Elastomeric paint is an alternative coating for parts of buildings that need extra protection against adverse weather. Properties include fully waterproofing an external surface, preventing water intrusion through hairline cracks and providing lasting protection for years or even a "lifetime." Elastomeric paints have limitations, however, especially if they are improperly applied.
Elastomeric paints have to be applied five to 10 times thicker than traditional acrylic-based paints, says Bob Cusumano of Coatings Consultants, a member of Painting and Decorating Contractors of America. Creating such a thick film takes longer than applying a standard acrylic paint, and it can result in an unattractive, irregular appearance, which then requires expensive rectification.
If elastomeric paint is not applied thick enough, it can begin to peel off soon after use. Cutting the paint with water to thin it and reduce expense leads to peeling, again because the final application is not thick enough to perform correctly. Coating a surface with elastomeric paint without first applying a primer also causes peeling, because the two surfaces cannot properly bond together.
To achieve a lasting finish with an elastomeric, it's worth pressure-washing the facade of a building before applying the paint. However, this is a time-consuming process that adds cost and requires extra effort. Special equipment needs to be hired for the job, and chemicals, including borax and chlorine, need to be used to remove grease, mildew and dirt. All cracks larger than 1/16 inch must then be filled with a quality acrylic caulk prior to adding the paint. In Michael T. Kubal's "Construction Waterproofing Handbook," the success of using elastomeric paints is described as being dependent on proper substrate preparation, and the book adds that this requires a greater level of knowledge than is needed many typical paint jobs.
Often, severe damage to the surface of buildings penetrates from the back layer of the existing coating, not the very front. Consequently, to achieve a professional result with an elastomeric paint, a primer must be used, but not all primers are suitable. The primer used must be high-quality, be able to resist high levels of alkalinity and be capable of supporting the stress of the cured elastomeric coating film. Choosing a primer can be difficult if there are lots of options, and a primer will increase costs and application time. Even a quality elastomeric paint job with the right primer can "chalk out" after only five or 10 years, according to Scenewright Contracting, resulting in the need to reapply new primer and paint, particularly on stucco.
Elastomeric paints cannot be successfully applied to horizontal surfaces, such as flat roofs and patios, because standing water can more easily penetrate the new coating. They also work better on older buildings and have a higher rate of failure on new structures. This happens because structural cracks and increased alkalinity are factors which diminish as a building ages.