Concrete that looks bare may still contain a cure-and-seal product, penetrating treatment or old coating residue. Before applying a new coating, test whether water can actually wet and absorb into the concrete rather than assuming the surface is porous.
The Simple Water-Drop Test
Place small drops or a dime-size bead of water on clean, dry concrete in several locations. If the concrete darkens and absorbs the water readily, the surface is behaving like porous, unsealed concrete. If the water beads and remains on top, a sealer, curing compound, dense finish or contamination may be preventing absorption.
Sherwin-Williams describes a similar absorption check for decorative concrete: if a dime-size bead does not absorb within the expected time, a cure-and-seal product may be present and stripping may be required before recoating. This is a screening test, not a chemical identification of the old material.
Why This Matters Before Etching
Acid etching reacts with mineral concrete. If a sealer is blocking access to the cement paste, the etch may do little or nothing. A common mistake is trying to use acid as though it were a universal sealer stripper.
If Water Beads
- Check records, old containers or contractor paperwork for the prior product.
- Test multiple areas; wear and traffic can make one spot more absorbent than another.
- Follow the new coating manufacturer’s instructions for removal or compatibility testing.
- Use a small adhesion test area if the old treatment cannot be positively identified.