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Paint failure & paint problme dictionary: here we provide an illustrated dictionary of types of paint failures and painting terminology. We show what different types of paint falures and painting mistakes look like on buildings and we define the terms used to explain kinds of paint job failures.
This article series reviews common building exterior & interior painting mistakes, describes how to diagnose paint failures on buildings and in art conservation. We outlines a procedure for diagnostic field inspection & lab testing of failed painted surfaces on buildings. 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.
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Since no single reference listed all of the paint failure types, the list which follows is a collection of paint failure types based on ... 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. Other information and paint failure suggestion sources are provided at Technical Reviewers & References.
Paint 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].
Shown at above left is a paint adhesion failuire on a pressed tin metal ceiling following an extensive water leak from above. Details are at METAL CEILINGS ALUMINUM & TIN
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.
Paint adhesion failures or paint cracking on stucco surfaces due to improper application or water exposure - see STUCCO PAINT FAILURES
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.
Paint 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.
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 microphotograph 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.
Also see NCR133 article below.
Distinguishing solvent blisters from small moisture blisters:Paint Solvent blisters occur as the paint is drying as solvent trapped behind the drying or dried outer film of the paint layer form gases (perhaps from sun exposure) which form a bubble and try to escape from the film.
Paint 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 occasion 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.
Paint Blooming - (blushing) - this is moisture getting into varnish, shellac, lacquer. This coating failure leaves a milky opaque (usually-white) cloud on (or actually within) the coated surface. Paint bloom may not wipe off with a fingertip as does most efflorescence - so paint blooming is not the same visual effect as surface efflorescence, though many paint failure analysts use "bloom" for both cases and although the cause might be the same - moisture. See PAINT on STUCCO, FAILURES and see efflorescence below for an example of white bloom of efflorescence on a painted stucco exterior.
Paint 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.
Paint 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.
Paint 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.
For diagnosing hairline cracks in painted stucco, also see STUCCO PAINT FAILURES.
Paint 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.
Paint 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. Efflorescence 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. Efflorescence is hygroscopic, and by attracting more moisture, will continue to accumulate. For some detailed photos of efflorescence (sometimes mistaken for "mold") see Efflorescence & white or brown deposits
Our photo (left) shows white efflorescence and mottling that appeared on a painted exterior new-stucco wall of a home in the Southwestern U.S. after less than a year of application. See PAINT on STUCCO, FAILURES for details of stucco paint problem diagnosis & avoidance.
Painting over open cracks where moisture has not fully evaporated or painting over new too soon and where the stucco surface pH or alkalinity remains too high (over 11) invites cosmetic problems as well as early wear or failure of the painted coating. The application and curing procedure used for stucco, in turn affect the wall pH - it needs to be tested by the painter before the paint job begins. Also see Paint Blooming.
Paint 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.
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.
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.
Paint 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.
Paint 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-named 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.] Mildew is indeed a type of mold, but it grows only on living plants.
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 Paint - 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.
Paint 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.
Paint 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. Rust stains on buildings - see Rust Stains on Shingles
Paint 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.
Paint 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 our paint failure site investigation photos just below.
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.
Paint 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.
Paint - 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.
Paint 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").
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