Mould on grout and tiles: the deep-clean method
Can you deep-clean mould out of grout?
Yes, in most cases. Mould on glazed tiles sits on the surface and wipes away. Grout is different: it's a porous, slightly rough cement that holds water and lets mould grow into its top layer, so it needs a cleaner left long enough to work and a brush to get into the lines. Silicone sealant is the exception. Once mould has stained the inside of the silicone, no amount of scrubbing removes it, and the joint needs replacing.
Why the lines go black and the tiles don't
Water runs off a glazed tile but sits in the grout, especially in the bottom rows of a shower and the horizontal joints where droplets collect. Soap and shampoo residue builds up in the same places and gives mould something to feed on. Where tap water is hard, as it is in much of Cyprus, a film of limescale roughens the surface and holds even more moisture. Cracked or missing grout lets water behind the tiles altogether, which is a bigger problem than anything you can see.
The deep-clean method
- Ventilate the room, and wear gloves, a mask and eye protection.
- Dampen the grout first; never brush mouldy grout while it's dry.
- Apply a mould cleaner suitable for grout and leave it for the time given on the label.
- Work along each line with a small stiff brush, such as a grout brush or an old toothbrush.
- Rinse thoroughly, dry the tiles and joints with a towel, and leave the fan running until everything is dry.
Use one product at a time. Bleach and acidic cleaners such as descalers or vinegar must never be mixed, because together they give off a harmful gas. Bleach brightens the tile and lightens the stain but tends to do less on porous grout; what bleach does and doesn't do to mould explains why. Acids, vinegar included, can etch marble, limestone and travertine, so check what your tiles are made of before trying vinegar on mouldy grout.
Silicone: replace, don't scrub
Black spots that stay after cleaning are inside the sealant. Cut the old silicone out with a sharp blade, clean the joint and deal with any mould underneath, then let it dry completely, ideally overnight with the fan on, before running a fresh bead of mould-resistant sanitary silicone. Keep water off it until it has cured for the time stated on the tube. Sealing over a damp or mouldy joint simply traps the problem in.
When to re-grout
Re-grouting is the answer when lines are crumbling, cracked or missing, when stains survive two or three thorough cleans, or when mould is back within days. Raking out the top of the old grout and filling with fresh grout gives a clean, sound surface. If tiles sound hollow when tapped, feel loose, or the wall on the other side shows damp, water is already getting behind them; signs of mould inside a wall covers what to look for next.
Keeping it clean
Once the grout is clean and fully dry, a penetrating grout sealer slows the absorption of water and makes the next clean easier. After each shower, squeegee the tiles and run a towel along the bottom of the screen and the silicone line. Keep shampoo bottles in a caddy rather than on the tiled ledge, where they trap water underneath. Run the extractor until the mirror clears. The same routine works for a kitchen splashback behind the sink.
When it spreads beyond the tiles
If the grout is the only problem, the steps above usually keep it under control. When mould also appears on the ceiling, around the window or on painted walls, the whole room is too damp, and tackling mould across the whole bathroom is the next step. For lines that keep turning black despite all this, a damp check of the shower wall and the rooms around it gives moisture readings and a written report with the quote, so you know whether to re-grout, fix a leak or improve the extraction.
Grout mould keeps coming back? book an inspection from €75 or call +357 99 759144.