Elastomeric Coatings: Can they be too thick?

Most elastomeric coatings function better when they are thicker. Each additional coat adds mil thickness and unlike other coatings especially asphaltic products which become brittle when they are thick, the added dry film thickness (DFT) enhances properties of elongation and tensile strength.

Imagine a very thick rubber band versus a thin rubber band. Which one do you think will last longer?

If our only concern was tensile strength and elongation,  then we should lay down as thick a coating system as our budget would allow. However, elastomeric coatings also bring other properties to the table.

In wall coatings, permeability or breathability is an important property not to forget.

Elastomeric wall coatings like Acrymax AF135 are designed to breath. So while keeping the building waterproof to rain and other moisture,  elastomeric coatings allow for the natural breathing of masonry surfaces without affecting the adhesion of the coating.

However each additional coat applied to the surface reduces the breathability of the coating system. Eventually the water vapor that used to move freely out of the masonry will now gather behind the coating and condense into liquid water. This water will lead to delamination of the coating (no matter how well the base layer is adhered) and the formation of a blister. Eventually this blister will rupture and cause a major coating defect.

So while this is not the norm with elastomeric coatings (they are typically applied too thin), this phenomenon is still something that needs to be kept in mind when working with and specifying elastomeric wall coatings.

Keep in mind, with roof coatings you generally want a less breathable surface and too much thickness is much less concerning.