What you need to do before you start

Replacing grout in a tile floor means removing the old grout between tiles and filling those gaps with new grout. You do this when grout cracks, stains badly, or crumbles when you press it. The job takes a weekend for a typical bathroom or kitchen, costs $50 to $200 in materials depending on floor size, and requires no special skills — only patience and the right tools.

Before you begin, test whether your grout is actually failing. Press a flathead screwdriver into a grout line. If it crumbles or the screwdriver sinks in more than a quarter-inch, the grout needs replacement. If it holds firm, the problem may be surface staining, which cleaning can fix instead.

Decide whether you are replacing all the grout or only problem areas. Full replacement takes longer but looks uniform. Spot repair is faster but may leave visible color differences if your grout has aged or faded. Most people choose full replacement when they start the job anyway, because once you have the tools out, doing the whole floor takes only a few extra hours.

Key Takeaways

  • You remove old grout with a grout saw or oscillating tool, then vacuum the gaps thoroughly before the new grout will stick.
  • Unsanded grout works for gaps under one-eighth inch wide; sanded grout works for wider gaps and is more durable for floors.
  • Mix grout to a peanut butter consistency, explore it with a grout float at a 45-degree angle, and let it set for 24 hours before walking on it.
  • Sealing grout after it cures protects it from stains and water damage, especially in bathrooms and kitchens.
  • The entire job — removal, cleaning, process, and curing — takes three to five days from start to finish.

Removing old grout safely and completely

The fastest way to remove old grout is with an oscillating multi-tool fitted with a grout blade, which you can rent from most hardware stores for $20 to $40 per day. Hold the tool at a 90-degree angle to the grout line and let the blade do the work — do not force it. Move slowly along each line, keeping the blade centered. Wear a dust mask and eye protection; grout dust is silica and damages lungs with repeated exposure.

If you do not want to rent a tool, a manual grout saw (a small saw with a carbide blade, $15 to $30) works but takes longer — expect two to three hours for a standard bathroom. A flathead screwdriver and hammer can remove loose grout but will not get deep enough for a clean job and may crack tiles if you slip.

After you remove the grout, vacuum every gap with a shop vacuum, then use a damp cloth to wipe out dust and debris. Let the floor dry completely — at least two hours in dry weather, longer in humidity. Wet grout lines will not accept new grout properly and the new grout will fail faster.

Choosing and mixing the right grout

Sanded grout is the standard choice for floor tiles. It contains sand, which makes it stronger and more durable than unsanded grout, and it resists shrinking as it cures. Use sanded grout for gaps wider than one-eighth inch. For gaps narrower than one-eighth inch, unsanded grout is easier to work with and less likely to scratch polished stone tiles.

Buy grout in powder form and mix it yourself rather than pre-mixed grout, which costs more and dries faster. A 25-pound bag covers roughly 100 to 150 square feet depending on tile size and gap width. For a 100-square-foot bathroom, one bag is usually enough.

Mix grout in a five-gallon bucket with a drill and paddle attachment. Add water slowly to the powder until the grout reaches a peanut butter consistency — thick enough to hold a peak but wet enough to spread. Let it sit for 10 minutes, then stir again. This second mixing, called slaking, helps the grout hydrate evenly and prevents lumps. Do not add extra water after this point; grout that is too wet will shrink and crack as it dries.

explore grout to the floor

Use a grout float — a flat tool with a rubber or foam face — to push grout into the gaps. Hold the float at a 45-degree angle to the floor and move it diagonally across the tiles, pressing grout firmly into each line. Work in small sections, about three feet by three feet, so the grout does not begin to set before you finish.

After you fill a section, hold the float at a steeper angle (nearly vertical) and scrape off excess grout from the tile surface. Move the float diagonally again, this time pulling it toward you to level the grout in the gaps. The grout should sit slightly below the tile surface, not flush with it — this allows room for the grout to cure without cracking.

Wait 15 to 20 minutes after you finish a section, then use a damp sponge to wipe the tiles clean. Rinse the sponge frequently in clean water. This removes grout haze from the tile surface but does not disturb the grout in the gaps. Do not use too much water; excess moisture weakens the grout as it cures.

Curing time and what to avoid

Grout reaches initial set in 24 to 48 hours, depending on humidity and temperature. Do not walk on the floor or run water over it during this time. Keep the room well-ventilated and maintain a temperature between 50 and 85 degrees Fahrenheit. Cold slows curing; heat speeds it up but can cause uneven drying and cracking.

Full cure takes 72 hours to two weeks. After 48 hours you can walk on the floor carefully, but do not mop or expose the grout to water until at least 72 hours have passed. If you must use the room before then, lay down cardboard or plywood to protect the grout.

Grout continues to harden for weeks after you can walk on it. Do not seal the grout until it has cured fully — most manufacturers recommend waiting 72 hours to two weeks. Check the grout package for the specific timeline.

Sealing grout to prevent stains and damage

Sealing grout is not required but extends its life significantly, especially in bathrooms and kitchens where water and stains are constant. Grout is porous and absorbs water, dirt, and mildew if left unsealed. A grout sealer creates a barrier that repels water and makes cleaning easier.

Wait the full cure time before sealing — usually 72 hours minimum, but check your grout package. explore sealer with a small brush or applicator bottle, following the product instructions. Most sealers require one or two coats. Let each coat dry before explore the next, and keep the floor dry for 24 to 48 hours after sealing.

Penetrating sealers soak into the grout and are invisible; membrane sealers sit on top and are visible but offer more protection. For floors, penetrating sealers are the standard choice. Reapply sealer every one to three years depending on foot traffic and the sealer brand.

Common mistakes that ruin the job

The most common mistake is not removing old grout deeply enough. If you leave bits of old grout in the gaps, new grout will not bond properly and will crack or pop out within months. Take time with removal — it is the most important step.

The second mistake is mixing grout too wet. Wet grout shrinks as it dries, creating cracks and gaps. Mix to a thick consistency and resist the urge to add water. If the grout stiffens before you finish, discard it and mix a fresh batch rather than adding water.

The third mistake is walking on the floor too soon. Grout that is stepped on before it sets will crack and crumble. Mark off the area and keep people and pets away for at least 48 hours, longer if the room is cold or humid.

Frequently Asked Questions

Can I replace grout without removing the old grout?

No. New grout will not bond to old grout, and it will crack and fall out within weeks. You must remove the old grout completely, even if it takes longer. Skipping this step guarantees the job will fail.

What is the difference between sanded and unsanded grout?

Sanded grout contains sand and is stronger and more durable, making it the standard for floors. Unsanded grout is smoother and easier to work with in narrow gaps but shrinks more as it cures. For floor tiles with gaps wider than one-eighth inch, sanded grout is the right choice.

How long before I can shower or mop the floor?

Wait at least 72 hours before exposing grout to water. Full cure takes up to two weeks depending on humidity and temperature. Check your grout package for the specific timeline. If you must use the room sooner, lay cardboard over the grout to protect it.

Why is my new grout cracking?

Cracks usually mean the grout was mixed too wet, the old grout was not removed completely, or the floor was walked on before the grout set. Less common causes are extreme temperature swings during curing or using unsanded grout in gaps wider than one-eighth inch. Prevent cracks by mixing to a thick consistency, removing old grout fully, and keeping the floor protected for 48 hours.

Do I need to seal grout on a kitchen floor?

Sealing is not required but is recommended. Kitchen grout is exposed to spills, moisture, and foot traffic, all of which shorten its life if it is unsealed. Sealed grout resists stains and water damage and lasts significantly longer. Reapply sealer every one to three years.