Yesterday Bill & Kevin Burnett wrote a post for the San Francisco Chronicle that addresses What to check when paint won’t stick to stucco. We figured we would add our two cents.

Photo Credit: Reena Bammi

Elastomeric coatings were developed in the 1950s to answer the problems of paint cracking and peeling on masonry substrates; concrete, concrete block, cinderblock and stucco. Most substrate materials, particularly masonry, will contract and expand when exposed to heat, weather, moisture in the form of humidity and other climatic conditions. Elastomeric coatings are formulated to handle the expansion and contraction without cracking, often lasting for years longer than regular house paints.

Preparation is the Key to Success

The key to a successful elastomeric coatings project is (to paraphrase the Real Estate industry); preparation, preparation, preparation. The substrate to be coated must be properly prepared to receive the elastomeric coating.

• The surface must be cured and have a pH of 9 or less
• The surface must be free of any mold-release agents, dirt, grease or other contaminants
• Cracks and surface irregularities should be filled with an appropriate caulk or sealant and a surface conditioner (basecoat/block-filler) applied to the entire substrate
• Temperature should be between 45 and 100 degrees F
• There should be no rain or freezes forecast for 48 hours following the coating

When the conditions are appropriate and the preparation completed, the first coating of the elastomeric may be sprayed or rolled onto the substrate. After a sufficient cure-time, the second coating may be applied. For previously coated surfaces where an elastomeric coating was used, only one coating of a new elastomeric may be required for weather proof protection, but this should be back-rolled to remove any pinholes.

Potential Problems

Problems of cracking or peeling of finished coatings projects are most often a problem with the substrate, not the elastomeric coating. The most common cause of peeling is moisture migrating from within the substrate to the surface. The water causes bubbling which breaks and peels. The causes of the water may be from leaks within the building, improperly flashed or sealed eaves or roofing, or inadequately caulked or sealed door and window frames. These should be dealt with by eliminating the source of water penetration and the application of elastomeric caulks.

A high pH is also a common cause of peeling on new masonry surfaces. The alkaline salts migrate to the surface loosening the adhesion of the coating resulting in bubbling and peeling. To check the pH of masonry a “pH pencil” is used. The pH pencil is made from a material that reacts to the alkaline by showing a color range based upon the pH level, when in the presence of water. These pencils may be acquired from a number of sources. The surface to be tested should be clean and dry. Spritz the area to be tested with distilled water, then draw a line with the soft pencil. The pencil line will soon take on a color that represents the pH level and is compared to a color graph to obtain the pH measurement. This test is quite accurate and easy to perform.

Local Conditions in Washington, DC, Maryland and Virginia

In the Washington, DC area the weather is subject to extreme changes as influenced by the proximity to the coast, the Chesapeake Bay, the Potomac River and the swampland on which the city was build. The humidity is high as are other negative atmospheric conditions that might affect residential exterior painting projects. Elastomeric coatings are an important element in weather and atmospheric protection in the DC Metro area, often being recommended by professional applicators and coatings technicians, particularly for masonry substrates.