How to Repair Cracked or Missing Grout in Tile Floors and Showers

Learn how to remove damaged grout, mix and apply new grout, and seal it properly so your tile stays waterproof and looking clean for years.

Cracked, crumbling, or missing grout is not just an eyesore — it is a slow-moving invitation for water damage. Every gap between your tiles is a channel that lets moisture seep down to the substrate below, where it can rot the underlayment, loosen the tile bond, and create a breeding ground for mold.

The good news is that repairing grout is one of the most satisfying DIY jobs you can tackle. It requires almost no experience, a handful of inexpensive tools, and you will see a dramatic before-and-after difference in under two hours.

This guide covers everything from identifying whether your grout actually needs repair to finishing with a proper seal.

How to Tell If Your Grout Needs Repair

Not every grout problem is the same. Before you buy supplies, figure out what you are dealing with.

Cracked or crumbling grout. If you see visible cracks running through the grout lines, or if the grout flakes away when you rub it with your finger, it has lost its structural integrity. Water is already getting through — repair now.

Missing grout. If you can see gaps where grout has completely fallen out, you have a direct path for moisture. Fix these areas before your next shower or floor mopping.

Mold-stained grout that is still solid. If the grout is firmly in place but discolored with black or pink mold, you do not need to replace it — you need to clean it. A hydrogen peroxide and baking soda paste, scrubbed with a stiff brush, will usually restore it. Reserve full replacement for grout that is physically failing.

What You Will Need

Sanded vs. Unsanded Grout — Pick the Right One

Using the wrong grout type is the most common DIY mistake. Here is the simple rule:

Sanded grout contains fine sand particles that add strength and reduce shrinkage. Use it for grout lines wider than ⅛ inch (3 mm) — which covers most floor tiles and many wall tiles.

Unsanded grout is smooth and flows more easily into narrow joints. Use it for grout lines ⅛ inch or narrower — common for polished wall tile, subway tile, and glass tile.

When in doubt, measure your grout lines with a coin. A dime is about 1/16 inch thick. If your grout line is wider than a dime, use sanded grout. If it is narrower, use unsanded.

Step 1: Remove the Old Grout

This is the most tedious part of the job, but doing it right determines how well the new grout will hold.

Using a grout saw. A manual grout saw (about $8 at any hardware store) has a carbide-tipped blade that scrapes out old grout. Hold it at a slight angle and work along the grout line in short strokes. Go about ⅛ to ¼ inch deep — you do not need to remove every last speck, but you need enough depth for the new grout to bond.

Using an oscillating multi-tool. If you have a larger area (over 10 square feet), an oscillating tool with a grout-removal blade cuts the job time by more than half. Set the depth guide so you do not scratch the tile edge.

Vacuum the dust. After removing the old grout, vacuum all joints thoroughly. Any dust left in the gaps will prevent the new grout from bonding.

Step 2: Mix the New Grout

Follow the manufacturer’s instructions on the box exactly. In general:

1. Pour the grout powder into a clean mixing container.
2. Add water slowly while mixing with a margin trowel or stir stick.
3. Aim for a “peanut butter” consistency — stiff enough to hold its shape but soft enough to spread. If it is soupy, add more powder. If it is crumbly, add a tiny bit more water.
4. Let the mixed grout sit for 2–3 minutes (“slake”), then stir again before applying.

Step 3: Apply the Grout

Hold the rubber grout float at a 45-degree angle to the tile surface and spread the grout diagonally across the joints. The diagonal motion forces grout into the gaps rather than dragging it out.

Work in sections of about 2–3 square feet at a time. Press firmly — you want the joints completely filled with no air pockets.

After you have filled a section, hold the float at a steeper angle (almost 90 degrees) and scrape off the excess grout from the tile surface, again working diagonally.

Step 4: Sponge the Excess

This step separates a clean job from a mess. Wait 15–20 minutes after applying the grout — the grout should be firm in the joints but not hard on the tile surface.

Wet your grout sponge and wring it out until it is just damp — not dripping. Wipe the tile surface in a circular motion, rinsing and wringing the sponge frequently. The goal is to remove the haze from the tile faces without digging into the joints.

You will need 2–3 passes with clean water to get a haze-free surface. Let the grout cure for 24 hours before walking on the floor or using the shower.

Step 5: Seal the Grout

After 24–48 hours of cure time (check the manufacturer’s recommendation), apply a penetrating grout sealer. Grout is porous — unsealed grout absorbs spills, soap scum, and moisture like a sponge.

Pour a small amount of sealer into a disposable dish and apply it with a small foam brush directly onto the grout lines. Avoid getting sealer on the tile surface — it can create a cloudy film that is difficult to remove.

Let the sealer penetrate for the time specified on the bottle (usually 5–10 minutes), then blot any excess with a clean cloth. Sealed grout repels water and stains and needs reapplication every 1–2 years.

Common Mistakes to Avoid

• Skipping the sealer. Unsealed grout in a shower or kitchen floor will stain permanently within months. Sealer is not optional — it is the final critical step.
• Using too much water when sponging. This is the #1 cause of weak, crumbly new grout. Keep the sponge damp, not wet.
• Not removing enough old grout. If you leave a thin layer of old grout in the joint, the new grout may not bond and will pop out within weeks.
• Mixing too much grout at once. You cannot save mixed grout for later. Mix small batches and accept that you may need to mix again.

When to Call a Pro

Most grout repairs are well within a homeowner’s ability, but there are two situations where a professional is the right call:

1. The tile itself is loose or hollow-sounding. If tiles move when you press on them, the problem is not just the grout — the tile bond has failed. You need a tile contractor to re-set the tiles before regrouting.
2. Water damage is already visible below the tile. If you see soft drywall, peeling paint on the ceiling below a second-floor shower, or warped baseboards near a tile floor, the damage has already spread beyond the grout. Address the underlying leak first.