Elastomeric was designed for industrial buildings that were leaking. About 18 years ago it made it’s way into the residential market for stucco houses and buildings.
Unfortunately there were problems. Part of the problem was that it wasn’t being applied properly. This product needs two coats and total thickness varies between products but it is comparatively thicker than almost all other products.
Many companies were thinning it down to allow for easier application for brush and roller and most sprayers weren’t capable of pushing though that thick of product. As a result the properties of the product were compromised and therefore not able to do it’s “job”.
Another problem was this product must have solid coverage, which means no holes. If there are any holes moisture is able to get between the coating and the stucco creating a plastic bag scenario allowing mold and mildew to build. Yes, elastomeric is breathable but its percentage is really low which doesn’t allow moisture to escape easily.
If there is enough moisture behind the coating, as it heats up by the sun, it can expand and literally push the coating off the surface thus resulting in failure. Even if the paint is solid everyday activities by the homeowner can puncture the surface resulting in the same problems.
This product also costs more. A gallon only does about 100 sq feet compared to latex paint or stain, which does about 300 sq feet… something to keep in mind when comparing estimates.
All this having been said, we have used the product for areas that are leaking (please note I said areas… sometimes only one wall needs doing and the rest can be done in a more conventional product) and it is really good when used for what it is designed for. In my opinion I don’t think it is a product that belongs in mainstream painting.