Regrouting is one of those jobs homeowners put off for years because it sounds like tile work, and tile work sounds expensive. In practice it's patience work. Most of the day goes into removing the old grout; the new grout goes in fast. A single shower stall is a realistic Saturday project, and the materials cost less than a decent dinner out.
Shower joints come in two kinds, and they fail differently. The joints between tiles on a flat run of wall or floor are grout. The joints where two planes meet — inside corners, the line where the wall meets the tub or shower base, around fixture escutcheons — should be flexible caulk, because those joints move slightly and hard grout cracks there on schedule.
If the black growth and cracking live only in the corners and the base line, you don't need this project. Scrape out the old caulk and run a fresh bead instead. Our walkthrough on getting mold off shower caulk covers when caulk can be cleaned versus when it has to be replaced. Regrouting is for field joints that are crumbling, powdery, cracked out in chunks, or stained so deep that cleaning no longer touches them — and for surface grime alone, try how to clean grout first, because it's a much shorter job.
One stop sign before you start: press on the tiles around the bad grout. If tiles flex, sound hollow over a wide area, or the wall behind a tile feels soft, water is probably behind the tile already. New grout over a waterlogged wall buys you a prettier failure. That situation needs the wall opened up, not regrouted.
| Your joints | Use | Why |
|---|---|---|
| Under 1/8 inch wide | Unsanded | Flows into narrow joints and packs fully |
| 1/8 inch and wider | Sanded | The sand keeps wide joints from shrinking and cracking as they cure |
| Marble, glass, or polished stone tile | Unsanded, whatever the width | Sand scratches soft and glossy surfaces |
Most modern bagged grouts are polymer-modified, which flexes a little and sheds water better than old-school cement grout — a good default for a shower. Epoxy grout is tougher and shrugs off stains, but it's unforgiving to install and costs several times more. For a first regrout, standard modified grout is the sane choice.
Dig out the old grout. Cut down the center of each joint, then angle the blade to free the shoulders. Remove at least 1/8 inch of depth — roughly two-thirds of the joint — so the new grout has something real to grip. A shallow smear is the exact failure this job exists to avoid. Keep the tool moving and let it do the work; forcing it is how tile edges get chipped.
Clean the joints. Vacuum the dust out, then wipe with a damp sponge. Dust left in the joint weakens the bond and speckles the finished color.
Mix a small batch. Add powder to water — not the other way around — and mix to a peanut-butter consistency: it should hold on the float without slumping off. Let the batch rest 5–10 minutes (this rest is called slaking), then stir it again without adding water. Mix only what you can place in about 30 minutes.
Pack the joints. Hold the float at about 45 degrees and push grout across the joints with firm diagonal strokes, pressing hard enough to fill them completely, no voids. Work an area you can finish before the grout starts to stiffen.
Wait, then sponge. Give it 15–30 minutes, until the grout has firmed up and doesn't stick to a fingertip. Wipe with a barely damp sponge in diagonal strokes, rinsing the sponge constantly — dirty water goes in the first bucket, clean rinse water in the second. Too much water at this stage washes pigment out and weakens the surface.
Remove the haze. After an hour or two, a dull film forms on the tile faces. Buff it off with a dry microfiber cloth. Haze still hanging on the next day usually gives up to a nylon pad and patience.
Let it cure untouched. Keep the shower dry for at least 24 hours, and go by the bag — many products want 48–72 hours before the shower goes back into regular service. No sealing yet, either.
Seal the grout, caulk the corners. After the full cure window, apply grout sealer to the field joints per its label. Then run silicone caulk in the corners and along the tub line — those moving joints were never grout's job to begin with.
Grouting over the old grout. A skim coat has nothing to lock into. It looks fine for a month, then comes out in flakes — the single most common reason regrouts fail.
Caulking everything. Caulk smeared across field joints peels, traps moisture behind it, and turns a grout problem into a mold problem.
Rushing the cure. A long hot shower at hour 12 can soften and wash out fresh grout. The fix for this one is free: just wait.
Cleaning too aggressively, too soon. Acid cleaners — vinegar included — attack fresh cement grout. For the first few weeks stick to water and a mild cleaner; after that, our guide to removing hard water stains covers which cleaners are safe on which surfaces.
Dig it out deep, pack it in fully, wipe it gently, and give it time to cure. Do those four things and a regrouted shower commonly goes a decade or more before the grout needs real attention again — and next time around, it'll probably just be the caulk.
At least 24 hours, and many grout labels specify 48–72 hours before regular use. The grout feels hard long before it has cured through, and early soaking is the easiest way to shorten its life. When in doubt, follow the bag over anyone's impatience — including yours.
No — not as a surface coat. Fresh grout needs depth to lock into, at least about 1/8 inch of cleared joint. There are specialty bonding products that claim otherwise, but skim coats are notorious for flaking out within the year. The removal step is most of the work because it's most of the job.
For a standard stall, pros often charge a few hundred dollars, with the price climbing if tiles need resetting or the corners need extensive work. Doing it yourself, materials commonly run under $50–$75 if you already own a multi-tool — which is why this job is such a good DIY candidate.
Standard cement-based grout, yes — a penetrating sealer after the full cure window slows water and stain absorption a lot. Some premium grouts are sold as pre-sealed, and epoxy grout doesn't need it. The bag tells you which kind you bought; believe the bag.
The usual causes: movement joints (corners, tub line) got grouted instead of caulked, the grout was mixed too wet and cured weak, the old grout underneath was left too shallow so the new layer never bonded — or there's water behind the tile moving the whole assembly. Match the crack pattern to the cause before redoing it the same way.