Painting concrete floors
Painting concrete floors is an advanced-level project requiring meticulous preparation.
By Chris Haught
Concrete is one of those unusual and high-risk surfaces that, at some point, most of us consider painting. The most commonly painted concrete is on garage and basement floors. The reasons for painting concrete floors are to improve the look and to make the surface easier to maintain and keep clean. But painting concrete floors is not for beginners.
Before painting concrete floors, make sure the surface generally remains dry year round. If there are problems with water or even excess moisture in the area, painting may not be a good idea.
If the concrete is new, be sure it’s fully cured before painting. The required cure time will be based upon the type of mix used when the concrete was poured.
Prepping concrete floors for paint
The first step in painting concrete floors is to make sure the concrete is absolutely clean; sweep and vacuum it thoroughly. Then you’re ready to prepare the concrete for paint. This can be done effectively in two ways: mechanically or chemically.
Mechanical prep requires the use of an upright sander or grinder using very low grit, aggressive abrasives or even a diamond wheel attachment to rough up the concrete surface. This is hard work and can be dusty. You’ll need ear protection and a cartridge respirator rated for dust.
Chemical preparation, also referred to as an acid bath, is physically easier to do. But, it also comes with its own risks. The traditional chemical used for concrete prep is muriatic acid, one of the most dangerous chemicals you can purchase for home use. It’s a reactive chemical, meaning it can damage almost anything it touches. That’s what makes it so effective as a concrete and masonry cleaner. Muriatic acid penetrates the concrete surface and kicks out any mineral deposits or chemical imbalance present, leaving an etched surface.
Synthetic substitutes for muriatic acid are available and are packaged as concrete cleaners. Although they are synthetic, they require the same safety procedures. Whichever chemical you use, it’s critical that you wear a cartridge respirator, cover all skin, and be sure not to splash the chemical.
The chemical is mixed with water (look for mixing ratios on the container), using either a 5-gallon bucket or a garden-style pump sprayer. Add the acid to the water already in your bucket, and not vice versa, to avoid splashing.
Carefully spread the chemical on the area using a mop. You’ll see that the mix “fizzes” on the concrete, as if you had spilled soda. That’s normal.
It’s best to treat the area in sections, so that you can keep it wet. Ideally, the prep is done with two people. One person applies the chemical, and the second person rinses the treated sections thoroughly with water from a garden hose.
If the acid begins to dry before it can be rinsed, a powdery residue forms on the surface that requires more rinsing. Once the entire floor has been treated with the acid, do a full final rinse and use a push broom to move any standing water out of the area.
Allow the concrete to dry for at least 48 hours with no traffic before proceeding. Floor fans and heat can be used to stimulate drying.
If you aren’t able to commit to this level of surface preparation, don’t paint the concrete. A failed coating on concrete due to incorrect prep is difficult, inconvenient and costly to remedy.
When you’re ready to paint, you’ll need an 18-inch roller frame, cover and tray; a 2½-inch cutting brush and a 6-inch mini roller setup. It’s pretty much a cut-and-roll operation. Brush cut the perimeter, use the mini roller to widen the cut, and then roll out the main body of the concrete using the large roller.
Several good options are available for concrete finishes. For basement floors, where foot traffic and general wear and tear are the biggest challenges, you can use a solid acrylic concrete stain. These stains can be mixed to nearly any color you want. They are easy to apply, have a relatively low odor and are durable.
For garage floors, where vehicles will be on the surface, it’s best to use an industrial grade, two-part epoxy system. These come in kits that include a base and a hardener, usually mixed prior to application. Epoxies are a bit thicker and slower to apply, and they have a significantly higher odor level, both during application and dry/cure times.
Whichever product type you choose, be sure to follow the manufacturer’s instructions regarding how much time you should allow the concrete to cure before using it.
Disposing of muriatic acid
If any muriatic acid remains after the prep, dispose of it. It’s too dangerous to keep around.
Do not, however, pour it down a storm drain, sink or toilet, or place a closed container of muriatic acid in the trash. To dispose of it, try recycling. Many cities provide areas for recycling hazardous chemicals. Call your local recycling center for more information.
If recycling is not possible, use garden lime to neutralize the muriatic acid. In a large bucket, pour three or four cups of lime and add a gallon of water. Stir it with a scrap of wood that you can later discard. Now, slowly add the acid to the bucket. Keep your face turned away while pouring and wear the personal protective equipment (PPE) you wore during the application. Stir until all chemical “fizzing” has stopped and the muriatic acid is neutralized. It may be necessary to add more lime. The fully neutralized acid can now be safely poured down a sink or storm drain.