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How to Acid Wash a Slate Tile Floor

Claudia Henning

Grouting a slate tile floor can leave lines and streaks across the tile surface. Neutral cleaners will not remove this material. The tile needs to be acid-washed carefully. A mixture of sulfamic acid and water can remove the grouting from the surface of the slate tile. The difficult part is making sure to keep the surface wet and limiting the time that the sulfamic acid sits on the tile. Be sure to neutralize the acid afterwards with baking soda to avoid permanent damage to the tile and grout.

  1. Mix ¾ cup of sulfamic acid crystal with a bucket of water. Industry standard tile-cleaning-strength crystals are available at home and garden centers.

  2. Spray water on small sections of the tile floor using a spray bottle. Apply the sulfamic acid solution to the wet area with a sponge and scrub gently. Allow the acid to soak for two to three minutes.

  3. Rinse the area well using a clean, damp towel. Continue the process over the entire tiled floor. Keep the area you are working on wet.

  4. Mix one cup baking soda with a bucket of warm water. Mop the entire floor with the mixture to neutralize the acid. Rinse with clear water and allow the tile to dry for 24 hours.

  5. Apply a layer of tile sealant with a paintbrush or sprayer. Wait 30 minutes and apply a second layer. Allow 72 hours for the sealant to dry. Reapply the sealant every three to five years.