Painting a concrete shop floor
Does the idea of painting a concrete floor leave you cold? Maybe it just sounds like too much work for too little reward. Or perhaps you’ve seen painted floors that have peeled and look bad.
Guess what? A painted floor beats a bare one for several reasons. If you use the right paint (see “Figuring out floor paints,” below) and apply it correctly, your floor will look terrific, clean up easily, and resist wear for many years.
Why does concrete deserve to be coated? It seems impenetrable, but concrete is porous, and happily sucks up liquids and hangs on to small solids. That means spilled stain, motor oil, and sawdust will make themselves at home in the pores. And groundwater from under the slab can seep up, too, creating cold, clammy floors. But paint seals those pores to block out moisture and make it easy to sweep dust and wipe up liquids.
Prepare the surface
Before you start rolling on paint, you’ll need to do an up-front inspection and a bit of prepwork. Why? Because paint simply won’t adhere to a dirty or loose surface. To start, examine the condition of your floor. Is the concrete fresh, old and dingy, or coated with paint? Pick one of the following conditions that describes your floor, and proceed from there.
Freshly poured concrete presents the fewest hassles. First, let it cure for at least four weeks. Then, tape down a 2' square of plastic. Let it sit for 24 hours, and check for moisture underneath. If you find condensation, the floor needs more curing time. If the plastic comes up dry, you can sweep and wash down the floor with mild dete gent, followed by a thorough water rinse. Once the surface dries again, you’re ready to coat it, following the manufacturer’s directions.
Old, dirty concrete
Cleaning oily, stained concrete isn’t exactly fun, but it may not be as tough as you think. Even thick grease stains wash away with the proper cleaner, below. It may take a few applications, but bear in mind that you don’t have to make the concrete look like new. As long as it’s clean, you’re ready for the next step. Use a chemical etching solution (available at paint stores) to give the surface a bit of “tooth.” Once you have etched the floor, wash and rinse it as you would fresh concrete.
A floor that’s been painted before may present the biggest challenge. That’s because the paint you apply won’t be sticking to the concrete, but to the previous paint layer, instead. If that layer is well-bonded, you have no problems. If loose, it’s got to go. Perform a tape test, below, to check the old paint.
Loose paint requires a two-step attack plan: Scrape and then strip. Use a scraper on a long handle to remove as much of the old paint as possible. Remove the rest using a chemical stripper that’s designed to work on concrete, below. Rinse the surface thoroughly to neutralize the stripper, and then treat the surface like old, dirty concrete.
Lay down a new coat
With the prepwork done, painting is easy. Exact procedures vary depending on the product, but a few general rules apply: While you’re cleaning and/or stripping the surface and while painting, make sure you provide adequate ventilation. Fumes from these products can be potent. Walk on the clean floor as little as possible to prevent contaminating the surface. Start painting by brushing a 4"-wide strip around the perimeter. Then paint the main floor, below. Don’t dally as you work. Epoxy paints, especially, have an “open time” of just one or two hours before they lose their workability.
Figuring out floor paints
Before buying concrete paint, make sure you understand what you’re getting. For a shop or garage, stay away from “porch and floor” paints. These are designed only to hold up to foot traffic. Sliding heavy machinery around will scrape them off, and hot car tires will peel them away from the surface. Paints designed specifically for garage floors are your best choice. They’re available in three types:
Latex is the easiest to apply. A gallon should cover approximately 250 to 300 square feet. You’ll also need to prime the surface as recommended. Manufacturers have improved these paints greatly, making them more durable and less susceptible to “hot-tire pickup.”
One-part epoxy paints offer increased durability over latex. They cure when exposed to air, adhere better than latex, and resist wear well. Expect to pay $30 per gallon to cover 300 square feet. Again, a primer coat may be required.
Two-part epoxies come with paint and a hardener that you mix together right before you’re ready to coat the floor. These generally cost more, but come the closest to the industrial coatings applied in factories and other high-use areas. A gallon covers about 250 square feet. Primer isn’t usually necessary. Our kit came with small color flecks that we tossed on over the wet paint. They add a bit of traction, and dress up the floor, too.