Overlays & Sealers

This category answers two different questions. What do I do about a slab that looks bad, and what do I put on a slab that looks good.

Overlays answer the first. An overlay is a cementitious layer applied over existing concrete to give it a new surface, and it exists because tearing out and repouring a slab is expensive. Thin overlays skim the surface for cosmetic renewal. Traffic rated overlays are formulated for driveways and areas that carry vehicles. Decorative overlays are built to be stamped, textured or colored. What all of them share is that they are only as good as their bond to the slab underneath. Overlays go over structurally sound concrete that has been mechanically prepared and cleaned, and they will not fix a slab that is failing structurally or one that is still moving.

Sealers answer the second, and the split that matters is penetrating versus topical. A penetrating sealer soaks into the concrete and reacts or lodges below the surface, protecting against water and salt intrusion while leaving the slab looking essentially unchanged and leaving the surface breathable. Because there is no film on top, there is nothing to peel, which is what makes penetrating sealers the sensible choice for exterior flatwork in freeze and thaw climates. A topical sealer forms a film on the surface. That film gives you gloss, color enhancement and stain resistance, and it is what people mean when they want a wet look driveway or a sheen on a polished interior floor. The cost is that a film can wear, can peel if it was applied over a damp or dirty slab, and can trap moisture in an exterior slab that needs to breathe.

Sheen is its own decision, and it is where matting agents come in. A matting agent knocks a gloss product down toward satin or matte. Gloss shows more depth and more color, and it also shows every scuff, every scratch and every bit of dust. On a large commercial floor, a lower sheen usually looks better six months in. Stains and dyes sit alongside both, since color goes into the concrete or the overlay before the sealer goes over it. The sequence is preparation, color, then seal, and getting that order wrong means stripping a sealer to fix a color.

The universal rule in this category is preparation and dryness. Overlays need a mechanically prepared, clean, sound substrate. Sealers need a slab that is clean and dry, since sealing moisture into concrete causes blushing, cloudiness and adhesion failure. Test rather than assume, and sample any decorative product on the actual slab before committing the whole job to it.