Is Epoxy Flooring Waterproof?

Yes. Cured epoxy is impermeable, so a correctly installed floor holds water on the surface instead of letting it through. How the system is built up depends on the slab and on whether the area is inside or outside — that detail is the whole question when the floor has to serve as a waterproof layer. One point matters more than any other: to stop water properly you need a coating system laid to a specified thickness, not a thin coat of epoxy paint brushed over the surface.

Because the material is spray-applied at an even rate, no part of the area is left uncoated — and an unbroken film is what keeps water from getting underneath it.