By Frank Davey, a building surveyor from Allman Woodcock in Norwich
My client told me that the water came up to the first step of the cellar so I trusted his word and walked in. The step was over a foot deep and my welly wasn’t, so the results don’t need spelling out. Yes, the cellar had a flood. In fact the trouble was caused by the level of the water-table, not a plumbing leak or rainwater problem as I’ve more often found. In a sense, then, we had true rising damp. There are those who say that rising dampness doesn’t exist. They obviously don’t live in Norfolk, or occupy houses built on sand at the top of a hill. Otherwise they’d have found that the local soft red brick is very porous and will soak water up just like one of those plant oasis things used to keep flower arrangements moist. Building laws say that any property built after 1875 should have a damp proof course (dpc) installed, but around here I don’t find it in many houses built before the First World War. Early dpcs were slate and later bitumen, more recently a plastic sheet will be used. Where a dpc is missing an injected chemical can provide the necessary barrier, but don’t spend the money just for the sake of it. I’m quite into conservation and agree with those who say that dampness in an old building should first be dealt with by lowering the outside ground level or controlling the internal environment. However, that ignores the fact that as dampness rises into the brickwork it carries salts, which are then are left in the wall as the water evaporates away. The result is dampness caused by the salt, so that approach might not be a cure. Actually, an injected dpc doesn’t cure those salt-caused dampness problems either. If you don’t mind peeling plaster and paint, fine – leave things alone. Do avoid the mix of moisture and wood because that’s not fine at all. That’s how wood recycles, which is great for ecology but bad for buildings. By the way, if you have a converted animal barn the salts are not only ground salt, but cow pee too…Have you ever wondered why a hard, cement-rich render is used to re-plaster walls after a damp proof course has been injected? It helps to hold back the salts, and even mask rising dampness itself. Don’t ever just re-plaster in cement to treat rising dampness, it will only drive moisture higher up the walls. Hard cement render is not good for our local red brick, if used both inside and outside and the result can be a dampness sandwich, with corroded electric socket boxes and rotten floor joists. Not good. Just an introduction on this subject, but I’ve run out of space and you’ve got a wall to check.
Frank’s on 01603 610243.