The Concrete Network
Question:

We tried using acetone to clean up a small area of water-based acrylic sealer that remained white after application to a stained overlay. The acetone removed all the sealer, but also took up the stain and some of the overlay. Why did the sealer remain white, and how do we fix the spot quickly, since the building owner wants to open tomorrow?

Site
Chris Sullivan
,

Brush on a mixture of acrylic tint and sealer to touch up small blemishes
on stained surfaces.

Answer:

The sealer was applied too heavily in this small area, which is why it didn't cure completely and turn clear. Usually, treating these white spots with a solvent will remove them quickly and easily. But in this case, the applicator was a bit too aggressive with the acetone and rag and ended up exposing the underlying white overlay.

If time permitted, you could reapply stain to the affected area to see if the color would take. But since time is an issue, and there's no guarantee that the affected area will take the stain, you need a quicker fix. A simple method for disguising blemishes or off-color areas on stained concrete is to use an acrylic universal tint concentrate or paint. Although you can apply the tint directly to the substrate, the most common method is to blend various colors of tint into the sealer being used on the project until you obtain a close match with the stain color. Then simply brush or rub the tinted sealer onto the surface to cover the blemish (see photo).

Some manufacturers of decorative concrete products offer tint concentrates in an array of standard colors to minimize the need for time-consuming onsite color matching and blending. In most cases, a perfect color match is not required, since a stained floor is expected to have a marbled appearance. The color only needs to be close enough to mask the blemish.

A final note: Make sure the tint is compatible with the sealer you're using. Mix only solvent-based tints with solvent-based sealers and water-based tints with water-based sealers.

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