David H. Nicastro, PE, F.ASTM
Elastomeric wall coatings (EWCs) are an important part of new and remedial construction, protecting cladding from water penetration. Assuming they are properly applied, premature failures of EWCs typically involve their manufacturing formulation—degradation due to inadequate ultraviolet (UV) radiation resistance, or cracking due to inadequate low-temperature crack-bridging ability. The photo below shows a problem caused by formulating, but not by the manufacturer.
Like paint, an EWC serves as a finish as well as a protective coating, so durability should be evaluated on aesthetic performance, as well as sealing ability. The photo depicts a portion of a hotel that was coated with an EWC. Although the coating worked as intended to remedy water infiltration, it faded very quickly to the salmon color at the top. The selected color was tan, as shown being re-applied at the bottom. Some colors are inherently more stable than others, but that could not explain this problem—tan is not a challenging color.
In our failure investigation (with the manufacturer’s assistance), we discovered the local coating supplier made two errors. First, it used the wrong tint base. It is common for coatings to be stocked in a white base by local suppliers, who then tint them to match any color by adding pigments. This manufacturer provides the coating in several bases to be compatible with different pigment combinations, but the supplier did not know the difference between them.
Secondly, the supplier used organic pigments subject to fading, rather than the specified inorganic (mineral) pigments. Again, the supplier did not know the difference. Both types of pigments will match the selected color initially, but some organic pigments fade rapidly in sunlight—less than a year in this case.
Since this EWC was a high-quality product, the remedy simply required applying a new topcoat formulated with the correct tint base and pigments. However, a financial remedy was harder to achieve—the scope and liability of local supply shops are not typically addressed by specifications, contract documents, or project insurance coverage.
Specifiers should discuss with the coating manufacturer the UV stability of particular colors, and how to specify the proper tint base and pigments to achieve a durable finish.
The opinions expressed in Failures are based on the author’s experiences and do not necessarily reflect those of the CSI or The Construction Specifier.
David H. Nicastro, PE, F.ASTM, started the Failures column for The Construction Specifier in January 1994. He is the founder of Building Diagnostics Inc., specializing in the investigation of problems with existing buildings, designing remedies for those problems, and resolving disputes arising from them. He is a licensed professional engineer, and leads the research being performed at Building Diagnostics’ testing center, The Durability Lab, at The University of Texas at Austin. He can be reached by e-mail at email@example.com.