How to get rid of damp and mould

16 Jun 2010
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United Kingdom
Due to poor plumbing, I have had a leak in my downstairs loo which has gone undetected for quite some some time.
The loo is located underneath the stairs and at the lower end of the stair case is a cavity. The cistern is boxed in by tiles so to gain access to it, I've had to cut a hole in the wall to get to it via the cavity.
I have fixed the leak, the pipe had come out of the cistern and when flushed, the water was pouring out all over the floor into the cavity. As a result, the cavity is as damp as nymphs knickers and there is enough mould to make an entire 6 part wildlife series on.

Question: What is the best way to deal with the damp and the mould?
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hack off the panelling/boxing-in so the air can circulate. Burn or skip the rotten stuff. you say it is ground floor. Is it concrete or wood floor?

take up any flooring so the floor can dry out

How is this WC ventilated? Window or extractor?
Fortunately, the damage is only contained to the cavity behind the loo and under the stairs. The WC itself shows no sign of damage. It is ventilated with an extractor fan.

The cistern is boxed in with tiles and the MDF/plaster board behind the tiles is covered in mould. The floor is concrete and utterly soaked. The underside of the stairs themselves are unaffected however some of the support beams are damp though not rotten. The wall on the opposite side of the hole is damp, this is brick and adjoins my neighbours house. The wall in which the hole is cut is plaster board and unaffected.
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the concrete floor and any brickwork could easily take a year to dry. It is essential that you dry out the timber before it rots. You have got to expose it to circulating air by hacking off panelling, boxing-in and plasterboard.

If the WC has an extractor, use that to improve airflow. You might consider buying a more powerfule one until this problem is cured. You could also consider hiring a dehumidifier for a week and putting it in the WC with the door closed, this will do a lot of fast work, but the concrete floor and concealed voids will still hold a lot of water.

Remove any wet or rotten timber. Use Cuprinol preservers (spirit based) once the wood is dry enough to absorb it.

The concrete floor slab may be damp for some metres around, including adjoining rooms. Vinyl flooring or rubber-backed carpet will prevent it drying, wooden or laminate flooring will warp or rot.

If you are worried about the cost consult your household insurance policy which should cover damage caused by water escaping from fixed installations.

Also warn you neighbour as he might suffer rot due to your leak. He will have to expose and ventiate any voids on his side. If dry rot takes hold it will cost thousands.

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