Cracked wall and rainwater leak

28 Jun 2004
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United Kingdom
I've got an external wall following on from the boundary wall. When the (brick) wall and (block) extension was built about 4 years ago the builder put in a DPM in the extension wall at the same level as the boundary wall, but left a bit sticking out and cement/sand plastered over it. Now there is a crack along (about 4 metres long) where the DPM sticks out on the extension. Water has seeped in through the crack and what looks like salty deposits has appeared on the internal plaster.

Whats the best way to fix the problem on the outside and inside of the extension wall?
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you say he rendered over the DPM! :eek: effectively bridging the DPM, this is bad practice!

sounds like damp is getting into your walls via the external render and making it's way into your plaster inside, you need to act quickly or you will need a re-plaster internally too, the white on your plaster is efflorescence, salty deposits, not harmful and can be brushed off once the damp has been stopped, basically the moisture coming through the wall is bringing salt with it and when the water evaporates it's leaving the salt on the plaster.

you need to get the render off the outside and fit a bellcast bead ABOVE the DPM level and apply new render from the bead up to where you hacked off.

hope this helps

One question. The deposits on the inside is a small patch (about 60cm diameter circle), I was going to take off this plaster, apply salt neutraliser and replaster. Is this a good/worthwhile idea?
fix the outside first to stop anymore damp coming in THEN let the inside dry out completely and brush off efflorescence then check if plaster is sound and hasn't blown, plaster will only need re-doing if it's no good and so long as the damp has been sorted you'll get no more probs
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