Why is the grout in my shower coming out?

By Simon Beames, The British Remodeler — 26 years tiling, Schluter-certified, working to TCNA standards in Colorado Springs.

It depends on why it’s coming out. Here’s how to tell the difference.

The usual causes

Too much water in the mix. The big one, and it happens at installation. Grout powder needs a measured amount of water. Add too much — or keep wetting the joints while wiping off — and the cement ends up weak, chalky and porous. Fine on day one; powdering out within a couple of years. If your grout scratches with a fingernail, that’s very likely it.

It was never sealed, or the sealer died years ago. Cement grout is porous by nature. It drinks water every shower, then dries, then drinks again. Sealer slows that cycle; it isn’t magic and it doesn’t last forever. Unsealed grout in a twice-a-day shower is on a countdown from the day it went in.

Movement. Tile and grout are rigid. Houses aren’t. If the floor underneath flexes — weak subfloor, joists spanning a bit too far, a tray that moves a fraction when you stand in it — something has to give, and the grout line is the weakest point. Movement cracking shows up in a pattern: the same corner, the same row, cracking again months after you repaired it. Grout doesn’t crack in the same place twice by accident.

Harsh cleaners. Those limescale removers and mould sprays that promise miracles are usually acidic, and acid eats cement. Use them weekly for a year and you’ve been slowly dissolving your own grout lines. The grout goes rough, then recessed, then starts dropping out of the bottom of the joint first. Related reading: if cleaning has left a film on the tile itself, see what grout haze is and how to remove it.

Age, plain and simple. Well-mixed, well-sealed grout in a solid shower can do fifteen years or more; a badly mixed one in a flexing shower can be gone in three. Even good grout is a wear surface — it doesn’t owe you forever.

Cosmetic failure or waterproofing failure?

This is the part that matters, because the fix is completely different.

Grout is not the waterproofing. In a properly built shower there’s a waterproof layer behind or under the tile; the grout is just the finish. Grout coming out of a sound, waterproofed shower is ugly and wants redoing, but the house isn’t rotting while you decide.

Signs it’s probably cosmetic:

• The grout is powdery but the tiles are firm — no hollow sound when you tap them, no movement.
• Crumbling is mid-wall or mid-floor, not concentrated at corners and the floor-to-wall joint.
• No staining on the ceiling below, no musty smell, no swollen skirting outside the shower.

Signs it’s gone deeper:

• Tiles sound hollow, rock slightly, or the floor feels spongy underfoot.
• Mould that comes straight back within days of a proper clean — that’s often moisture feeding it from behind the tile, not dirt on the surface.
• Water marks on the ceiling below, peeling paint or swollen trim on the wall next to the shower, a damp smell that never quite leaves the room.
• Cracks concentrated where the wall meets the floor and in the corners — those joints take the movement and they’re where water gets in first.

If you’ve got two or three of the second list, stop thinking about grout. The waterproofing has likely failed, and no amount of fresh grout seals a failed membrane.

What a proper fix actually involves

For genuine cosmetic failure, the job is unglamorous but straightforward:

1. Rake out the failed grout. All of it in the affected area, down to a clean, sound depth — usually at least two-thirds of the tile thickness. Diamond blade on a multi-tool, or a hand rake for small areas. Slow, dusty work — and skipping it is where most DIY regrouts fail before they start.
2. Regrout with a correctly mixed grout. To the manufacturer’s ratio — stiff, not soupy — and cleaned off without flooding the joints. Most “my new grout failed too” stories are the original mistake repeated with fresh powder.
3. Seal it once cured, and treat resealing as maintenance — every year or two in a hard-used shower.
4. Corners and the floor-to-wall joint get flexible sealant, not grout. Those joints move; rigid grout in a moving joint cracks every time, guaranteed.

Where epoxy grout makes sense: epoxy doesn’t absorb water, doesn’t need sealing, and shrugs off cleaners that eat cement grout. For a shower floor or a hard-used family shower it’s a genuine upgrade. The trade-offs are cost, faster working time, and no forgiveness at install — it needs to go in right first time. It’s also no cure for movement or failed waterproofing; epoxy over a flexing floor cracks out just the same, only now it’s harder to remove.

When it’s a tear-out: hollow tiles, a spongy floor, or water damage behind the wall means the assembly has failed, not the finish. The honest fix is strip it back, deal with whatever’s rotten, rebuild the waterproofing, then tile — see bathroom remodeling for how that rebuild should be done. Nobody wants to hear that, but regrouting a failed shower buys months, not years — and the rot keeps spreading behind the new grout while you feel better about it.

What NOT to do

Don’t smear new grout over old grout. A thin skin over a cracked, contaminated joint has nothing to bond to and no depth to key into. Tidy for about a month, then it shells off in flakes — the single most common wasted weekend I see.

Don’t caulk over grout lines and call it fixed. Sealant has its place — corners and changes of plane, as above. Run down a grout joint, it’s a bandage over an open question: it hides how bad the joint is getting and makes the eventual proper repair messier. If the grout is failing because water’s getting behind the tile, the caulk just hides the leak while it carries on.

Don’t keep scrubbing at it with acid cleaners. If the grout is dissolving, the cleaner may be the cause. Switch to a pH-neutral cleaner before you do anything else.

When to call someone in

If it’s one wall, firm tiles, dry room — rake out, regrout, seal: a capable DIY job, have a go. Call a tiler when tiles sound like a drum when tapped, when the floor moves, when there’s staining or smell outside the shower, or when the same crack keeps coming back. Those signs mean the problem lives behind the tile — where the expensive damage happens quietly.

I’m a one-man operation here in Colorado Springs — if you want a straight opinion on whether yours is a regrout or a rebuild, ring me on 719-521-8312. I’ll tell you if it’s a weekend job you can do yourself, too.

Related: What is grout haze and how do you remove it? · More from the blog