Photo of paint solvent blistering, edge view in laboratory Microscopic Lab Analysis & Photographs of Paint Failures on Building Surfaces Diagnose Causes

  • PAINT FAILURE LAB ANALYSIS - CONTENTS: Paint Analysis Lab Photos of Types of Paint Failures. How to diagnose the cause of failing paint on a building exterior or interior. Paint failure diagnosis checklists for the building exterior & interior.
  • POST a QUESTION or READ FAQs about what paint failures look like in the forensic lab

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Laboratory analysis of paint samples to diagnose paint failure cause:

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

Photograph of  paint chip-- 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.

[Click to enlarge any image]

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.

Above and in photos below 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 whown above 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.

Photograph of  paint chalking

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.

Photograph of  paint pigment

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

Photograph of  paint droplet

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.

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.

Photograph of  peeling paint on a building exterior - can you diagnose this paint alligatoring failure by eye?

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 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.

Photo of paint solvent blistering, edge view in laboratory

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.

Photo of paint solvent blistering Photo of paint solvent blistering

Photo of paint solvent blistering, edge view in laboratory

Paint 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:

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.

Photo of paint resin failure, viewed by microscope in our paint laboratory

These details become more apparent in the laboratory under forensic microscopic examination of samples of failing paint.

Paint 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.

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.

Photo of paint failure due to inappropriate use of skim coat with crack filler Photo of paint failure due to inappropriate use of skim coat with crack filler

Photo of paint failure due to inappropriate use of skim coat with crack filler

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 these photos.

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 and also which cites tannin staining, when tannic acid, such as oils in pine knots or cedar bleed through new paint.

Also see Rusting above.

Photograph of surfactant leaching failure of a painted exterior wallSurfactant 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.

Paint Failure Analysis Lab Articles


Continue reading at PAINT FAILURE CHEMICAL TESTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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