformed which tasks, how many individuals were applying paint at any given time, and on what different areas of the building.
• Is it possible to relate specific failures to an individual and thus to variation in surface preparation or paint application methods by worker?
• The size of the crew, schedule, paint quantities, and paint delivery schedule can assist in determining the order and rate of paint application and thus in evaluating the possible exposure of wet paint to specific weather or other site conditions on any given day during the painting project.
• Does the painting supervisor or contractor own and use a moisture meter? a wet film paint thickness gauge?
• Surface Preparation, Cleaning, and Testing
• What steps were taken in surface preparation, and how did these methods vary by area on the building? Surface Preparation, back priming, sanding, caulking details: what were the selected coatings and what is the coating compatibility.
• What was the use of primers, de-glossers, tinting agents, "mildewcides" (properly, fungicides), water-proofing compounds?
• Surface cleaning methods, chemicals, use of power washers, too close (damage marks), too far (not clean), inconsistently, or mis-aimed (blew water into walls)
• Where old paint was scraped, were edges feathered?
• How much old paint was left on the building? before application of primer or top coat by percentage area, and by differing building exposures and conditions?
• Were any paint tests performed before the building was painted? Was there a paint hardness test or a paint adhesion test performed?
• Paint Characteristics
• Paint mixing details: how was paint mixed, what methods were used? Were smaller containers dumped into a larger common container for mixing? Was all of each individual can content scraped into the mixer?
• Compatibility of paints and coatings used, vs. paints or coatings already on the surface
• What is the history of paint storage, purchase, and delivery for the specific containers of paint used at the building: was the paint exposed to unusual conditions such as high heat, prolonged storage, or freezing? Do the paint delivery schedule and quantities inform the investigator about the sequence and possible dates of paint application?
• What types of tinting agents, mildewcides, or other additives were used and what may have been their effects on the paint?
• What use was made of paint thinners?
• The Application of Paint to The Building
• Application or omission of primers, de-glossers, etc.
• Method of coating application (spray, roller, brush, factory)
• Sequence of painting and paint mixing, time between coats: What are the history, application sequence, and other details of paint or stain application: dates, conditions, substances applied, application equipment and methods.
• Paint quantities ordered and used: does the paint quantity invoiced and paid-for match the quantity reported to have been used on the building? Does the paint quantity actually used match the square footage of coated area when using the rated paint coverage per gallon?
• Painting Conditions, Weather
• Conditions at time of application of primer or paint, such as wet weather, high temperature, freezing weather, wind, fog, rain, early morning dew, nearby construction or other dust-making activity (mowing or leaf grinding).
• Did rain occur shorly before, during, or after application of paint?
• Document the highs, lows, and range of temperature, humidity, as well as rain, sun, and wind conditions

FAILURE INDICATORS - Paint Failure Indicators Where Demolition is Allowed

• Water sources and water traps in wall construction
• Damage from moisture/water/leaks/insects
• Type and installation details of insulation
• Type and installation details of vapor retarders, air barriers, water barriers
• Sources of air movement within walls and floors
• Evidence of (failure to apply) back priming of siding and end priming of siding
• Flashing and caulking errors
• Evidence of condensation in building cavities or on surfaces
• Evidence indicating whether moisture is moving from inside of structure out or outside of structure in
• Evidence indicating if wood clapboards were back primed, and leak stains on cavity side of building materials
• Mapping of failed and not-failed paint on various building areas, overlaid on the above list of possible causes.

Common Painting Mistakes to Avoid
ExteriorAPedia ^©

"The three key steps to successful painting are:
1. Prepare the surface,
2. Prepare the surface,
3. Prepare the surface."
- DF (moderator) and a panel of experienced house painters at ASHI ca1988 Paint Failures Seminar. But other than inadequate surface preparation, here are some other very common house painting mistakes:

BAD SURFACE PREP - Improper Surface Preparation Before Applying Paint

• removing only the obviously-loose paint, leaving poorly-secured paint, leaving thick edges of old paint where blisters or old peeled paint were inadequately removed.
• using paint to try to fill gaps where caulk should have been applied.
• using a spackling compound or filler intended for holes or cracks to "smooth" large building surface areas (skim coating) such as skim coating in order to apply paint over alligatored or poorly-adhered old paint. More thickness of fillers, paints, primers,or magic gluey coatings on the surface of un-sound paint are unlikely to work.
• painting over thinly-cracked, or peeling painted surfaces
• painting over old, existing thick, alligatored paint
• painting over dusty or dirty surfaces
• painting over mold (which many sources incorrectly call "mildew")
• painting over oily or other-contaminated surfaces
• painting over glossy hard paint surfaces without adequate preparation such as light sanding or use of a chemical de-glosser, likely to lead to an adhesion failure.
• painting over moldy surfaces without adequate cleaning and surface preparation such as power washing, disinfection, and light sanding, likely to lead to rapid mold re-growth in the paint and possibly to a paint adhesion failure, even if a paint "mildewcide" or fungicidal additive was used.
• painting over mill-glazed surfaces such as trim or cedar or pine clapboards
• painting over new masonry
• painting over old oxidized chalky paint or stain
• painting over rot or insect damaged- wood
• painting over silicone caulk (which in many cases is not paintable)
• painting the second coat before the first paint coating has adequately dried
• painting without reading the manufacturer's instructions for mixing, thinning, surface prep, temperature conditions, etc.
• surface preparation for painting by improper use of a power washer: spraying "up" on a clapboard building forcing water into the building wall cavities, (risking hidden mold contamination or a moisture problem leading to paint failure), or spraying too-close to the building surfacecauising gouging and undesirable loss of surface material
• surface washing using chemicals or bleach without adequate wash-off of the chemical or cleaner itself

SHORTCUT ERRORS - Painting Shortcut Errors

• Failing to mix the paint adequately. Poor mixing can result in an uneven distribution of paint vehicle and paint binder or uneven color distribution in the paint. Inadequate binder in sections of paint lead to early paint adhesion failures.
• Not putting paint on extra surfaces of wood to be painted on its exposed surface:
• omitting priming the back and ends and cut ends of clapboard siding
• omitting priming the back and ends of floor trim to be installed in a basement subject to moisture or damp floors
• skipping application of primer on new or incompatible surfaces
• over-thinning the paint to be applied (diluted binder)
• using a special purpose or shortcut super-fast drying primer or other primer not recommended by the manufacturer of the finish coating as the entire surface body primer

PAINT OVER MOISTURE - Painting Over Improper Surface Moisture or Painting Under Other Improper Weather Conditions

• painting over wet or damp surfaces such as from rain, morning dew, or interior leaks
• painting with a water-based paint (acrylic paint or latex paint) or any water borne paint when rain is expected soon. Typically the manufacturer requires at least four hours of drying time before expected rain. If rain arrives and wets the surface before the paint has been sufficiently dried, the paint coating is likely to be damaged, resulting in a reduced life and possibly pigment loss or adhesion failures.
• painting all surfaces after measuring for "ok" moisture or temperature on one area of a building, while ignoring variations in temperature, moisture, or condition of other surfaces
• painting directly on un-primed weathered, raw wood
• painting over cold surfaces or in cold weather (under 50 degF)
• hot surfaces or in hot weather (over 90degF for sure) - see PAINTING IN SUN and PAINTING IN WIND below.
• applying paint too thickly to the surface (runs, wrinkles)

INCOMPATIBLE PAINTS - Improper, Incompatible Paint Selection - Bad Chemistry

Paint failures can occur, such as failure of a paint to bond with a surface, failure of inter-coat bonding, or even dissolving of one paint coat by another, if incompatible paints are applied to a surface. For example, surfactant leaching can occur if there is an incompatibility between the primer coat and the finish coat. Paint chemists formulate primers and topcoats to work together as a tested and proven paint coating system.

• Painting a new coating on incompatible already-coated surfaces, including the paints or paint solvents: - applying a coating which is chemically incompatible with the existing layers. (Usually see wrinkling, staining, blistering, loss of adhesion, usually occurring while the new coating is still wet.)
• Applying paint where a stain or pigmented stain is more suitable, or without first applying the proper primer over a stained surface
• Using an indoor paint outside
• Omitting the first-coat primer or conditioner recommended by the top coat paint manufacturer
• Using a primer as a top-coat
• Contaminating varnish, shellac, or lacquer with moisture/water

WRONG PAINTS - Improper Paint Type Selection

There are lots of examples of using the wrong paint (besides the incompatible paints discussed above.

• Using an interior paint outdoors
• Using a paint which lacks the necessary attributes for a specific application - painting a wood siding paint on a metal water storage tank
• Painting an oil top coat over previous acrylic/latex top coats
• Using a defective paint which has been improperly formulated at the factory
• Using a defective paint which has been damaged due to improper storage, for example having been exposed to freezing

Be sure to follow the recommendations of your paint supplier and paint manufacturer in choosing the right paint for the proper application.

PAINTING IN SUN - Some Paints Fail If Applied in Direct Hot Sunlight

Depending on the chemistry and intended application of a particular paint, if applied to a too-hot surface (perhaps over 80 degF) the paint may form a skin which retards evaporation of the remaining carrier vehicle or solvent in the underlying paint. A possible result is the formation of paint blisters, some of which may rupture to form pinholes in the coating surface. A second possible result of painting on a too-hot surface is the formation of cracks in the painted surface where blisters have lifted and thinned the paint coating.

Blister cracks, like other cracks in a paint film, invite moisture penetration and later separation of the paint from the coated surface.

Coming: online photographs of blister cracking in an exterior paint

PAINTING IN WIND - Some Paints Fail if Applied in Windy Conditions

Depending on the chemistry and intended application of a particular paint, if applied in windy conditions, the paint may form a skim coat too rapidly, retarding evaporation and leading to cracking or blistering failure as just described above for the "painting in sun" case.

LIST OF FAILURES - Types of Paint Failures - Terminology
ExteriorAPedia ^©

Since no single reference listed all of the paint failure types, the list which follows is a collection, paraphrased and occasionally quoted from http://www.paint-worx.com/PaintFailure.htm with additions from http://www.bennette.com/pdf/whyfail.pdf, with added definitions and comments from the author, based on his field experience with house painting and paint failure investigations since 1978, and with forensic laboratory analysis of failed paint since 1986.

Adhesion loss - paint adhesion loss means the paint "lets go" of the surface onto which it was applied. This is usually due to poor surface preparation, application of primer or paint on oily, dirty, chalky, or dusty surfaces, or painting over a glossy surface [on glossy paint or on mill-glazed siding].

Paint adhesion failure due to use of incompatible paints: Paint adhesion loss may also occur if incompatible paints are used. Fatty acids to migrate through acrylic paint (and other) layers. This phenomenon even can be observed in oil paintings, as some pigments require and absorb more linseed oil than others. People in the art world know that one of the basic rules in applying painting is: always fatty on top of lean (highly bound on less bound media).

Paint adhesion failure due to gravity? One paint manufacturer's rep told our client that the paint was falling off of the house due to an "adhesion loss due to normal aging and gravity - a view which we consider nonsense. Gravity is not a significant factor in paint failure though once a paint chip has totally separated from a building surface, indeed it is the force of gravity which brings it away from the building and to a nearby horizontal surface or to the ground. If the adhesion principal failure were only "normal aging" then the paint should be failing uniformly wherever it was applied. Of course weather, including rain and sun exposure are indeed critical factors in paint wear and failure, and these forces are not uniform over surfaces at a building.

Alligatoring: [very common failure] cracked paint which resembles alligator skin. This is due to application of paint in too many layers. The inner paint layers have lost elasticity. As temperatures change and the building surfaces expand and contract, the old, brittle paint cracks. Alligatoring might also be caused by poor adhesion to a glossy surface, painting over an inadequately-dried first coat, or from weather exposure. Painting over an "alligatored" surface is futile. The older under-paint will continue to crack, causing failure of the new coating. Stripping off of the old paint down to bare wood is what's needed. Also see cracking, below for a distinction between these two similar failures.

Bleeding: this is a surface discoloration from water/water soluble dyes located in or on the painted surface, or on hardboard siding from wax in the siding. We often see this cosmetic defect when paint is applied over cedar siding as well; also see rusting.

Blistering: this very common failure is caused by moisture getting behind paint, or by painting over wet or damp surfaces.

Moisture blisters in paint usually occur when moisture evaporates to form a vapor bubble under an impermeable layer of paint, especially on new thin coatings or oil paint coatings.

Thermal blistering, or "temperature blistering" occurs when painting in sun, or if paint is applied to hot surfaces; the blister may be from moisture or solvents in the paint itself, when its outer skin dries before its inner layers, and the inner layer is heated. Both causes may occur together. Thermal blistering or paint solvent blisters look very different in the paint film from moisture-caused blistering. The microphotogaph shown here at 120x, taken in our laboratory, shows the edge of a microscopic paint blister, possibly solvent or thermal blistering. Often one cannot see this defect with the naked eye. Instead one observes paint cracking and adhesion failures on the painted surface. Microscopic laboratory analysis is required to complete the failure diagnosis. See our separate article on paint laboratory sample preparation for a procedure useful to prepare an edge-view of paint layers for microscopic examination.

Solvent blisters are small, usually microscopic. Where solvent blisters rupture they may leave pinholes in the paint or small craters. Usually ruptured solvent blisters leave craters surrounded by fine cracks radiating out from the crater.

Distinguishing solvent blisters from small moisture blisters:

Moisture blisters may be small, tend to occur behind the paint film after the paint is totally dry, are round or have rounded edges, separate the paint from the old surface uniformly, may bleed water when punctured, and can on occaion be extremely large, as much as 24" x the width of a clapboard. Moisture blisters in paint do not create pinholes, craters, nor crater-cracks. Like thermal blisters, solvent blisters may be an underlying mechanism for paint failure that cannot be seen by the naked eye. Where paint cracks around pinholes and blisters, paint adhesion failure may be observed.

The ultimate paint failure, loss of paint adhesion, may be due to paint shrinkage and movement over the surface or moisture penetration of the paint layers at pinholes and cracks. Paint which has failed in this manner may show other mechanisms of paint failure as well, such as separation of paint ingredients such as separation and bubbling of paint resins intended to function as adhesives, also key factors in the paint loss from the surface. These details become more apparent in the laboratory under forensic microscopic examination of samples of failing paint.

Blooming - (blushing) - this is moisture getting into varnish, shellac, lacquer. This coating failure leaves a milky opaque (usually-white) cloud on the coated surface.

Chalking - [common condition] weathered powdery exterior painted surfaces, may be normal, or may be premature if paint was excessively thinned or inadequately primed. Painting over a chalky surface means that the new paint will not adhere to the surface itself - since the oxidized "chalky" paint particles of the older coating interfere.

Chalk run-down - [common condition] is caused by chalking paint which runs down and stains other wall areas or masonry or foundations below. This cosmetic defect is most noticeable on an un-painted masonry wall below a painted surface such as a window, or wood siding above a brick wall. The oxidized paint which has washed onto the masonry surface can be mostly-removed by power washing, but don't damage brick masonry walls by using high pressure sand or water which can remove the glazed surface of the brick, leaving it vulnerable to future water and frost damage.

Cracking, Checking, Flaking, or Crazing - paint loses its elasticity, crazes, then cracks, especially where paint is thick or multi-layered. Also see "alligatoring" above. Cracks occur when paint is applied too thickly on the surface, or possibly when multiple layers of paint are present. Often the inner (older) layers of paint have lost elasticity and have already cracked, or form cracks which telegraph through the newer outer layer. Painting over such surfaces is likely to lead to failure as moisture invades the surface at cracks. This means that moisture gets behind the paint on the surface, thus eventually leading to paint failure. The distinction we make between "alligatoring" and "cracking" is this: "cracking" produces long, variegated and usually fairly thin openings in a painted surface. Cracking may occur even in a thinly painted surface. "Alligatoring" has a distinctive pattern in which the paint fissures form a rectangular pattern, each rectangle being perhaps less than 1/4" square, and always in thick old paint. (Beware of lead paint hazards when stripping old painted surfaces.

Chipping: paint breaks away from the surface due to poor surface preparation or possibly due to mechanical damage; painting over chalked surfaces can also cause this defect. If the failure is due to painting over a chalked surface the paint chips will expose an older painted surface below. If the failure is due to mechanical damage (such as a lawn-mower kicked-up stone), usually the chip exposes bare wood below.

Coverage: failure to cover or hide - usually due to poor paint mixing or poor color choice, such as trying to paint a light color over a dark surface in a single coat.

Dirt pick-up: dirt adheres abnormally to painted surfaces. Excluding dirt that collects on upper portions of exterior siding, e.g. from road and traffic dust [where roof eaves prevent rain from washing off this dirt] or from rain splash-up at ground level, paint may be tacky from improper solvents, paint incompatibility, or if the surface is indoors, inadequate drying ventilation.

Efflorescence and mottling. Effloresence is a white or yellowish [usually mineral] salt formed on masonry or plaster due to moisture migrating through the surface, evaporating, leaving mineral crystals behind. Effloresence is hygroscopic, and by attracting more moisture, will continue to accumulate. For some detailed photos of effloresence (sometimes mistaken for "mold") see www.inspect-ny.com/sickhouse/NotMold.htm

Fading - this is natural paint weathering due to the ultraviolet light (in sunlight); interior paints used on exterior surfaces may fade quickly [and are probably less weather resistant in general]. Often fading is accompanied by chalking.

Frosting - I associate this defect with a matte finish on paint that is supposed to give a smooth surface, possibly from chemical incompatibility with the existing coating on the surface.

Galvanized metal paint failure - poor adhesion to galvanized metal- paint peels or pits when painted on galvanized steel. This is a problem that occurs when painting over new galvanized metal or on rusty galvanized metal that has not been cleaned. See http://www.ppg.com/getpaint/etraining/solver/e_galvan.html. It is prevented by "curing" the galvanized metal before painting it. One approach is to let (outdoor) galvanized steel simply weather for a year. Some painters will etch the surface of the galvanized steel by washing it with a dilute acid such as vinegar. Beware that heating or oxidizing galvanized steel can release toxic gases.

Ghosting - this is caused by improper surface-priming, perhaps by too-thin application of the primer: walls are not absorbing paint uniformly. When the author was painting homes we avoided this issue by applying primer uniformly and not spreading it too thin, and if ghosting was visible in the primer coat we added a second primer coating. An assistant who tired to "stretch" the paint too far, thinking he was economizing, created such bad ghosting on one project that we had to paint an entire interior over again. It would have been much cheaper not to have spread the paint so thinly in the first place. We also see a similar defect if a paint roller is too dry when applying paint over a surface.

Gloss - loss of: this is due to improper priming where old paint was removed; high surface porosity also causes loss of gloss as does paint applied in damp or foggy weather. A glossy paint will be low-gloss or nearly flat if the paint was over-thinned. Also see http://www.ppg.com/getpaint/etraining/solver/e_gloss.html cites painting in sun, using interior paint outside, or poor quality paint as causes for loss of gloss.

Hatbanding or "Lapping"- is caused by thick paint applied at multiple layers where cutting in `(usually) of interior walls, ceilings , and corners, or use of excessively long roller naps. We see this quite often where a ceiling or wall corner is cut-in to the rest of the painted field using a brush, and then the field of the painted area is covered using a roller. It is a cosmetic defect.

Hardboard siding staining or "wax bleed" is cited by Lowes and PPG, and refers to waxes in composite siding [such as "Masonite (TM)" hardboard which bleeds (usually a brown stain) to the surface if a proper surface sealant was not used as a primer. Such stains may be mistaken for mold. See http://www.lowes.com/lowes/lkn?action=howTo&p=Improve/WaxBleed.html&rn=RightNavFiles/rightNavPaint

Masonry paint failure: Poor alkali resistance - this refers to color loss and paint deterioration on masonry, possibly caused by painting over new masonry such as a recent pour of concrete. See http://www.ppg.com/getpaint/etraining/solver/e_alkali.html. Also see Efflorescence.

Mildew [Mold]: dark or colored spots or shading in paint caused by mold growth, particularly in damp or shaded areas. Molds which are mis-names as "mildews" in this case are growing on nutrients in paint, varnish, or on organic debris on the coated surface. Some coatings such as oils and linseed oil-based paints are particularly mold-friendly. Many modern paints contain "mildewcide" to reduce this effect or it can be added [beware it's probably a serious toxin.] Acrylic latex paints are more mildew resistant. Good surface prep is important. Actually real "mildew" will never be found on painted surfaces. Mildew will be a member of one two groups, "Downy" or "Powdery" but in any case mildew is an obligate parasite which grows only on living plants. What people call "mildew" on painted surfaces is mold. Unless your walls are covered with grapes, its not "mildew." Not that that's much consolation. In some cases other small black spots on a wall might have been put there by "artillery fungus" a mold genera which shoots small black sticky spores onto a surface from its nearby point of growth. In this case the paint is not at all at fault. Finally, small black spots may appear on a painted surface where vines have been removed and where the vines' attachment points pulled off paint or left organic debris behind when the vines were removed. A close look is needed to distinguish these patterns on a wall. Artillery fungus spots are likely to be close to the ground-only. Vine spots and damage will follow a vine-growth pattern up the wall from the ground. Mold growing on a painted surface is often keyed to areas of shade and moisture exposure.

Mill gloss is a hard shiny surface left on wood clapboards or wood trim as a result of the lumber milling process. A high-speed rotating planer or cutting blade which is used to impart a flat smooth finish to (usually one) side of a wood clapboard, or to interior wood trim can leave the surface of the wood hard and shiny. Unless this "gloss" is broken by light sanding there is risk of poor paint or stain penetration of the wood surface and thus a failure of the coating to adhere to the surface of the wood. -- DJF.

Nail head rusting - occurs where nails on a surface are painted over, usually with a water-based paint, which rusts the nail head. It can be prevented by setting and puttying over old rusty nails, by sealing nail heads with a lacquer-primer before painting the surface, or by using stainless or galvanized nails in the first place. Even galvanized nails may rust, however, if the impact of the hammer cracks the galvanized coating on the nail.

Overlapping - �see hatbanding or lapping above. This also occurs on exterior or interior surfaces where paint is allowed to dry and then newly-applied paint overlaps the dried section as the next area is painted. When the author was painting houses we reduced this hazard (particularly indoors) by rolling out an increasingly thin coat at the edge of a section which we know is likely to dry before getting back to continue with new paint. Using a paint roller that is very wet for the last edge of a section is likely to leave a ridge of thick paint that will show overlapping when painting continues.

Paint incompatibility - may be a cause of peeling, blistering, wrinkling, or other failures. Be sure to read the manufacturer's label and to either determine what paint is already on a surface to be re-painted, or review your choices with a paint expert.

Peeling - �strips or sections of paint peel loose from the surface, usually due to moisture and/or inadequate surface preparation. Some inspectors mix descriptions of "blistering" and "peeling" but since the causes and remedy differ the distinction can be important.

Rusting - painted metal surfaces such as nail heads show through the new paint, perhaps where metal is exposed to moisture from the paint itself if a water-based paint is used.

Resin Failure - paint resins separate out from the paint mixture, perhaps due to improper paint formulation, improper paint mixing, combining incompatible paints, or exposure to high temperatures during drying. This defect is completely invisible on the painted surface and on failing paint chips, but it can be quite apparent during forensic microscopic examination of paint chips in the laboratory, as shown in the lab photograph here.

Sagging or Running occur when paint is applied over glossy surfaces, or due to excessive paint thinning, due to application of too much paint on the surface, due to paint being applied to a dirty surface or being applied in weather below the recommended temperature. Proper application of paints and surface preparation will eliminate sags and runs. This is sometimes an indication of an inexperienced painter.

Skim Coat - skim coating of building exterior surface which is in poor condition is not a reliable painting preparation method and is likely to lead to cracking failures in the skim-coated, painted surface, as shown in these photos.

Spalling is flaking chipping of masonry surfaces. On painted masonry moisture may be entering the surface through cracks or holes (or other routes) and getting behind the paint. Winter freeze-thaw cycles (obviously only in cold climates) cause the wet substrate to freeze, expand, and chip off. We've also seen this defect on brick walls which were tuck-pointed using a mortar with too much portland cement. Acrylic surface conditioners (primers) can reduce this effect.

Spotting, brown or other stains bleeding through new paint - "surfactant leaching" - can cause spotting, possibly from painting a cool or damp surface or painting in cool or cold conditions. See http://www.mcphersonpainting.com/leaching.htm and also http://www.mcphersonpainting.com/tannin.htm which cites tannin staining, when tannic acid, such as oils in pine knots or cedar bleed through new paint. Also see Rusting above.

Surfactant leaching,: surfactants are chemicals added to paints to improve paint flow and or to aid in formation of an emulsion. As I stated above at "incompatible paints", surfactant leaching can occur, for example, if there is an incompatibility between the primer coat and the finish coat. Paint chemists formulate primers and topcoats to work together as a tested and proven paint coating system.

Tackiness and slow-dry - is caused by painting a second coat too soon, or painting in wet or foggy weather, or applying paint onto a damp surface. If using an alkyd, painting in an enclosed, un-vented area the painter can also cause this condition.

Thickness failures of painted surfaces: paint can build up to an excessive thickness, leading to cracking and peeling when a new coat is applied, as the under-coats have lost elasticity, or trap moisture or debris between paint layers.

Vinyl siding paint failures - warping is caused by painting a light colored siding with dark paint, (overheating in sun exposure), probably aggravated by improper siding installation (nailed too tightly to the wall). Some paints are formulated specifically to adhere to vinyl siding but may still peel if the siding was painted while wet or dirty. We've also seen plastic trim become deformed on metal entry doors which were painted a dark color, enclosed by a glass-storm door, and facing sunlight.

Wrinkling - wrinkles in the top paint layer may be caused if paint is applied too thickly, if the paint is not brushed out, or if paint is applied over a prior coating which has not dried.

Yellowing - caused by lack of natural light, or alternatively by exposure to sunlight. Moisture, heat, or fumes (such as from oil or gas fired equipment) can also cause yellowing of some paints, as can some paint additives (such as "mildewcides").

PAINT FAILURE INVESTIGATOR - Microscopic Examination of Paint Chips as a Paint Failure Diagnostic Aid

Photos and text at this document are from detailed paint failure studies conducted by our field and laboratory paint failure investigation service, including site photographs, lab photographs through the forensic microscope, and paint chip samples are available as a class for building inspectors. Simple 10x or stereo-microscope-magnified "forensic observation" of a surface from which paint has peeled, observation of the back of a paint chip, and dissection of a paint chip or painted surface to disclose the history of the layers of paint applied to a building is important in forming an opinion about the reasons for paint failure on a particular building. For completeness, such observations should be combined with a record of detailed site observations and a report of historic conditions at the building in order to document probable causes of or contributors to the failure of a painted surface.

Here are a few paint chip and paint dust photos from our forensic microscopy lab, along with some diagnostic comments

• Wood fibers on the back of this paint chip confirm that the paint didn't want to "let go" of the surface to which it was applied. I believe that this paint was probably "pushed" off of the surface by moisture, perhaps also frost as this investigation was on a building in a northern climate.

• Chalking paint on the under-side of a paint chip is shown in this high power microscope photograph. The very fine particles may be less than one micron. Finding this dust on the back of a paint chip taken from a failing surface is a strong suggestion that the failing paint was applied over a chalked surface. This failure may have been avoidable by better surface cleaning, perhaps power washing, and possibly by a better choice of a primer. The pine pollen grain in this photo is included for scale.

• Paint pigment as a typical particle is much larger than the chalking particles shown above.

• Paint droplets left by spraying paint, such as this fungicidal sealant (MicroBan(TM)) in the microscope are entirely different from pigment fragments collected from a painted surface or failing paint chip - see the preceding photograph. Paint droplets look black in the microscope by normal transmitted light, but if a simple forensic technique is used to provide top lighting you'll see the actual color of the paint pigment as shown in this photo.

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Continue to the next section of this document at PAINT LAB SAMPLE PREP "A Procedure for Preparing Paint Samples for Examination by Reflected Light Microscopy, and Simple Chemical Tests to Identify Acrylic and Alkyd Paints" or use the links at page left to navigate the document and our website.

PAINT REFERENCES - Paint Failure Diagnosis, Forensic Analysis of Paints, Moisture Control in Buildings - References For Avoiding, Diagnosing, and Correcting or Curing Paint Failures

• Paint and Surface Coatings, Theory and Practice, R. Lambourne & T.A. Strivens, Ed., Woodhead Publishing Ltd., William Andrew Publishing, 1999 ISBN 1-85573-348 X & 1-884207-73-1 [This is perhaps the leading reference on modern paints and coatings, but is a difficult text to obtain, and is a bit short on field investigation methods - DF]
• Analysis of Modern Paints, Thomas J.S. Learner, Research in Conservation, 2004 ISBN 0-89236-779-2 [Chemistry of modern paints, overview of analytical methods, pyrolysis-gas chromatography signatures of basic modern paints and their constituents, Fourier transform infrared spectroscopy for paint analysis, direct temperature-resolved mas spectrometry, and analysis in practice - technical reference useful for forensic paint science, focused on art works -DF]
• Seeing Through Paintings, Physical Examination in Art Historical Studies, Andrea Kirsh, Rustin S. Levenson, Materials in Fine Arts, 2000 ISBN 99-051835 [ forensic science, technical reference, focused on art works - DF]
• Paint Handbook: testing, selection, application, troubleshooting, surface preparation, etc., Guy E. Weismantel, Ed., McGraw Hill Book Company, 1981 [Excellent but a bit obsolete paint theory and practice, also a bit light on field investigation methods, out of print, available used-DF]
• Art, Biology, and Conservation: Biodeterioration in Works of Art, RObert J. Koestler et als. Eds., Metropolitan Museum of Art, 2003, ISBN 1-58839-107-8
• Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF]
• Understanding Ventilation, John Bower, The Healthy House Institute, ISBN 0-9637156-5-8, 1995 [General building science-DF]
• Dampness in Buildings, Diagnosis, Treatment, Instruments, T.A. Oxley & E.G. Gobert, ISBN 0-408-01463-6, Butterworths, 1983-1987 [General building science-DF]
• "Moisture Control in Buildings: Putting Building Science in Green Building," Alex Wilson, Environmental Building News, Vol. 12. No. 5. [Good tutorial, "Moisture 101" outlining the physics of moisture movement in buildings and a good but incomplete list of general suggestions for moisture control - inadequate attention given to exterior conditions such as roof and surface drainage defects which are among the most-common sources of building moisture and water entry.--DJF]
• "Paint Failure Problems and Their Cure," Daniel L. Cassens and William C. Feist, National Forest Products Laboratory, online via Purdue University, http://www.ces.purdue.edu/extmedia/NCR/NCR-133.html
• "Why House Paint Fails," Mark Knaebe, US FPL, http://www.fpl.fs.fed.us/documnts/finlines/knaeb95a.pdf
• "Why Paint Jobs Fail," http://www.bennette.com/pdf/whyfail.pdf
• "Supplemental Guidelines for Removing Paint From Interior and Exterior Wood Surfaces," US General Services Administration, http://w3.gsa.gov/web/p/Hptp.nsf/0/40aff5a115b6a9e5852565c50054b4f4?OpenDocument
• "Common Paint Problems," http://www.parkerpaint.com/Common%20Paint%20Problems.html illustrates common paint failures - though their images and text appear to have been stolen from PPG - see http://www.ppg.com/getpaint/etraining/solver/exterior.html which catalogs paint failures and causes
• "Paint problem solver" from Lowes, http://www.lowes.com/lowes/lkn?action=howTo&p=Improve/PntPrbSlv.html&rn=RightNavFiles/no.html
• "Mill Glaze: Myth or Reality," � R. Sam Williams, Mark Knaebe, US FPL, http://www.fpl.fs.fed.us/documnts/finlines/willi01a.pdf
• http://www.paintlab.com/failure.html is a lab offering paint chip failure analysis

• PPG Exterior Failures http://www.ppg.com/getpaint/etraining/solver/exterior.html

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• Quotes in the opening text of this document are from the encyclopedic but not quite complete paint website: PPG Exterior Failures http://www.ppg.com/getpaint/etraining/solver/exterior.html