Sealing Epoxy Terrazzo

Epoxy Terrazzo is typically sealed with a maintenance material like a low solids acrylic or acrylic/urethane blend. These sealers are not designed as a permanent coating, they are applied via mop or lambs wool pads, quite thin and they dry quickly.

Upon occasion, particularly in Healthcare or Pharmaceutical, a more chemical resistant and permanent sealer is required to protect the marble or other aggregate. Urethanes like 4638 or 4685 are good choices but do present a challenge for the installer.

Finishing Terrazzo requires several grind steps. This process opens air pockets trapped within the matrix. These 'pinholes' range in size from 1/8" in diameter to very small. A grout step is part of the finish process to fill these holes. Excess grout is removed in the final polish step. Many of the small holes do not get filled, as the grout resin does not flow into such a small void. It bridges the void and then is ground off in the polish.

Unlike the maintenance sealers, 4638 and 4685 form a much thicker film via traditional application techniques. These resins take hours to cure versus minutes with the sealers. Without precaution you can seal Terrazzo, have it appear perfect but upon return the next day find hundreds of what appear to be 'fish eyes' In the center of each will be a small pinhole. During cure material was blown away from the hole, or was sucked in.

To avoid this from happening on your project you have two choices. First, you can attempt to seal all pinholes with a quick curing grout material such as 4844 PAce-Cote that is applied via spring steel trowel, at a rate of 600-700 feet per gallon. Upon cure, 1.5 - 2 hours, lightly sand to remove any marks, and coat with 4638/4685.

The second approach is to apply the 4638/4685 via spring steel trowel or squeegee at a rate of 800 + feet per gallon and back roll with a high quality 3/16" nap cover. At this coverage rate the film is so thin you do not see height difference around the 'pinholes'. You cannot apply these materials at this coverage rate unless you are on your knees.