A grout coat is a thin filler spread over concrete during polishing to fill pinholes and small voids. It’s usually an epoxy- or cement-based material worked into the surface by the grinder. Filling those voids gives a cleaner, more uniform finish. Excess material is ground off in the next steps.
Why a Grout Coat Matters for Polished Concrete
Grinding opens up the slab and exposes tiny holes and pits you couldn’t see before. Think of it like filling the grain on an open-pored wood before finishing it. The grout coat packs a filler into those pinholes and micropits, and the crew keeps grinding and polishing over it.
It isn’t just cosmetic. Left open, those voids collect dirt, and grit and traffic can keep cutting into them and make them larger. Filling them gives a tighter surface that’s easier to clean and polishes more evenly.
The grout coat goes on after the coarse-to-medium grinding steps, once the crew can see how many holes the slab has. Not every floor needs one. Some slabs come out tight, and others, especially ones ground deep to show stone, open up a lot of voids. It’s often listed as a separate line item.
Grout Coat FAQ
Can you use grout to fill cracks in concrete?
A grout coat is for tiny pinholes and pits, not real cracks. Larger cracks and joints get a separate repair or filler before or during polishing. Ask your contractor how they’ll handle cracks, since those usually stay visible in a polished floor.
Does every polished concrete floor need a grout coat?
No. It depends on the slab. Floors that open up lots of pinholes during grinding benefit the most, especially for higher sheen levels where small voids are easier to see. Your contractor can tell after the first grinding passes.