by Refresh PSC »
Sun May 06, 2012 1:15 pm
I'm obviously posting blind with this thread as I can't physically see the symptoms you're experiencing but I'll tell you what I'd normally check with these signs. It may help you locate the problem.
The following checklist is based on you saying the problem was on an external facing upstairs bedroom so we can rule out rising dampness;
1. Check the pointing. Missing mortar will provide a route for any ingressing moisture which will then dissipate and pop up in sporadic areas on internal plasterwork.
(Also as a footnote to this point, if the mortar is a lime mortar which is highly absorbent, it can track through to your internal side of the wall. If the internal plaster is also lime based (Original plaster) this can easily become damp without any visible signs of ingress point.) Theoretically, you will have an absorbent passage for moisture tracking in from outside.
If the mortar is lime based, leave it as is but if the internal plaster is lime based, replace it with a waterproof sand and cement render.
2. The location and condition of your guttering downpipe and the type of brackets holding it onto the wall can sometimes be a problem. If it is in the local area of the damp problem, check to see if it is made from plastic or cast iron. Cast iron pipe brackets screw deep into the masonry and as such can provide a route for any rainwater hitting that external wall.
3. If you have a loft expansion tank, check it and its associated pipework for any leaks that may be feeding onto that wall. You'll be surprised on how many times I've found a leaking loft tank causing upstairs dampness.
4. Guttering, fascia boards, faulty, missing tiles and any flashing that are allowing rainwater passage into the wall.
You'll normally find that if none of the above points are relevant, re-plastering incorporating a waterproof chemical such as Sika 1 will normally do the trick. I do not advise sealing the external face of walls unless absolutely necessary as brickwork is designed to breathe on the external face allowing natural evaporation of residual moisture.
Hope this helps.