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Microscopic Lab Analysis & Photographs of Paint Failures on Building Surfaces Diagnose Causes InspectAPedia®  -     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

Here we provide paint analysis lab photographs of types of paint 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. Readers can see additional paint test lab photographs at Paint Failure Case Photographs-LAB

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

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 accompaning 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

• 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.

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.

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.

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.

Distinguishing solvent blisters from small moisture blisters:

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 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 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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PAINT & STAIN GUIDE, EXTERIOR
PAINT FALURE, DIAGNOSIS, CURE, PREVENTION
PAINT FAILURE CHECKLIST
  EXTERIOR CLUES
  INTERIOR CLUES
  SITE HISTORY
  PAINT FAILURE INDICATORS
COMMON PAINTING MISTAKES
  BAD SURFACE PREP
  PAINTING SHORTCUT ERRORS
  PAINT OVER MOISTURE
  INCOMPATIBLE PAINTS
  PAINT in SUN or WIND
  PAINT on STUCCCO, FAILURES
PAINT FAILURE DICTIONARY
PAINT FAILURE ANALYSIS LAB PHOTOS
Paint Failure Case Photographs-SITE
Paint Failure Case Photographs-LAB
PAINT LAB SAMPLE PREPARATION

PAINT REFERENCES

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 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 mass 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.htm

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More Information on Building Diagnostic Inspections and Repairs

• Exteriors, Landscaping, & Siding - Inspection, Repairs, Product Failures

• 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

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