Damp Proofing & Damp Treatment in London

Penetrating damp enters through the fabric: a failed gutter, cracked render, defective pointing, a leaking roof or a blocked cavity. It usually appears as a patch that grows in wet weather and dries in fine weather, and it can appear at any height on the wall.

Rising damp is drawn up from the ground through masonry and stops at a fairly consistent height — typically under a metre — often with a visible tide mark and salt deposits. It is far less common than it is diagnosed, and a great deal of injected damp-proof course has been installed in houses that did not have it.

Condensation forms on the coldest surfaces in the room — external corners, behind furniture, around window reveals — and is usually accompanied by black mould. It is a ventilation and heating problem, not a fabric problem, and no amount of damp-proofing the wall will fix it.

Injecting a damp-proof course into a wall suffering from penetrating damp does nothing, because the water is coming from a gutter rather than the ground. Re-plastering over it hides the stain until the plaster fails again. The money is spent twice and the cause is still there.

The most common real cause in London terraced property is external ground level having been raised over the years — new paving, a raised patio, or a build-up of soil bridging the original damp-proof course. Lowering the ground level often does more than any treatment applied to the inside of the wall.

Where the cause is external — guttering, pointing, render, roof, ground level — the fix is to the fabric, not the wall surface. Once water is no longer getting in, the wall dries and the internal finish can be made good.

Where a damp-proof course has genuinely failed and needs replacing, the internal plaster affected by salts usually has to come off and be replaced too, because contaminated plaster continues to draw moisture from the air regardless of whether the wall beneath is dry.