How to Clean and Seal Slate Floors

Kitchen with slate flooring

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Slate flooring may literally be as hard as a rock, but it does require regular maintenance to look its best. There are several common cleaners and cleaning tools you can use on slate—as well as some you should never use. When it comes to stains, a household agent usually does the trick. And while regular cleaning is important for looks and to prevent undue wear on the flooring, sealing the slate (and grout joints) is the best way to protect this porous stone from stains and everyday dirt. 

The most important thing you can do regularly to maintain a slate floor is to keep it free of loose dirt and debris. These small particles can act like grits of sandpaper, wearing down the protective sealer and making tiny scratches in the tiles every time the floor is walked on. You can clean slate floors regularly with a dust mop, a broom, and a damp mop. Ideally, you should dust mop your slate floor every day, and damp mop it once a week. Apply a sealer every three to five years, or as recommended by the manufacturer.

Tools and Supplies You Will Need

  • Dust mop
  • Broom and dust pan
  • Mop and bucket
  • Mild dish soap (optional)
  • Rubbing alcohol or hydrogen peroxide
  • Sponge
  • Stone floor stripper (as needed)
  • Stone and grout sealer
  • Shallow plastic pan
  • Grout sponge
  • Clean cotton cloths

Instructions

Dust Mop the Floor

Dust mop the entire floor with a high-quality, machine-washable dust mop. Start at one end of the floor and push the mop toward the other end, using the same motion for the entire floor. Do not move the mop back and forth because it will simply spread around the dirt and grit. Work in defined sections at a time, and sweep up the line of accumulated dirt and grit before moving on to the next section.

Mop the Floor

Damp mop the floor with a high-quality washable mop and plain water. For occasional deep cleaning, you can also add a few drops of mild detergent, such as dish soap or fabric detergent for delicate fabrics (such as Woolite) to the wash water. Don't allow large puddles of water to form, and don't leave water on the surface. If you use a detergent in the water, rinse the floor thoroughly with plain water. Let the floor dry completely before walking on it.

Remove Stains

Spot-treat stains with ordinary isopropyl rubbing alcohol and water. Mix 1/2 cup of alcohol with 1 quart of water. Dip a sponge into the solution and wipe at the stain. If necessary, scrub the stain with a towel or cloth. Alternatively, use a cleaning solution of a few drops of hydrogen peroxide mixed with a quart of water, applying it with a sponge and/or towel.

Prepare to Seal the Floor

Plan to seal the floor if it is unsealed or is ready for a fresh coat of sealant. If the floor has traces of an old sealant or it has been waxed, you may need to use a chemical stripper to thoroughly clean the surface. Wax can be removed with a wax stripper. Other types of sealer, such as acrylic or urethane coatings, may require strong solvent strippers, and you may want to leave this to a stone flooring or restoration professional.

If you applied the original sealant (or you had a professional do it), contact the sealer manufacturer or flooring professional for recommendations. You may not need to strip the sealer in this case.

Choose a Sealer

Choose a sealer based on the type of slate you have, the amount of traffic the floor gets, and the desired look of the floor. There are two basic types of sealant that can be used on a slate floor. A below-surface, or penetrating, sealer will seep down into the material, clogging the pores so that stains cannot get in. A surface or barrier sealer creates a clear protective coating over the surface of the stone, rather than soaking in.

Surface sealers have a more visible finish than penetrating sealers. Because penetrating sealers leave the stone looking more natural, they are preferred by most homeowners.

Apply the Sealer

Make sure the floor is completely clean and dry. Pour a small amount of penetrating sealer (as applicable) into a shallow plastic tub. Swish the sealer around gently so it coats the bottom of the tub, then tip the tub so the sealer pools at one side of the tub. Dip a grout sponge (use a small grout sponge, or cut a large one in half, if desired) into the bottom of the tub—away from the pool of sealer—to add a thin layer of sealer to the sponge. Rub the sponge over the tile and grout in circular and back-and-forth motions to cover all surfaces. Work in a small area of about 3 by 3 feet. Let the sealer sit for three to five minutes, or as directed by the manufacturer.

Buff the Floor

Immediately buff the sealed area with a clean cotton cloth or towel to work the sealer further into the title and grout and remove excess sealer from the surface. Repeat the same process of applying sealer, letting it sit, then buffing to seal the entire floor. Overlap each new section onto the previous section so that the wet sealer blends with the neighboring sections. If desired, apply a second coat of sealer after the recommended drying time.

What Not to Use on Slate Floors

Never use acidic or abrasive cleaning products when mopping a slate floor or when spot-cleaning stains. Acidic cleaners, including ordinary vinegar, cause a chemical reaction that can etch the stone. Strong cleaning agents can strip the sealer on slate and grout. Also, never use oil-based cleaners or dust-mop treatments. Oils can make the floors slippery and can clog up the crevices and textured surface of the stone.