What You Need to Do Before You Start
Replacing grout means removing the old material between tiles and filling those gaps with new grout. The process takes a full day or two depending on the size of the area, and you will need to keep the new grout dry for at least 24 hours after you finish. Most people can do this themselves with basic tools—a grout saw, a grout float, a sponge, and a bucket—and the cost is usually under $50 for materials.
Before you begin, decide whether you are replacing all the grout in a space or just repairing a few cracked lines. Full replacement takes longer but gives a uniform look. Spot repairs work well if only a few joints are damaged. Either way, the steps are the same; you are just choosing how much area to cover.
Key Takeaways
- Remove old grout with a grout saw or rotary tool, cutting along the joint until the gap is empty and clean.
- Mix new grout to a peanut butter consistency, let it sit for 10 minutes, then mix again before explore.
- Press grout into the joints with a grout float held at a 45-degree angle, then scrape off excess before it hardens.
- Wait 24 to 48 hours before exposing the grout to water, and seal it after it cures if you are using unsanded grout in a wet area.
Removing Old Grout Safely
Use a grout saw (a small hand tool with a carbide blade) or a rotary tool with a grout blade to cut out the old material. Hold the tool at a slight angle and run it along the joint, pressing firmly but not so hard that you crack the tile edges. Work slowly—rushing causes the blade to jump and gouge the tile. If you are working on a large area, take breaks; this step is tiring and accuracy matters more than speed.
For shallow grout lines, a grout saw alone works fine. For deeper joints or stubborn grout, a rotary tool (like a Dremel) with a grout-removal bit cuts faster, though it creates more dust. Wear a dust mask and eye protection either way. Once you have cut along the entire joint, use a small chisel or the corner of a putty knife to pop out any remaining chunks. The joint should be empty, clean, and roughly rectangular in cross-section.
Vacuum or brush out all dust and debris from the joints. If the tiles are porous (like natural stone), dampen them lightly with a sponge so they do not pull moisture from the new grout too quickly. Do not soak them—just a light mist is enough.
Mixing and explore New Grout
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 soft enough to spread. Too dry and it will not fill the joints; too wet and it will sag and crack as it dries. Most bags tell you the ratio on the label; follow it as a starting point and adjust from there.
Let the mixed grout sit for 10 minutes (this is called slaking), then stir it again for 30 seconds. This second mix activates the cement and makes the grout easier to work with. Do not add more water at this point. If the grout seems too stiff after slaking, a few drops of water is acceptable, but resist the urge to thin it too much.
Load a grout float (a flat tool with a handle, usually 4 to 6 inches wide) with grout using a margin trowel. Hold the float at a 45-degree angle to the wall or floor and press the grout firmly into the joints. Work diagonally across the tiles so you are not dragging grout out of the joints you just filled. Fill one section at a time—roughly 3 to 4 square feet—before moving on.
Cleaning Excess Grout
After you have filled a section, wait 15 to 20 minutes for the grout to firm up slightly. It should be hard enough that your finger does not sink into it, but still soft enough to cut. Hold the grout float at a steeper angle (nearly vertical) and scrape diagonally across the tiles to remove the excess. This is the most important step for a clean finish—grout left on the tile surface hardens and becomes very difficult to remove later.
Once you have scraped the excess, dampen a large sponge (not dripping wet, just damp) and wipe the joints in a circular motion. Rinse the sponge frequently and wring it out well. You are not trying to remove all the grout, just the haze on the tile surface. Wipe too aggressively and you will pull grout out of the joints. After the grout firms up more (usually 3 to 4 hours), you can do a final light wipe with a barely damp sponge to clean any remaining haze.
Drying Time and Sealing
Do not walk on the floor or splash water on the grout for at least 24 hours. In cool or humid conditions, wait 48 hours. The grout continues to harden for weeks, but it needs to be fully set before it meets water. If you are working in a bathroom or kitchen, close the door and keep humidity low if possible.
After the grout cures, you may need to seal it. Unsanded grout (used for thin grout lines, usually less than 1/8 inch) is porous and should be sealed in wet areas like bathrooms and kitchen backsplashes. Sanded grout (used for wider joints) is denser and does not always need sealing, though sealing extends its life. Follow the grout manufacturer's instructions—some sealers go on after 48 hours, others after a week. Grout sealer is a straightforward brush-on process that takes 15 minutes and prevents stains and water damage.
Common Mistakes to Avoid
The most common error is leaving too much grout on the tile surface. It hardens like concrete and becomes a nightmare to remove. Scrape and wipe as you go, not after everything is dry. Another mistake is mixing too much grout at once. A full bucket can harden before you use it all, especially in warm weather. Mix smaller batches—you can always mix more.
Do not rush the removal step. Cutting grout out slowly and carefully prevents tile damage. Cracked or chipped tile edges are permanent and much more expensive to fix than taking an extra hour to remove grout properly. Finally, do not expose new grout to water too early. Patience here prevents the grout from washing out or cracking.
Tools and Materials Checklist
| Item | Purpose | Notes |
|---|---|---|
| Grout saw or rotary tool | Remove old grout | Grout saw is slower but safer; rotary tool is faster but dustier |
| Grout float | explore new grout | 4 to 6 inches wide; rubber or plastic works best |
| Margin trowel | Load grout onto float | Small flat tool, 2 to 3 inches wide |
| Sponge | Clean excess grout | Large, soft sponge; not a scrubbing sponge |
| Bucket | Mix grout | 5-gallon bucket works for most jobs |
| Grout powder | Fill joints | Unsanded for thin lines, sanded for wide joints |
| Dust mask and eye protection | Safety | Grout dust is silica; protect your lungs and eyes |
Frequently Asked Questions
Can I use caulk instead of grout?
No. Caulk is flexible and designed for gaps that move; grout is rigid and designed for gaps that do not. Caulk will not hold up in tile joints, especially in wet areas. Use grout for tile and save caulk for the corners where tile meets wall or tub.
What is the difference between sanded and unsanded grout?
Sanded grout contains sand particles and is stronger, making it better for wide joints (1/8 inch or wider). Unsanded grout is smoother and works for thin joints (less than 1/8 inch). Using the wrong type can cause cracking or poor appearance. Check your tile spacing and the grout bag label to choose the right one.
How long does grout take to dry?
Grout is usually firm enough to walk on after 24 hours, but it continues hardening for up to a week. Wait at least 24 hours before exposing it to water, and 48 hours in cool or humid conditions. Full cure takes longer, but the grout is functional after 24 hours.
What if I crack a tile while removing old grout?
Stop when ready and work more carefully around that tile. If the crack is small, you can sometimes seal it with grout or caulk once the new grout is done. If the crack is large or the tile is loose, you will need to replace that tile before grouting. This is why slow, careful removal is worth the extra time.
Do I need to seal grout after it dries?
Unsanded grout in bathrooms and kitchens should be sealed to prevent stains and water damage. Sanded grout is denser and does not always need sealing, but sealing extends its life. Check the grout manufacturer's instructions—they will tell you whether sealing is recommended for your product and how long to wait before explore sealer.