Terry’s Guide to Rising Damp Treatment
Last Updated 28 August 2018
What is rising damp?
Rising damp is groundwater that has been absorbed by porous building materials such as brick or mortar. Many people do not realise that water can travel upwards through a building, but if you imagine the bricks acting as a sponge sitting in a shallow pool of water, it’s easy to see how this happens.
What causes rising damp?
Building regulations have required all houses built since 1875 to have a damp proof course (DPC) built into the walls. A DPC is a layer of water-resistant materials which block water from spreading upwards, originally made from a mix of hard stones such as slate or flint, while modern homes use layers of PVC plastic. A failed or – in very old buildings – missing DPC allows rising damp to spread up above the habitable level.
Buildings in areas with a high groundwater level and are more likely to have problems with rising damp, and the more porous its materials, the more water will be absorbed.
How to spot rising damp
Like all forms of damp, rising damp is most easily spotted by discolouration of the affected walls.
The difference with rising damp is that the discolouration will start at the floor and have a clear stopping point where the water reached as far as it could. Often, this point has a white, powdery line along it formed by salts carried up from the ground and building materials, called a “tide mark”.
These salts – known as hygroscopic salts – cause problems of their own. They constantly absorb water, causing your walls to become damp not just from the ground but from moisture in the air around them being absorbed as well.
Other signs are peeling paint, crumbling, soft-to-the-touch plaster and mould. Skirting boards becoming damp or peeling off the walls are another common symptom, and, in extreme cases, there may be a layer of standing water on the ground.
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How to treat rising damp
Rising damp is a problem that affects almost every building in Britain, but it’s also a problem that’s been thoroughly solved. A DPC will stop water from travelling up the walls, so our first step (after we’ve confirmed it’s definitely rising damp – it’s frequently misdiagnosed) is to check that a DPC has been installed and, if it has, find where it has failed.
Sometimes the DPC is installed too low, allowing groundwater to rise above it, or sometimes building works have created gaps in the DPC, forming a “bridge” that groundwater can travel along. Either way, we’re fully equipped to provide a permanent solution to your rising damp problems, whether your DPC just needs to be patched up or it requires a complete installation.
Next, we remove any damp paint or plaster all the way to the brickwork so that it can dry out. We may also have to replace pointing that has been corroded by the groundwater. In more severe cases where there is structural damage, we may have to brace the basement while we carry out structural repairs – but these cases are very rare.
Once our moisture meters tell us the problem has been solved, we reapply the plaster and paint to get it looking as good as new.