If you aren't happy with the color of your grout, change it. For this project, you'll need a product known as sulfamic acid (figure A). It's hazardous, so carefully read the precautions on the label before using it. Wear rubber gloves, safety glasses and a respirator approved by the National Institute for Occupational Safety and Health (figure B) when using it. Also, make sure to have a fan pulling air out of the room you're working in. Lightly brush sulfamic acid onto the grout, and allow it to sit for 10 to 15 seconds. Flush thoroughly with water to remove sealants and mineral deposits. Dry the grout with a sponge or towel. Allow the grout to dry for another 15 to 30 minutes, then begin applying grout coloring. Use a foam brush to apply the coloring directly to each grout line (figure C). Allow it to cure for at least 30 minutes but no more than 2 hours. Then rinse the coloring off the tiles. Use a nylon scrub pad to remove any residual color from the tiles.
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