Mould is not a cleaning failure, it is a building physics problem. It needs moisture, a surface below the dew point and time. Remove any one of those three and it cannot grow. Most bathrooms we are called to have all three in abundance, and in nearly every case it is fixable during a refit at very little extra cost.
First, work out which problem you have
Condensation shows up on the coldest surfaces: single glazed window reveals, the corner of an external wall, the ceiling above the shower, and behind furniture. It is worse from October to March and better in summer. Penetrating or plumbing leaks stain from a point and spread, they often show on the ceiling below, and they are constant regardless of season. Rising damp is far rarer than people think and shows as a tide mark low on a ground floor wall.
Diagnosing this correctly is the whole job. Fitting a bigger fan will do nothing for a leaking shower tray, and resealing a tray will do nothing for a cold ceiling.
Cause one, not enough extraction
A ten minute shower releases roughly half a litre of water into the air. If the fan is undersized, badly ducted or switched off with the light, that moisture stays in the room and condenses. Fixes: a fan sized above the 15 litres per second minimum, rigid short ducting, a humidity sensor and a 15 minute overrun, and a 10mm gap under the door so replacement air can enter.
Cause two, cold surfaces
Solid brick walls in Victorian and 1930s Stoke housing sit close to outside temperature in winter, so warm damp air condenses on them instantly. Options during a refit include insulated tile backer boards on external walls, upgrading a cold single glazed window, and adding underfloor heating so the room does not swing from freezing to steaming twice a day. Steady background warmth is far better at preventing condensation than short blasts of heat.
Cause three, failed seals and joints
- Silicone applied over old silicone rather than cut back to clean substrate.
- Grout used in movement joints, which cracks and lets water through behind the tiles.
- A bath sealed while empty then filled, opening the joint every time it is used.
- A shower tray on an unsupported or flexing floor.
- Missing or poorly installed tanking behind a tiled shower.
Once water gets behind tiles it soaks the board, and no amount of resealing the visible joint will dry it out. That is why patch repairs so often fail within months.
Cause four, how the room is used
Drying washing on the towel rail, keeping the door open so moisture spreads to cold bedrooms, and running the shower with the fan off all add up. None of these are the customer's fault exactly, but a well designed bathroom tolerates them and a badly designed one does not.
Putting it right during a refit
- Strip back to substrate and inspect for hidden saturation, replacing any soft or blown board.
- Insulate cold external walls with tile backer boards.
- Fully tank the shower area and reinforce all corner junctions.
- Install correctly sized extraction with rigid ducting and humidity control.
- Use flexible grout, and sanitary grade silicone at every movement joint.
- Fill the bath before sealing it, so the joint is formed at maximum deflection.
- Add gentle background heat, ideally underfloor, on a timer.
Maintenance that actually helps
Squeegee the shower glass and tiles after use, which takes twenty seconds and removes most of the water before it can evaporate. Leave the fan to run its overrun rather than switching it out at the isolator. Keep the door closed while showering and for a few minutes after. Check the external grille once a year for dust and cobwebs. Replace silicone every five to seven years as a matter of course, it is a consumable rather than a permanent fixture.
Get the cause diagnosed properly
If your bathroom keeps going mouldy, we will look at it and tell you honestly whether it is ventilation, insulation, sealing or a genuine leak. Free survey, fixed written price within 24 hours, and repairs or full refits carried out in house by our own insured Stoke-on-Trent fitters.
Common questions
Why does black mould keep returning on my silicone?
Because the mould is growing in the silicone itself, not on it. Once the surface is colonised, bleach only removes the colour. The joint has to be cut out and replaced with a sanitary grade silicone.
Is my mould condensation or a leak?
Condensation appears on cold surfaces such as window reveals, external corners and ceilings, and it is worse in winter. A leak stains in one place, spreads outward and does not care what the weather is doing.
Will a dehumidifier solve it?
It helps as a stopgap but it treats the symptom. Correct extraction removes the moisture at source, which is a permanent fix rather than a nightly chore.
Does anti mould paint work?
It slows regrowth on a surface that is otherwise dealt with. On a cold, poorly ventilated wall it buys you months, not years.
Can insulation help?
Yes. Raising the surface temperature of a cold external wall above the dew point stops condensation forming there at all. Insulated backer boards behind tiles are an effective option during a refit.
Do you fix mould as part of a refit?
Yes. We identify the cause first, then correct extraction, cold bridging, sealing and substrate as part of the work rather than covering it over.