Regrouting a Shower: Walls, Floor, Corners and Cure Time Done Right

To regrout a shower, first confirm the tiles are solidly bonded and the pan or waterproofing is not leaking. Then cut out the old grout to at least two thirds of its depth without touching the membrane, regrout walls before the floor, leave the inside corners and tub or pan line open for silicone, and keep water off the shower for at least 72 hours (longer for some products).

Before you remove anything: four checks

Shower regrouting fails most often because the grout was a symptom. Water that has been getting behind the tile for years has already done its damage, and new grout simply hides it for a while. Spend an hour on these checks before buying grout.

1. Tap test for hollow tiles

Tap every tile with the handle of a screwdriver or a small plastic mallet. Solid tile gives a sharp, consistent sound. Hollow tile gives a dull, papery or rattling sound. A few hollow corners on otherwise solid tile are common and usually stable. Clusters of hollow tiles, especially on the bottom three rows, beside the valve, or under the shower head spray zone, suggest the bond has failed or the backer is wet.

2. Press test on the walls

Press firmly with the heel of your hand on the lower walls and around the niche and valve. Any give, flex or crunching means the substrate behind the tile is soft. That is common with older showers built on drywall or "greenboard" without a proper membrane.

3. Look for signs of a failed pan

On a mortar-bed shower floor, grout that stays dark for many hours after a shower, a musty smell that returns right after cleaning, efflorescence around the drain, or stains or soft flooring on the ceiling or wall below all point to a pan problem. A traditional pan with a clogged weep system holds water in the mortar bed, and grout over a saturated bed stays dark, grows mildew and crumbles. See grout stays wet or dark and smelly grout for diagnosis.

4. Check the fixtures

Leaks from a valve body, shower arm connection or drain can look like grout leaks. Check behind an access panel if there is one and look at the ceiling below an upstairs shower. Fix plumbing before you regrout.

Removing grout in a shower without damaging the waterproofing

Shower assemblies are thinner than they look. On a modern bonded system, the waterproof membrane (liquid-applied or sheet) sits directly under a thin layer of thinset, often 1/8 to 3/16 inch thick, which is all that separates the bottom of the grout joint from the membrane. A grout blade that goes one pass too deep can cut it. On a traditional mortar bed, the bed itself is usually 3/4 inch or more thick, so floor grout removal is less risky there, but the walls may still be backer board with a membrane or a vapor barrier behind.

Use a carbide hand saw or an oscillating tool with a carbide or diamond grout blade narrower than the joint. Set a depth reference: measure the tile thickness at an edge (a cut tile at a corner or a removed accent tile), and mark the blade or saw with tape at two thirds of that depth. Avoid grinders in showers. The tool choices and dust precautions are covered in how to remove grout.

Remove all old silicone and caulk from inside corners, the tub or curb line, around the valve trim and at the niche. Scrape it out, then wipe the surfaces with isopropyl alcohol so no silicone film remains. Silicone residue repels both grout and new sealant.

Choosing the grout for a shower regrout

A regrout is a chance to upgrade from a basic cement grout. The joint width and the tile surface still decide sanded versus unsanded, and the waterproofing still lives behind the tile, but the right grout makes the shower easier to keep clean. The location-specific guidance is in shower grout and shower floor grout.

On the shower floor, which stays wet longest and gets the most soap and body oil, epoxy grout or a high-performance cement grout is the usual upgrade. Epoxy requires the joints to be dry, which in a shower means at least 24 to 48 hours with no water use after removal and good ventilation. Avoid premixed grouts on shower floors unless the TDS explicitly approves them for continuously wet floors.

Step-by-step shower regrouting

1. Run the pre-checks. Tap and press-test all tiles, look for pan and plumbing leak signs, and resolve anything structural before continuing.
2. Prepare the space. Turn off the water supply if you will be working near the valve, cover the drain with tape (leave a removable cover so debris cannot fall in), and protect the tub or shower base with a drop cloth or cardboard.
3. Remove silicone and old sealant. Cut and scrape all sealant from corners, the tub or curb line and fixtures. Clean residue with isopropyl alcohol.
4. Remove the grout. Cut each joint to at least two thirds of the tile depth, staying clear of the membrane. Clean the tile shoulders with a carbide scribe.
5. Clean and dry. Vacuum all joints, wipe them with a damp brush, then let the shower dry with the fan running. For epoxy, allow at least 24 to 48 hours; for cement grout, joints should be surface dry before you dampen them for grouting.
6. Tape off the movement joints. Put painter's tape or foam backer rod into inside corners, the wall-to-floor joint, and the tub or curb line so grout cannot fill them.
7. Grout the walls first. Dampen the joints lightly, then work one wall at a time from top to bottom with a rubber float held at 45 degrees, packing diagonally across the joints. Mix only what you can place and clean in about 20 to 30 minutes.
8. Tool and clean each wall. When the grout firms, tool the joints to a consistent slightly concave profile and clean with a well-wrung sponge, wiping diagonally. Remove haze within the TDS window.
9. Grout the floor last. Start at the far corner, work toward the exit, and keep sponge water to a minimum so it does not pool at the drain and wash out the joints near it.
10. Remove the tape and clean the open joints. Pull the tape from the corners and change-of-plane joints while the grout is still soft and scrape out any grout that bridged in.
11. Cure. Keep the shower out of use for the time on the grout TDS, typically 72 hours for cement grout. Ventilate, but do not run a heater or fan directly on the fresh grout.
12. Apply silicone. After the grout has cured enough to be dry at the corners (often 24 to 72 hours), apply 100 percent silicone sealant rated for kitchen and bath use to all inside corners, the wall-to-floor joint, the tub or curb line and around fixtures. Allow the silicone its own cure time, usually 24 hours, before water exposure.
13. Seal if appropriate. Seal cement grout with a penetrating sealer once the grout has cured for the time the sealer requires. Epoxy does not need sealing.

Change-of-plane joints: why silicone, and how to do it

Where two planes meet (wall to wall, wall to floor, wall to tub, wall to ceiling) the surfaces move independently with temperature, moisture and the weight of a person standing on the floor or water filling a tub. Grout is rigid and cracks there. The TCNA Handbook method EJ171 calls for sealant, not grout, at these joints. The full explanation is in caulk vs grout movement joints, and the product comparison in grout vs caulk vs silicone.

For a clean silicone joint, keep the joint free of grout to full depth, wipe with isopropyl alcohol, and tape both sides about 1/16 inch back from the joint. Apply a continuous bead, tool it with a gloved fingertip or a plastic tooling tool dipped in a little soapy water, then pull the tape at a low angle immediately. Fill a tub with water before sealing the tub line so the tub is at its loaded position when the sealant cures. Color-matched sealants are available from most grout manufacturers to match their grout colors.

How long to wait before using the shower

Bathrooms are often cool and humid, which slows curing. If the room is under about 60 deg F (16 deg C), add time. The broader cure timeline is in grout cure time, and sealing guidance for showers in sealing shower grout.