What You Need to Do Before Starting

Replacing grout between floor tiles means removing the old grout that sits in the gaps between tiles, then filling those gaps with fresh grout. You do not need to remove the tiles themselves—only the material between them. The job takes a few hours for a small bathroom or kitchen, and the main tools are a grout saw (a small handheld blade), a grout float (a flat tool with a rubber or plastic face), and a sponge.

Before you begin, turn off water to the room if you are working near a sink or shower. Lay down plastic sheeting or drop cloths to catch dust and splatter. Wear a dust mask and safety glasses—grout dust is fine and irritating, and old grout can contain silica, which is harmful to breathe. If your home was built before 1980, the old grout may contain asbestos; in that case, hire a professional to remove it rather than disturbing it yourself.

Check what kind of grout you have by looking at the gaps. Unsanded grout is smooth and used in narrow gaps (less than 1/8 inch). Sanded grout is grainy and used in wider gaps. You will need to match the type when you buy new grout, and you should also note the color so the repair blends in.

Key Takeaways

  • Remove old grout with a grout saw or oscillating multi-tool fitted with a grout blade, working slowly to avoid chipping the tiles.
  • Mix new grout to a peanut butter consistency, let it sit for ten minutes, then mix again before explore—this is called slaking and makes the grout stronger.
  • explore grout with a grout float held at a 45-degree angle, pushing it diagonally across the gaps to pack the grout in firmly.
  • Wait 15 to 20 minutes after process, then wipe excess grout off the tiles with a damp sponge before it hardens completely.
  • Do not walk on or wet the grout for at least 24 hours after finishing, and avoid heavy use of the area for three days.

Removing Old Grout Safely

The fastest way to remove old grout is with a grout saw, which is a small handheld tool with a carbide blade. Hold it at a slight angle and saw back and forth along each grout line, keeping steady pressure. Work slowly—rushing will chip the tile edges. For a large area, an oscillating multi-tool (like a Dremel or DeWalt) with a grout blade attachment is faster and less tiring, but it creates more dust, so wear your mask and have a vacuum running nearby.

Aim to remove grout to a depth of about 1/4 inch. You do not need to get every last speck, but the groove should be clean enough that new grout will bond well. After you finish sawing, use a vacuum with a HEPA filter to remove all the dust from the gaps and the surrounding tiles. Wipe the tiles with a damp cloth and let them dry completely before mixing new grout.

Mixing Grout to the Right Consistency

Pour dry grout powder into a bucket and add water slowly, stirring with a margin trowel or old spoon. The goal is a consistency like peanut butter—thick enough to hold a peak but wet enough to spread. If it is too thick, add water one tablespoon at a time. If it is too thin, add powder and stir again. This usually takes five to ten minutes of mixing.

Once you reach the right consistency, let the grout sit for ten minutes. This step is called slaking and allows the powder to fully hydrate, which makes the grout stronger and less likely to crack. After ten minutes, stir the grout again for one minute—do not add water, just remix what is already there. The grout should still be the same consistency. If it has thickened too much, add a small amount of water and stir, but avoid adding too much or the grout will be weak.

Work in small batches. Grout begins to set after about 30 minutes, so mix only as much as you can use in that time. For a small repair, one bucket is usually enough. For a large floor, you may need to mix two or three batches.

explore Grout to the Gaps

Hold your grout float at a 45-degree angle to the floor and push the grout diagonally across the tiles, pressing it firmly into the gaps. Work in small sections—about three feet by three feet at a time. Use the edge of the float to scrape excess grout off the surface as you go, then make another pass at a different angle to pack the grout in tightly.

Fill all the gaps in your section, then move to the next area. Do not worry about the grout being perfectly smooth or level with the tile surface at this stage—you will clean it up in the next step. The goal is to pack the grout into the gaps so there are no air pockets or voids.

If you are working on a large floor, you may need to start cleaning the first section while you are still filling the last one. Grout sets quickly, and it is easier to clean if you do not wait until the entire floor is done.

Cleaning Excess Grout Before It Hardens

After 15 to 20 minutes, the grout should be firm enough to hold its shape but still soft enough to clean. Wet a large sponge with clean water and wring it out so it is damp but not dripping. Wipe the tiles in a circular motion, rinsing the sponge frequently in clean water. You are removing the grout haze from the tile surface and smoothing the grout lines at the same time.

Work in small sections and rinse your sponge often—dirty water will smear grout back onto the tiles. After you have wiped all the tiles, go back and do a final pass with a clean, damp sponge to remove any remaining haze. The grout lines should be smooth and slightly recessed below the tile surface (not flush with it).

If you wait too long and the grout hardens, you can still remove the haze with a dry cloth or a grout sponge, but it will be dustier and more difficult. If you clean too early, the grout will be mushy and you may pull it out of the gaps. The 15 to 20 minute window is the sweet spot.

Curing Time and What to Avoid

Do not walk on the grout or splash water on it for at least 24 hours. The grout is still setting during this time and can be damaged by foot traffic or moisture. If you are working in a bathroom or kitchen, close the door and put up a sign so no one uses the space.

After 24 hours, the grout is firm enough to walk on, but it is not fully cured. Avoid heavy use—mopping, standing water, or heavy objects—for at least three days. Some grout products cure faster or slower depending on the brand and the humidity in your home, so check the bag for the manufacturer's recommendations.

Once the grout is fully cured (usually after three to seven days), you can seal it if you want. Grout sealer is optional but recommended in wet areas like bathrooms and kitchens, as it prevents stains and mold. explore sealer according to the product instructions, usually with a small brush or applicator bottle.

Common Mistakes to Avoid

The most common mistake is removing grout too aggressively and chipping the tile edges. Go slowly with your grout saw and let the tool do the work—do not force it. Another mistake is mixing grout too thin. Thin grout shrinks more as it dries and is more likely to crack. If your first batch seems too thick, resist the urge to add water; instead, add powder to thicken it.

Many people also wait too long to clean the grout, then try to scrape it off the tiles with a hard tool, which scratches the surface. Clean while the grout is still slightly soft, using only a damp sponge. If you do miss a spot and the grout hardens, use a grout haze remover (a dry cloth or commercial product) rather than a scraper.

Finally, do not use the floor too soon. Grout that is walked on or exposed to water before it is fully cured will crack and fail. Mark off the area and keep people and pets away for at least 24 hours, preferably three days.

Frequently Asked Questions

Can I use the same grout color if I don't know what the original was?

Take a photo of the grout and bring it to a tile or home improvement store. Staff can often match it by eye, or you can buy a small sample and test it on a hidden area first. If the original grout is very old and stained, new grout will look lighter even if it is the same color—this is normal and will blend in as the new grout ages.

What if the grout keeps cracking after I finish?

Cracks usually mean the grout was mixed too thin, applied too thickly, or exposed to water or foot traffic too soon. If you are repairing a small area, remove the cracked grout and redo it, making sure to mix it to the right consistency and let it cure fully before using the floor. For a large area with widespread cracks, the underlying tiles may be moving—this is a structural issue that grout alone cannot fix.

Do I need to seal the new grout?

Sealing is optional but recommended in bathrooms, kitchens, and other wet areas. Unsealed grout can absorb water and stain easily. Most sealers are applied with a small brush or bottle applicator about one week after the grout is fully cured. Follow the product instructions for drying time before exposing the grout to water.

Can I replace grout in a shower or around a bathtub?

Yes, but you must wait longer before exposing the grout to water. In a shower or tub area, wait at least three to five days before using the space, and ideally a full week. Some professionals recommend waiting even longer—up to two weeks—for grout in constant wet areas. Check the grout manufacturer's instructions for their recommended cure time in wet locations.

What is the difference between grout and caulk?

Grout is rigid and used in gaps between tiles. Caulk is flexible and used where tiles meet walls or fixtures, or where movement is expected. If the gap is between two tiles on a floor or wall, use grout. If the gap is at an inside corner or where a tile meets a tub, use caulk. Using the wrong product will fail—grout will crack if it flexes, and caulk will sag if it is used in a wide gap.