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Here we the details of of paint analysis lab photographs of types of paint failures - what do paint samples look like under the microscope: a library of microscopic evidence of different sorts of paint job mistakes, problems, and failures. This article series reviews common building exterior & interior painting mistakes, describes how to diagnose paint failures on buildings, and outlines a procedure for diagnostic field inspection & lab testing of failed painted surfaces.
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PAINT FAILURE INVESTIGATOR'S PHOTOS- Microscopic Examination of Paint Chips as a Paint Failure Diagnostic Aid
-- Daniel Friedman
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. The accompanying photographs taken in our forensic lab provide examples of paint contaminants or other conditions associated with paint failures that can be of assistance to analysts investigating paints on buildings, artifacts, and works of art.
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
Paint Test Laboratory Listings Welcome: independent forensic and microscopic or chemistry labs offering paint analysis or paint failure services are welcome to be listed here at no fee.
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.
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 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 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. You can see layers of paint quite easily in our page top photograph of a cross-section sample of a painted surface. Measurement of the thickness of paint layers by microscopy is quick and reliable provided that the lab has properly calibrated their measurement reticule and measurement methods first using a stage micrometer.
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