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How to match grout for a bathroom tile repair

It’s not too hard to match grout color if you invest a little time and effort. (Tim Carter)

I’m about to remodel a bathroom. I’ll be switching out a shower stall and know my tile floor will have to be patched. Fortunately, the previous owner left behind lots of tile for me, but there’s no grout. I’m afraid that if the grout doesn’t match, the repair will stand out like a sore thumb. What’s worked best for you when you have to match grout on your jobs? — Karen J., Marblehead, Mass.

You should locate that past homeowner and give her/him a huge hug. It was quite thoughtful to leave behind some of the extra building materials. I did that with my last home whenever I could. In my case, I used oversized brick to build my chimneys. Knowing it would be almost impossible to locate in the future, I saved about 50 bricks for a future homeowner should they need them for any reason.

Matching interior grout can be a challenge, but it’s not impossible. As with most things, if you want perfection, you need to invest some time and effort. I agree with you about how important it is to match both the grout color and texture. No matter how wide the grout lines are, if they don’t match you can see it right away.

The matching process starts by deep cleaning the grout. I’ve had the best success doing this with oxygen bleach. This is a powder you mix with hot tap water. Once all the powder is dissolved, you pour the solution onto dry grout allowing it to soak and bubble for about 15 minutes.

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At the end of the wait period, you scrub the grout vigorously with a stiff nylon scrub brush. Be sure the brush bristles touch the grout. Don’t use a flimsy toothbrush. You want to really scrub. The longer you allow the oxygen bleach solution to soak, even up to an hour or more, the less you have to work. If the solution soaks into the grout while you wait to scrub, add more so that a film of solution is on top of the grout.

Rinse the floor after cleaning to ensure all the dirt is up. Allow the grout to dry overnight. You can usually tell if you got the grout clean by looking at the edges of the floor where no foot traffic has touched it. The grout along walls and in corners usually is much cleaner than where you walk. If all the grout looks the same color at this time, you can start the matching process.

Before you buy new grout, make sure what type you have. Grout can be sanded or unsanded. Sanded grout contains fine silica sand and Portland cement. Unsanded grout is just Portland cement. Dry pigments are added to both types to create the colors you see.

Sanded grout is easy to spot because you can see the tiny bumps of sand in the texture of the grout. Unsanded grout is very smooth.

The time of day to match grout color is midday. If you try to match grout color at night, the color temperature of the lightbulbs in the bathroom can interfere with your ability to get a perfect match. Some incandescent bulbs are available that render a color temperature close to the natural sunlight toward the middle of the day. Consider using those if you have to match when the stars are shining.

Get samples or a color chart of new grout and hold it next to your existing grout. If you can salvage a chunk of existing grout from under a baseboard next to a wall, this is the best way to start the matching process. The original tile setter undoubtedly put grout at the edges of the floor before the wall trim was installed. Pry off a piece of baseboard and see whether you can get a chunk of the grout.

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The color of the grout out of the bag before you add water to it is the color it’s going to be once dry. You can prove this by mixing up some new grout and allowing it to dry. Add just enough water to the dry grout to make it the consistency of stiff applesauce.

Often you can’t get a perfect match from one bag of grout or one brand. You may be forced to do some creative mixing and blending of different colors of grout to get a match. This requires great discipline and diligence as you need to be very exact in your measuring, blending and mixing as you create test batches. Record-keeping is everything in this exercise.

When you add water to the dry grout, the color gets deeper, and it can be frightening. This is why you need to mix up a test batch and allow it to dry before you commit to the actual grouting of your new tile.

If you’ve never grouted before, realize that water is both your friend and foe. You need water to mix and clean up the mess on the tile. But too much water will ruin the new grout.

Water in excess during the mixing process or as you clean and strike the joints will dilute the amount of Portland cement in the mix. If you allow this to happen, the grout will crumble and crack over time.

Properly mixed unsanded grout is the consistency of slightly warm cake icing. As mentioned earlier, you want sanded grout to be the consistency of stiff applesauce. When you wipe off excess grout from the tile surface, the grout needs to be somewhat stiff in the joints. I urge you to watch the four-part grouting tile video series at my website to see how to do this. Use this handy URL:

If you touch the fresh grout too soon, the sponge will remove grout, creating a depressed grout line. Squeeze out all the water you can from the rounded grout sponge before you allow the sponge to touch the tile.

Need an answer? All of Tim’s past columns are archived free at You can also watch hundreds of videos, download Quick Start Guides and more.