How to stop pin holes, fish eyes and bubbles in epoxy coatings?

Out-gassing from a concrete surface is a result of temperature increases causing air and moisture vapor to be emitted from the slab. Concrete by nature is porous, full of tiny holes. Air and vapor are released when temperatures rise and are absorbed when temperatures drop. Bubbles or Pin-holes in epoxy coatings are caused due to improper priming or rapid drying of the surface of the coating.

Coatings provide a cap, restricting release of air and vapor, but can present a problem during application.

Curing Out gassing with Concrete Coatings in Denver Colorado by Fishers Concrete

The project featured here is a 2,400 sf floor in a Colorado barn. The requirement for the flooring was a high performance epoxy using our Endura E21, Self Priming, 100% solids epoxy.

The process started with mechanically grinding the surface to open up the pores , level the floor and remove any potential bond breakers in the surface. After grinding, the surface was mopped and cleaned, then bubbles were observed as a result of out-gassing from the slab.

As you can see in the photos attached, after the epoxy primer was applied, tiny air bubbles formed. The solution was to lightly sand the floor and reapply a second , high build coating. It seems like a simple solution, but could have been a serious problem if Fishers Concrete did not have experience dealing with out gassing and did not have the appropriate equipment for proper sanding. Let’s not overlook the importance of being prepared, by having enough product on hand for additional coatings should a problem arise.

Out gassing and the results in floor coatings can cause a significant scare when applying. There is no way to anticipate the level of out-gassing in a slab until application. The remedy, like in this case, is experience, proper equipment, problem solving skills and enough product. If the concrete substrate is really porous, you may have to apply two coats of primer, Perdure E02.

Fish eyes are caused when the surface tension of the coatings do not match. This can be avoided by thorough sanding before applying the top coat.

In this project a final Polyurethane top coat providing abrasion and chemical resistance with UV protection was applied.

Project Summary

Location – Denver, Colorado 

Size – 2,400 sf

Concrete Coatings – Endura E21 and Perdure U50

Duraamen Industrial and Polished Concrete Flooring Products are designed to provide labor saving and long lasting flooring solutions. Talk to an expert about your flooring challenges…Please Call + 1 973 230 1301 / eMail Us