When a concrete floor begins to lose its luster, you can often restore it by polishing it or adding a refresher seal coat. When the finish has worn, though, you're faced with some of the same decisions you would face if the floor were wood: You can just live with it, paint it or cover it with another floor covering. Refinishing is another option, and it's the only option if you want to change the color of the concrete, which involves grinding the surface to remove the existing stain.
Stripping the Finish
If your main concern is touching up the existing stain without changing the color, or you want to add color to unstained concrete, you can use a chemical stripper to remove the existing seal coat. The process is similar to stripping finish from wood:
Apply a coat of concrete and masonry stripper to the entire floor, using a paintbrush, paint roller or airless sprayer. Let it remain on the floor for the time recommended on the container -- usually six to eight hours -- or until the finish begins to noticeably bubble and peel.
Remove the stripper -- and the sealer along with it -- with a scraper or wire brush. Collect the stripper in a bucket and dispose of it as hazardous waste.
Rinse the concrete thoroughly with clear water to remove all the residue. Pour water on the floor from a bucket or wet the floor down with a garden hose and mop with a string mop. Then collect the residue and put it with the stripper residue for disposal.
Grinding Out the Color
If your plans call for a change of color, and you need to remove an existing stain, you'll need to rent a hooded floor grinder. This heavy-duty tool resembles a floor buffer, but instead of a polishing pad, it has three grinding wheels that scrape off the surface coating of sealer and stain. If you choose to grind, you don't need to strip the sealer -- the grinder will remove it.
The procedure involves little more than running the grinder over the floor until the stain has been removed, but that may take days, depending on the floor. Moreover, preparing for grinding can be an involved process.
Because the procedure raises clouds of powdery concrete dust, it's important to seal the room with plastic, including all the air vents. Protective clothing, goggles and a respirator are musts when doing this job.
Cleaning, Etching and Staining
Once you've removed the film coating from the surface and neutralized the color, you're ready to restain. You'll want to clean the floor thoroughly before staining, particularly if the floor didn't have a finish. Once the floor is clean, applying a concrete stain is easy.
Mix a solution of 1/2 to 1 cup of trisodium phosphate per gallon of water, and scrub the floor to remove oils and stains that may have penetrated. Rinse well with clear water.
Mix the acid stain or concrete dye you want to use, according to the instructions on the container, and fill the reservoir of a garden sprayer about three-quarters full. Pump the sprayer to pressurize it.
Wet the floor down with water, and then spray the stain in an even pattern over the entire floor. To get a uniform color distribution, have a helper walk behind you and roll out the stain with a paint roller. If you're interested in getting a mottled finish with an acid stain, you may prefer to let the stain penetrate unevenly -- if so, omit the rolling.
Let the stain dry overnight. Repeat the process with a different color if you're trying to create a a multicolored pattern that resembles natural stone.
Applying an Overlay Finish
The best method for applying a seal coat depends on the product you're using. It may be best to use a brush or roller, but some products are best applied with an HVLP or airless sprayer. You can also trowel or spray on an overlay to provide added texture. If you plan to do this yourself, follow the manufacturer's instructions for the product you're using.
A Word About Painting
Painting your concrete floor is always an option, and it's one that circumvents the need for stripping or grinding. It's important to clean the floor thoroughly with TSP to remove any deposits that could prevent the paint from adhering. You can use virtually any type of paint, as long as you protect it with two coats of polyurethane floor finish.