Evidence grade: B1 — Trade practice
Regrouting and recaulking are two different jobs done in one weekend: scrape out failed grout between tiles and pack in fresh grout, then strip the old caulk where tile meets tub and lay a new 100% silicone bead. Grout fills the flat joints; caulk seals the moving ones.
Effort: Moderate · 1–2 days (mostly cure time) · grout saw or oscillating tool with grout blade, grout float, sponges, buckets, polymer-modified grout, 100% silicone caulk, painter's tape, rubbing alcohol
PPE and ventilation
Wear safety glasses and a dust mask (respirator if using a power tool for grout removal), plus gloves when handling cleaners. Ventilate the bathroom — run the exhaust fan and open a window if there is one; silicone caulk fumes are strong until cured.
Decide whether this job applies
Regrouting fixes cosmetic failure: crumbling, cracked, or permanently stained grout and moldy caulk. It does not fix what's underneath. If tiles sound hollow when tapped, move underfoot, or the wall feels soft, the substrate or waterproofing has failed — that is a rebuild, not a regrout. Stop and call a tile professional.
Step 1 — Remove the old grout
Use a grout saw (or an oscillating multitool with a grout-removal blade) to take out at least 1/8 inch of grout, or about half the tile depth — new grout needs something to bite into, not a skim coat over the old. Vacuum out the dust. For the caulk at the tub-tile joint and corners, cut it away completely with a utility knife: fresh caulk will not bond to cured caulk residue, and a bead laid over old caulk fails within weeks [1][2].
Step 2 — Clean and dry the joints
Wipe the stripped joints with rubbing alcohol to remove soap film and residue, then let everything dry thoroughly — at least 30 minutes of air-drying, longer if the joint was wet behind the old seal. One pro tip worth following: run a small fan in the tub for up to 24 hours after stripping, because walls are often damp behind the tile from years of small leaks, and no caulk bonds to a wet surface [2].
Step 3 — Mix and pack the new grout
Mix polymer-modified grout per the manufacturer's instructions to a thick paste, and let it slake up to 10 minutes. Holding a grout float at 45°, press grout firmly into the joints from multiple directions — pass over the area at least three times so every line is filled to depth. Then flip the float to 90° and scrape off the excess. Work fast: you have roughly 5 to 20 minutes before the grout starts setting on the tile [1]. Choose sanded grout for joints wider than 1/8 inch (it resists cracking); unsanded for narrower joints [1].
Step 4 — Sponge, then caulk the moving joints
Once the grout is firm to the touch and doesn't stick to your fingers, wipe the tiles with a well-wrung damp sponge, rinsing often — dried grout haze is nearly impossible to remove later. Then caulk the joints that move: where tile meets the tub, and every inside corner. Cut the nozzle at 45°, lay a continuous bead of 100% silicone (tape both sides of the joint first for a clean line), smooth it with a damp finger in one pass, and pull the tape immediately [1][2]. Grout is rigid; it cracks in corners and at the tub line, which is why these joints get flexible caulk instead.
Step 5 — Cure and seal
Let grout and caulk cure 48 hours before heavy use (caulk feels dry in about 30 minutes but isn't a full waterproof barrier yet). Once cured, wipe off any remaining grout haze and apply grout sealer along the lines — it extends the grout's life and slows staining. Reseal every year or two in a shower that sees daily use [1].
Stop rules
- Stop and call a pro if tiles are hollow, loose, or shifting; the wall behind them is soft; or water damage is visible around the surround. Regrouting over a failed substrate hides the damage while it gets worse.
- Stop if the grout joints are narrower than about 3/16 inch and you've never done this before — the risk of chipping tile edges is high; this one is worth hiring out (practitioner guidance).
- Do not use the shower until the cure window has passed. Running water over half-cured silicone can wash it out of the joint.
Honest limits
- Regrouting is cosmetic and waterproofing-adjacent, not structural. It stops surface water intrusion at the joints but cannot repair a failed shower pan, missing waterproof membrane, or rotted backer board.
- Silicone caulk is the durable choice for wet joints, but it is harder to replace later than acrylic-latex — This Old House magazine's own recommendation leans acrylic-latex for easier future replacement [2]. Either is acceptable; silicone lasts longer between replacements.
- New grout color rarely matches aged grout exactly — take a chip of old grout to the store when matching, or plan to regrout the whole area [1].
Sources
- Angi — "How to Regrout a Shower and Make It Look Like New" (updated July 7, 2026) — https://www.angi.com/articles/how-to-regrout-shower-tile.htm?p=345
- This Old House — "How To Caulk a Bathtub" (Tom Silva) — https://www.thisoldhouse.com/bathrooms/how-to-caulk-a-bathtub
Repair Lab · Release 1 · Evidence last checked September 30, 2026 · A project of AOJEL