Cracked Or Crumbling Grout In A Bathroom

People often treat grout as the thing keeping water out of the wall. It is not. Grout fills the joint and looks tidy, while the waterproofing is meant to be behind the tiles. That distinction matters, because grout that cracks, powders or falls out is usually a symptom of movement, a poor mix or a wet substrate rather than a problem in its own right. Regrouting a joint that is still moving simply resets the clock on the same failure.

What the failure pattern tells you

• Straight cracks along one line, usually a corner or where the wall meets the tray or bath. That is movement, and the joint should never have been grouted in the first place.
• Powdery grout that rubs away with a finger. Too much water in the mix, or grouting over a dusty joint, so the cement never gained strength.
• Grout missing in patches on a floor. Deflection in the floor, or tiles that are hollow because the adhesive bed was skimped.
• Dark, damp grout that never dries in a shower. Water is getting behind and the board is likely saturated.

The three real causes

1. Movement joints filled with grout. Every internal corner, every junction with a bath, tray or worktop, and every change of plane needs flexible sealant. Grout there cracks within months.
2. Mixing and preparation. Grout mixed too wet is weak, and joints that were not cleaned out before grouting have nothing to bond to. Both produce a joint that crumbles under a fingernail.
3. A moving or damp substrate. A springy timber floor, tiles laid on plasterboard in a shower, or old adhesive that has lost its grip. The tiles flex a fraction, and grout, being rigid, gives way first.

How to regrout properly

1. Rake out the failed grout to at least two thirds of the tile depth with a grout rake or a multi tool blade, keeping to the centre of the joint so tile edges are not chipped.
2. Vacuum the dust out and wipe with a damp sponge. Let the joints dry completely.
3. Check for hollow tiles by tapping. Any that sound drummy need lifting and rebedding first, because grout will not hold a loose tile.
4. Mix a flexible grout to the manufacturer's water ratio, using a measuring jug rather than eye. Let it stand and remix as instructed.
5. Work it in diagonally across the joints with a rubber float, filling fully, then strike off the excess.
6. Sponge clean in stages as it firms, then polish the haze off once dry.
7. Sealant, not grout, in all corners and around the bath or tray, applied to clean dry surfaces.

When regrouting is not the answer

If the tiles behind a shower sound hollow, if the wall feels soft when pressed, or if the grout is wet hours after the shower was last used, water is already behind the tiling. Regrouting seals the visible surface and traps that water in. The proper repair is to strip the shower area, replace any blown board, tank the area correctly and retile. It is a bigger job, but it is the only version that lasts, and we will tell you that at survey rather than take the smaller money.

Keeping new grout in good condition

Let it cure fully before the shower is used, typically 24 hours for grout and longer for sealant. Seal the grout if the manufacturer recommends it, which makes cleaning far easier. Avoid strong acidic limescale removers on cement grout, and squeegee the walls after showering so the joints dry between uses.

Get a tiler to look at it

If your grout keeps failing, there is a reason and it is worth finding. Send us photos through the enquiry form for an honest opinion, or see our tiling and regrouting service. We work throughout Stoke-on-Trent, Newcastle-under-Lyme, Trentham, Stone and Leek with a free survey and a fixed written price within 24 hours.

Common questions