I’ve long loved concrete floors. I like their zero-maintenance appeal, their industrial look that gets better with time, and—though they work well with radiant underfloor heating (see our Remodeling 101 on the topic)—I even like the feeling of a cool floor underfoot, especially when temperatures rise.

But I’ve recently found a flaw in concrete floors—something that had never occurred to me until I attempted to remediate the situation: If your concrete floors are stained, their color is quite literally “set.” In my apartment, that’s an inconsistently applied, dusty red. If you want to change it, you’ll need to put in either major money or elbow grease.

To wade through the options, I talked to Anthony Zamora of C Rock Finishing in Oakland, California—here’s what I learned.

Above: San Francisco interior designer Nicole Hollis had new concrete floors poured in her 5,000-square-foot studio. For the rest of the space, see A Noirish Studio for a San Francisco Design Star. Photograph by Laure Joliet, courtesy of Nicole Hollis.

How easy is it to change the color of stained concrete floors?

Not very. “Concrete is like a big rock sponge,” Zamora says. “Before it has anything on it, it wants to soak up everything.” Meaning that whatever has already been applied to your concrete floors has fundamentally changed the material and will affect coloration going forward. This is a generalization, of course—but when floors are “stained,” or more accurately, treated with a penetrating sealant, the color has been absorbed to an unknown depth.

To change the color, we’re covering the two most common solutions here: You can re-stain the floors (by applying a new penetrating sealant) or paint them (by applying an industrial coating). Other options include staining and then polishing your floors (which achieves a different effect than just re-staining) or covering them entirely with a new material, like a microtopping or concrete overlay.

In an early iteration of the office of SF-based fashion retailer Everlane (see their new space here), the existing concrete floors were re-covered with a new cement layer, a process called microtopping. For more, see Office Visit: The Everlane Studio in San Francisco. Photograph by June Kim, courtesy of Everlane.
Above: In an early iteration of the office of SF-based fashion retailer Everlane (see their new space here), the existing concrete floors were re-covered with a new cement layer, a process called microtopping. For more, see Office Visit: The Everlane Studio in San Francisco. Photograph by June Kim, courtesy of Everlane.

How can I re-stain my concrete floors?

To start, you’ll need to have the existing surface mechanically ground down, both to prime the concrete to accept a new stain and to remove as much of the offending color as possible. “You can’t control how much stain permeated the concrete in the original process,” Zamora says.It could be superficial and come off fairly quickly, or it could have permeated as deeply as half an inch down, which means it’s not going anywhere. You’ll need to mechanically grind your floors to determine your next step.

When Seattle chef Matt Dillon remodeled a bathroom at his farm on Vashon Island, Washington, its concrete floor was preexisting but needed to be demoed when plumbing was added. Dillon and his contractor patched the floor and polished it with acid etching. See more in Bathroom of the Week: A Vintage Bath on Old Chaser Farm on Vashon Island, Washington. Photograph by Aaron Leitz for Remodelista.
Above: When Seattle chef Matt Dillon remodeled a bathroom at his farm on Vashon Island, Washington, its concrete floor was preexisting but needed to be demoed when plumbing was added. Dillon and his contractor patched the floor and polished it with acid etching. See more in Bathroom of the Week: A Vintage Bath on Old Chaser Farm on Vashon Island, Washington. Photograph by Aaron Leitz for Remodelista.

What does it mean to mechanically grind the concrete?

You need to use something harder than concrete in order to grind it down, explains Zamora, which usually means a substrate like metal, ceramic, or resin that’s been impregnated with diamonds. “Diamonds are so strong that they can actually cut up the surface of the concrete.”

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