Have a small cloakroom. Solid walls, no cavity. External window wall is about 12 feet X 12 Feet. Radiator under window. Was going to redecorate and found under window and at both sides seriously damp with paper peeling off. Behind the radiator, under the window, actually was a piece of plasterboard. Very damp. The plaster was boast up to about four feet. Maybe the term is blown. I chipped it off expecting to find a soaking wet wall. Wall is bone dry everywhere along under the window and up both sides. Where could the damp have come from. Can it be condensation behind a working radiator? There is the gas boiler on one side of the wall but I have checked all round it and even the condensation pipe through the wall and all ok and dry. Behind the radiator are the heat reflecting silver panels. Can anyone shed any light on this puzzle?

needawin, October 2011

Have a look at the rear of the foil panel if plastic type material it could be that sweating condensation causing the damp through lack of air circulation.

Something you could try. re-plaster wait for it to dry
Slide a hardboard panel of same size down between wall and foil panel to isolate the foil panel from the cold wall, it may cure it and as the board is not plastic should be sweat free. Check it after around 3-4 days

If this doesn't work then contact local council Engergy saving or planning department tell them the problem and is there any advice they can give.
Your name: Bob

bob, October 2011

is the bleed vavle on the rad tight? might be spraying out when the rad get hot, water must be comming from the rad or its fittings, or is it the water running in from the window still. ??

hh, October 2011