Question:
What's the best way to touch up minor scratches in the surface of my concrete countertop? Is this something I can do myself, or should I hire a professional?

Answer:
Because the scratches are minor, they are most likely in the countertop sealer and not in the concrete itself. Just like with scratches in a car door, there are two approaches to fixing them. One is to simply touch up the scratch with more sealer, and the other is to reseal the whole slab. For more information, see How to Fix Scratches in Topical Sealers.

Brush shapes (left to right): Spotter, round, and liner.

An ultra-mini spotter brush.

Touching up the finish will restore the protection and reduce the appearance of the scratch. But depending upon the degree of care used and the size, location, and depth of the scratch, the touchup repair might be more visually objectionable than the scratch itself. This is usually something a homeowner can do, but ask your contractor for good instructions and some sealer you can easily use and apply. You don't want to use a two-part sealer that must be mixed and sprayed onto the countertops with special equipment. Your "touchup kit" should be simple, almost like the touchup kit used for cars.

Generally a single-component sealer, such as an acrylic, is used for scratch touchup. A very fine artist's brush and a steady hand are what it takes to apply just the right amount of finish to fill in the scratch. Often the excess sealer that builds up around the scratch is what looks bad. It's best to remove the excess with a paper towel, a dry brush, or a cotton swab while the sealer is still wet.

A "spotter" brush is the ideal type of application tool to use because it's very fine and doesn't hold much sealer. The bristles are short, and the small amount of sealer they hold won't squeeze out. Round brushes have fine points and are the most common type you'll find in arts-and-crafts stores. But round brushes can hold too much material and make it difficult to create a fine line. Liner brushes are often used for pin striping and lettering, where long flowing strokes are needed. They have long bristles and a fine point, but uneven pressure will cause the bristles to flare out, creating a wider line of sealer.

Nail buffing block.

The ultra-mini spotter (shown here) has a very tiny brush. The size 20/0 indicates that it's very small. A size 3/0 is larger, and a 2 is even larger (roughly 2 millimeters in diameter).

Once the touchup is dry, you can then adjust the sheen to match the surrounding finish. If there is excess material in the touchup, first use a razor to carefully scrape off only the excess. It's better, though, to use a little less sealer and not have any excess. Any scratches to the surrounding finish will make the repair more apparent. Blending the repair into the rest of the countertop often involves precise sanding with fine-grade sandpaper. Specialty nail buffing pads for manicures are great tools for carefully buffing, smoothing, and polishing the touchup. Nail files are coarser and good for removing material.

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