Archive for February, 2012

Chemical damp-proof courses – Cure all or Catch all?

Wednesday, February 29th, 2012

Useless dpc inserted well above floor level

You must have seen them; tell-tale rows of mortar spots or brown plastic caps running from one end of the street to the other. Our terraced housing stock is full of them.
Soundly built, often with hard clay bricks, such homes have stood for over a century without rising damp; so why now?

Built with open fires and no central heating, with draughty sash windows, not sealed upvc and on washdays the back door wide open to let all the steam out. The houses could ‘breathe’. Draughts blowing in round the windows shot up the chimney taking the moisture-laden air with them.

Modern living and ‘saving the planet’ has put an end to all that. Those sturdy old houses are now molly-coddled with draught-proofed windows, loft insulation, they’re now hermetically sealed boxes in which we shower, cook and breathe out moisture-laden air.

The bricks haven’t changed, nor have the ground conditions or the coal cellars would be flooded, so why have the walls become so damp? Condensation Doh!

Our over-heated, super-sealed homes store up the moisture with no way out but to condense on the coldest place in the room – low down on the outside wall. And to make matters worse this is just the place, under the window, where years of condensation on old single-glazed windows, with no window cill to speak of, has run-off onto the plaster.

Old plaster under windows, even under the bedroom windows, is often loose or perished, the result of condensation from old windows, and I defy any rising damp to rise that high.

So why all the fuss? Why install a new dpc? Usually because some ill -informed mortgage lender insisted when his valuation surveyor reported the lack of a dpc.

And why wasn’t this error highlighted and the malpractice stamped out? Because inexperienced surveyors ‘copped-out’ and recommended referral to and ‘expert’, and the ‘experts’ were the very companies selling the product! It was a money machine.

And, to make matters worse, if you really had rising damp the stuff was no good and badly installed.

Tests have shown clay bricks are so dense that it is almost impossible for water to rise through them; the mortar bedding or the plaster facing are the most likely paths.

Clay bricks are so dense that hardly any of the damp-proofing solution can be absorbed anyway; not enough to block all the pathways, if there were any.

And so what if the wall gets a bit damp? It could rot any joist ends built in to the wall. But the joists in most terraced houses run side-to-side not front –to-back.

Even then, how often have you seen the neat row of holes half way up the front wall, way above the floor joists? They’re there just for show.

If you think you have a damp problem remember that ‘rising damp’ is Very rare. There is usually some other cause like condensation, a leaking gutter, a split rainwater pipe or a leaking washing machine hose to name but a few so, if you can’t find the cause yourself give us a call.