Ultraviolet (UV) rays destroy elastomeric coating because it’s basically liquid rubber. Liquid rubber oxidizes under UV rays which makes it brittle. The rubber loses its flexibility and the paint becomes flat. When the paint becomes flat the water penetrates the surface and builds up little balloons.
Over time, the water balloons get bigger and cause bubbling and cracking. Once they burst, it causes the paint to shatter from the inside out. If left alone it can cause enough water damage to demand a complete re-stucco.
“If this happens, then why do, or did, painters use it at all? Seems like they should’ve used the best paint for home exteriors,” David asks.
There was a period of time where builders specified elastomeric coating on homes here in Arizona. Specifically, Santa Fe style homes.
Proper painting with this involves a full coat of primer and two coats of elastomeric paint. This should extend the life of the stucco. Unfortunately, no primer and only 2 thin coats of paint were used on almost every job.