Damp Proofing Question

Damp in bedroom

I live in a house about 300 years old on the bottom, 22 inch thick stone walls. It was built up in 1924 to become two storey. Upstairs is not stone, think it is brick and all has been rendered and Sandtexed. Main bedroom is damp, and grows black mould. DPC Inspector came and said DPC working well, but it was condensation, we needed to ventilate more. We have had the wall paper taken off the walls, and a "barrier" of a PVA glue and water mixture put on the walls in July. Then painted over the top to allow it to breathe. An elderly parent has the room, with a night storage heater on low, so opening windows is a problem. There is a dehumidifier going 24 hours a day. Still we have black mould appearing and I'm thinking now of putting another "PVA barrier" on top of the paint, then the 2mm polystyrene on top of that, and then paint it again. Do you think this will help? I cannot afford to have someone in to re-plaster. Can anyone help please with any further ideas? Many thanks.

1 Answer

Best Answer

Hi, black mould needs water and heat to grow, water condenses from warm humid air against a cooler surface, painting PVA will not stop it growing.
The dew point of a wall is where the water condenses, any surface that is cooler than the ambient air will allow the water to condense on to it.
So the solution is:
1 have dry air
2 have no heat
3 insulate walls so cold surfaces are minimised.
Obviously it's not practical if someone sleeps in there.
So ventilate, or dehumidify (not both, dehumidifier will suck water from air outside too) insulation is best solution.
Hope this helps
Regards
Brad

Answered 29th Dec 2012

Brad Prenzlau

Member since 31 Aug 2008

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