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Damp Patches on Plaster of Exterior Wall After Very Wet Weather

Postby MaveD » Tue Feb 04, 2014 10:30 am

My house is 35 years old with cavity walls. Recently following very wet weather two or three damp patches appeared on the plaster of our upstairs bedroom wall. Once the rain has stopped for couple of days they disappear. Whilst this is an outside wall it does not face the prevailing weather. Can anyone give me some advice as to how to remedy please as my wife has bought some expensive wallpaper which I don't want to hang until this is sorted. Thanks.
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Postby welsh brickie » Tue Feb 04, 2014 4:13 pm

damp patches could be mortar on the wall ties causing damp to bridge the cavity, the only way to tell is to drill the wall and hire a borescope, (fibre optic camera) to look in the cavity,
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Postby oxfordite » Wed Mar 05, 2014 7:46 pm

Additionally, a photo of that area of outside wall, and the gutter(?) above might help in identifying cause.
Do you know what type of lining there is between roof tiles and rafters?
What is the slope angle of the tiles and what type of tiles are used?
Have you got any cavity wall insulation and if so, do you know what type?
e.g. rock wool fibre, blown foam, polystyrene

Things you can likely do towards identifying a problem:
- slide the lowest couple of roof tiles up the roof above the water penetration
- are any tiles cracked, flaking or poorly overlapped?
- is the lining material in good condition?
- does it extend (is it dressed) in to the gutters?
- Are there any signs of rot in the exposed roof timbers?
- Is there a gutter joint above the leak?
- Is the guttering draining freely? or is there a marginal dip above the damp point? (take a bucket of water up and pour it rapidly but without overspilling the gutter... do any joints leak? does any water remain in the gutter? Or can you watch immediately after prolonged rain and see any leaks?)

Is the brick in good shape or is it very porous? is the pointing in good condition - the vertical 'perps' tend to become more porous than the horizontals. A bodge that may aid fixing the problem without identifying it first is to apply Thomsons Water Seal to the dry wall from the problem site right up to the roof. But still need identify where the water is coming from.
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