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This article reviews common building exterior & interior painting mistakes when painting on modern stucco building exteriors, describes how to diagnose paint failures on buildings, and outlines a procedure for diagnostic field inspection & lab testing 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. Readers should also see Paint Failure Case Photographs-SITE and then Paint Failure Case Photographs-LAB. and see PAINT & STAIN GUIDE, EXTERIOR for a guide to the selection and proper application of paints and stains on exterior wood surfaces.

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.

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STUCCO WALL PAINT FAILURE INDICATORS - Paint Failure Indicators Help Diagnose Paint Problems on Stucco

The combination of cost and schedule pressures and lack of information about the cause of stucco paint job failures may lead some painting contractors into trouble, especially at new construction sites.

The combination of high lime stucco, schedule and cost pressures, and failure to appreciate the importance of stucco hydration and curing prior to painting lead to stucco cracks, white blooms of efflorescence salts in some areas of the stuccoed surface, and early paint job failure - sometimes in less than a year after painting.

Typical causes of or contributors to paint failure on stucco exteriors and other information that we consider when diagnosing paint failure on stucco include the following paint failure causes and signs

• Painting over un-sound stucco or on even a brand new stucco wall that has not been properly prepared and cured. See our photo of antique stucco on an adobe home wall just above.
• Stucco cracking that maps most color changes and efflorescence found together on a building often indicate insufficient hydration during stucco curing and failure to seal the cracks with an elastomeric stucco patch compound prior to painting.
• Failure to sufficiently hydrate the stucco during curing, especially in hot windy climates. Hydration, wetting down the stucco extracts the high levels of lime that are often present to provide workability of the stucco coating during application on the building.
• Rushing the paint job: because the contractor may want to use the scaffolding that was set up to apply the stucco, the painting contractor may be tempted to paint before the stucco was adequately cured.
• Surface conditions at time of painting - cure of the stucco, pH, cracks, moisture level, temperature, wind, sun exposure, even dirt or dust
• Method of application of paint coatings on stucco, spray or roll-on of the paint for primer and top coat, including also the number of coats applied.
• Paint selection for use on stucco: compatibility between primer and top coat, compatibility with new stucco, whether a primer was really applied, whether the paint was thinned excessively or was otherwise defective or even intended for this application. The paint product(s) that have been used should have been selected and applied according to their manufacturer-recommended application methods
• Paint company and paint industry standards and recommendations for painting over stucco need to be respected
• Stucco wall moisture level and stucco wall pH measurements made by the painter during the painting process - were they made at all and were they made properly?
• History of the paint job, the dates of stucco application, date of painting, weather conditions may indicate a rush job or special rain, sun, wind, or freezing exposure weather problems that ruined the paint job before it had a chance to dry and cure.
• Comments by other onsite investigators and their reports, if any, can provide important diagnostic details
• Proposals for remediation/repair re-painting work necessary at the property, if any, can also provide important diagnostic details

Stucco pH as Contributor to Paint Failure

When painting on stucco, the pH (alkalinity) of the surface as well as moisture trapped under paint have been associated with efflorescence or white blooming problems.

White powdery blotches appearing in the painted stucco surface are usually blooms of efflorescence caused by painting over cracks or other areas of extra moisture absorption in the stucco surface. Where recently-applied stucco was not adequately cured, and where surface alkalinity remained too high (pH over 11) white efflorescence blooms are particularly common.  This painting error, sometimes the fault of rushing the paint job, leads to both cosmetic defects and early paint failure.  

While a painter reports having taken some pH measurements with acceptable results, our field work has consistently found that both moisture and pH vary significantly over a building surface. When relying on measurements (and thus rushing the paint job schedule or painting “early”) rather than allowing more elapsed time in deciding when to paint a building, a common error is to rely on “safe” readings obtained in some areas while failing to measure or attend unacceptable moisture or  pH level readings in other building areas.

If on a building the stucco was applied in very hot dry conditions (no surprise in Arizona, for example) and was if the stucco inadequately wet down (hydrated) during cure, that could also have left areas of high pH, making the pH measurements we cited above critical when deciding when to paint or whether additional surface preparation was needed. 

See the stucco painting advice articles we cite at References below.

Efflorescence on building surfaces, including on a painted stucco surface is described at Efflorescence & white or brown deposits.

Water & Weather Impact on Inspection of Painted Stucco Surfaces

As our photos just below demonstrate, the appearance of any painted surface, particularly new stucco, can be significantly different when it is wet.

While there is nothing abnormal or "wrong" with a painted surface that looks a bit different when wet, say darker in color, streaks or the appearance of mottled efflorescence or white blooms on a wall after wetting may be telltales of a paint problem, and certainly these inconsistencies mean that a paint failure investigator needs to inspect when the surface is dry. Inspecting in the rain or just after raining or other sources of wet on a building exterior may lead to incorrect conclusions.

Tips for Avoiding Paint Failure on New Stucco Exteriors

• Hydrate the stucco: Be sure that the stucco is adequately hydrated during curing. Washing down the stucco in hot dry climates and keeping it hydrated avoids cracking and the development of white efflorescence blooms on the building surface. Typically in hot or windy conditions the new stucco is hydrated by the stucco contractor for two or three days to slow the stucco curing rate and to permit the chemistry of stucco curing to complete to a sufficiently hard and impermeable surface.
• Be sure that the stucco has adequately cured before painting. Typically the stucco must cure for at least ten days to two weeks before it can be painted. The pH of cured stucco is normally below 11. If the stucco is still "hot" - not cured - painting it risks early paint failure.
• Fill cracks and holes found in new stucco using an elastomeric stucco patch compound before painting, and be sure that the patches have also cured according to the manufacturer's recommendations.
• Make proper moisture & pH measurements of the stucco before painting. High pH (over 11) stucco is likely to give a problem for the new paint job. When measuring pH on a wall, don't just measure the obviously "ok" areas, measure where you see fine cracking, early signs of efflorescence, areas of paint failure in a primer coat, and in representative sun-exposed and shady wall areas. Different exposures of a building's stucco exterior may cure at different rates because of variations in sunlight and wind. Follow the pH and moisture test and level recommendations of the paint manufacturer.
• Use a water based masonry primer or sealer as the first paint coat. This helps avoid trapping moisture in the new stucco wall. Be sure that the paint is one that the manufacturer recommends for this application, and that it is applied at the thickness (rate of coverage) recommended by the manufacturer. Don't over-thin the paint in the can nor on the surface.
• Be sure that the primer coat is thoroughly dry before applying a second coat.
• Roll-in or brush paint coatings on difficult building surfaces. Relying on spray-alone on building surfaces may do a great job of getting the paint onto the surface quickly (economically) but on some surfaces the paint needs to be worked into the surface with a brush or roller to coat across hairline cracks or to bond well.
• Top coat paint on stucco should be a high quality 100% acrylic latex paint that resists alkaline surface chemistry and the formation of efflorescent blooms or white blotches. Some paint manufacturers recommend two top coats as well as one primer coat on new stucco exteriors. Some paint failures we have investigated were due in part to poor quality or choice of incompatible paints themselves. Don't use bright colors that are non-durable and that will fade quickly in strong sun exposure.
• Apply the paint in thickness recommended by the manufacturer. Use a wet paint gauge if necessary to obtain the proper coverage. One of our assistants at a paint job tried to save money by too-thin application of the paint - a step that cost us extra because we had to paint the entire surface an extra time. Adequately thick coating of paint combined with proper working of the paint onto and into the surface will seal pinholes and hairline cracks in the stucco coating, thus avoiding wind-blown rain leaks into the wall and early paint failures.

A Typical Proposal for Correcting & Re-Painting an Improperly Painted New Stucco Surface Includes

• Trenching around the building walls to permit painting down to ground level
• Pressure-washing the building exterior surface, followed by adequate dryout time
• Patch and seal all stucco cracks using a recommended elastomeric patch compound; caulk at openings and penetrations where the caulk is not in sound condition
• Spray and back-roll or brush-on a water based or more likely in a retrofit repair job, a 100% acrylic primer recommended for use on stucco walls
• Spray and if necessary roll or brush in a top coat of 100% acrylic satin paint recommended for use on stucco walls
• Inspect each painted layer for compliance with the manufacturer's recommended wet-thickness during application
• A warranty on the finished surface (5 years on paint, 20 years on stucco are common)

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PAINT & STAIN GUIDE, EXTERIOR
PAINT FALURE, DIAGNOSIS, CURE, PREVENTION
PAINT FAILURE CHECKLIST
  EXTERIOR CLUES
  INTERIOR CLUES
  SITE HISTORY
  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
    Stucco Paint Failure Indicators
    Stucco pH & Stucco Paint Failure
    Water & Weather & Painted Stucco
    Avoiding Paint Failure on New Stucco
PAINT FAILURE DICTIONARY
PAINT FAILURE ANALYSIS LAB PHOTOS
Paint Failure Case Photographs-SITE
Paint Failure Case Photographs-LAB
PAINT LAB SAMPLE PREPARATION
PAINT REFERENCES

• Painting New Stucco - Combating the Problems, at Scott Paint, a Florida company discusses stucco efflorescence cause and prevention
• Painting Contractor Newsletter on Alkalinity and Efflorescence in New Stucco, The Paint Quality Institute, in which the authors point out that high pH and efflorescence correlate. This article suggests that the painter should use a water-based primer/sealer, (Scott Paint recommends an acrylic stucco primer) then use an alkaline resistant 100% acrylic latex top coat, avoid bright colors, and apply two top coats to be sure that cracks and pinholes are sealed. The Paint Quality Institute is at PO Box 904, Spring House PA 19477. www.paintquality.com
• 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.html

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• 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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