Damp inside on a cavity wall

7 Aug 2009
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United Kingdom
Hi there,

I've got a problem with damp in our downstairs loo. There has always been a little bit of black mold on the wallpaper ever since we moved 10years ago but i'd put this down to it being a cold external corner of the house which was poorly heated as the radiator in there hardly worked. Had the central heating fixed and the problem seemed to go away for a few years. However the toilet cistern still ran with condensation when it was really cold outside, i put this down to the cold mains water entering the cistern when you flushed. Over the past 6 months i have noticed the damp has got a lot worse and the plaster is now blown along the entire length of the wall aprox. 25 feet. I've checked the external wall and the outside ground level is about 12" below the dpc and the floor level inside is another 6" above the dpc. the external brick work and mortar looks good, and what i can see of the dpc looks ok. The external wall is cavity with sprayed in insulation.

Spoken to a couple of specialist damp proofing companies and they all want to inject the external wall and treat it, despite there being no issue with.

My question is as all the visible bits of the external dpc all seem ok could the internal cavity wall's dpc have failed. can this be treated? will it be berried in the concrete floor slab which will need digging up along the perimeter. This could be an issue as part of the effected wall has the stair case on it
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Ok, with these problems it is always best to approach the problem with a process of elimination one step at a time. Start with the easy things you can do, which are mostly free or cost very little, and quite often solve the problem of damp.

Do not rush to the worst case scenario and spend money for a solution you may not need. You are correct to be wary about "damp specialists" wanting to immediately inject a dpc at this stage.

Read a lot of the recent posts on damp and how to change living habits to avoid it.


and read these...


http://www.bolton.gov.uk/sites/DocumentCentre/Documents/Condensation and Mould.pdf

I suspect this is just internally created damp.

You say you have a small radiator in the room. However this room, I suspect, due to its size and a cold cistern will cool down quite quickly, especially in winter...therefore while the radiator is on, the warm air can retain much more moisture........when the radiator goes off, this room may cool down very quickly, all the moisture in the air will condensate on the cold cistern and walls. The temperature changes in the room and lack of ventilation may therefore be causing and exacerbating the damp.

It seems that you need to ventilate the room a lot more that you are and keep a more consistant temperature ( this may be difficult in such a small room as it will cool down fast). However with regards to ventilation, the best solution is to get an extractor with a humidistat in there.

Do you get condensation elsewhere in the house?

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