Bathroom grout is cracking and going mouldy — regrout or re-tile?

Question

My bathroom grout is cracking in places and going black/mouldy no matter how much I scrub. Is it enough to regrout, or do I need the whole bathroom re-tiled?

Tarek H. · Accepted Answer

Don't jump to re-tiling — decide by the state of the tiles, not the grout:

Tiles sound and firmly stuck → regrout and reseal. Rake out the old grout, clean the joints, re-grout with a mould-resistant grout, and redo the silicone in the wet corners. Far cheaper and it looks new.
Tiles cracked, lifting, hollow, or the wall feels soft/damp → the waterproofing has likely failed, which means removing tiles to fix the membrane before re-tiling.

On the mould: if it keeps returning after cleaning, it's usually failed silicone letting water sit, or a waterproofing/ventilation issue behind the tiles — not just surface dirt. Regrout + fresh silicone + better ventilation fixes most cases; chronic damp needs the waterproofing checked. Start with regrout/reseal — it's the cheaper test.

Mariam A. · Answer

Regrouted and redid the silicone in the corners and it looks brand new. The black mould was mostly in old cracked silicone, not the grout itself.

Fatima Z. · Answer

Worth adding for anyone re-doing a bathroom because of cracking/mouldy grout: what's behind the tiles matters as much as the grout. If tiles in a wet zone were fixed straight onto ordinary plasterboard with no waterproofing, moisture gets behind them and you get recurring mould and failure no matter how well you regrout. The correct build in a shower/wet area is moisture-resistant board plus a proper tanking/waterproofing system (or a cement backer board) before tiling — see the thread on moisture-resistant (green) board and why wet zones still need tanking. If you're retiling anyway, it's the moment to get the board + waterproofing right underneath.

Bathroom grout is cracking and going mouldy — regrout or re-tile?

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