How to Replace Moldy Grout

Step-by-step instructions for laying in a new coat without disturbing the tile.
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When grout becomes discolored, cracked and chipped, it’s time to replace it. Cracked grout will allow water to get behind or under the tile, which may cause damage. To replace grout around just one tile, you can scrape it out with the pointed end of a bottle opener after first taping off the tiles with blue painter’s tape to prevent scratches. For a larger job, use a grout saw, which can be purchased for about $7. As for the grout itself, buy 10 percent to 20 percent more than you think you need.

To grout it yourself, follow these instructions:

Materials and Tools:

grout saw
vacuum or soft brush
abrasive cleaner
rags
grout (non-sanded for joints smaller than 1/8-inch, sanded for joints 1/8-inch and bigger)
float (or cardboard and putty knife)
citrus-based cleaner
grout sealer

Steps:

1. Working in one 2-by-2-foot area at a time, run the saw up and down the grout line.

2. Vacuum out flaked residue, or use a soft brush to remove the grout pieces.

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3. Put some abrasive cleaner on a wet rag and rub the joint to remove any remaining residue.

4. Mix the grout. Carefully follow the directions regarding the proportions of water and dry ingredients because grout won’t last if it’s too wet when mixed.

5. Lay the grout in the joint with a float, filling the space generously. If you don’t have a float, make a tool with a piece of cardboard and a putty knife. If you’re doing a horizontal surface such as a countertop, work from the back forward. If doing a diagonal surface, work from the bottom up. If you start at the top, the grout will have a tendency to sag in the channel.

6. After the wet grout has set for about five minutes, clean up the tiles with a wet sponge. With a dry rag, carefully wipe only the tile. The grout will set in about 20 minutes and cure in 24 hours.

7. Add a “skin coat” after the first application has dried. This will fill in any tiny holes.

8. Clean the dried grout before sealing it. Use a citrus-based cleaner because bleach will discolor the unsealed grout.

9. Follow the manufacturer’s instructions for applying grout sealer. If you follow the directions, you should never have discolored grout again.

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