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The Whys and the Why Nots for Elastomeric Coatings

It is summertime and folks are looking to renew and waterproof their buildings. Elastomeric paint is the ‘to go‘ method and sometimes hyped for coating.

A little background about elastomeric. I remember in the 1960’s a Florida manufacturer first sold the product to protect house trailers which have very active joints. It sold across the country, until major paint manufacturers took it up. Basically, it is a coating when applied much thicker than standard paints. The method of making it includes a chain of molecules not fully cured, allowing it to expand and contract. Early versions had problems of lumpy surfaces and dirt and stain gathering.

These have been mostly solved, with the exception of silicone coatings, which also unfortunately still gather dirt, while being the most durable.

The most common use is on masonry surfaces and low slope roofs. We have used it to great success for over 30 years.

Caveat: the work like most coatings is incumbent on proper application and preparation.

The surfaces to be coated must be dirt and chalk free.
These surfaces should be limited to masonry and low slope roofs.
Priming is an absolute necessity, otherwise
‘pin holing’ in the coating will appear in the finish coats of elastomeric. This is almost impossible to fix. Wind driven rain will blow into the pin holes. The building will leak, even with elastomeric coatings in high wind areas.
All cracks and joints to dissimilar materials, such as windows, doors and light fixtures must be caulked with a modern caulk (e.g. not latex or urethane). If left open, water will enter and not come out.
For waterproofing the individual manufacturer’s mill thickness must be followed. If followed warranties are available.
Typically 2 coats are applied over a primer. A single coat if no big waterproofing needs are present is still much more durable than latex exterior paint. Why? Hairlines cracks let in water. When the wall heats up in the sun, the vapor pressure inside will ‘blow’ open at the cracks, and eventually paint will peel. Basic physics, the laws of gravity and thermodynamics are not in the mind set of painters. Always verify the mil thickness of the paint, preparation and caulking. Do not buy vinyl or other cheap versions. Always use acrylics.
Otherwise the system may cause more problems with trapped water behind the paint. It does not breathe well, so keep water out.