The myth or the mess? There is no doubt that ‘rising damp’ is widely known to be a massive nuisance. It is also known that some believe it to be a myth! It is also widely known when anything porous makes contact with water it will absorb this water. Now think of the materials your house is made from. The most common materials, brick and stone are porous; now think how long ago your house was built. That’s how long it has been absorbing water into the structure, and that water soaks up through the porous materials into the walls and floors. Most houses would have a damp proof course to prevent this BUT for various reasons they fail to work correctly.
These include the damp course not being installed properly, or more commonly the damp course being bridged. By this we mean although the damp course is in place and in perfect working order something is causing the water to be absorbed above the dpc rendering it useless in certain aspects.
The water will next travel up and through the walls. This is then where it begins to affect the inside of the house. The walls will become damp and cold to the touch, and it can also leave unsightly tide marks on the walls. The plaster and paint can become loose; it will be stained and damaged with salts. The effects of rising damp rarely exceeds more than one meter in height.
Rising damp is a seasonal effect. It will increase in winter when water tables rise and falling in summer when the weather is usually dry. This will be shown by the problem becoming worse in the winter months and seemingly disappearing in the summer. All walls contain some form of moisture. This is known as the moisture content MC. If the MC is less than approx 5% at the base of the wall, it is unlikely to be severely affected by rising damp.
The cure
Depending what the source of the rising damp is will depend on the extent of the remedial work needed. You should NEVER only mask the problem. Imagine if you just hid the walls affected with some battens and plasterboard. You won’t see the problem that will be left to fester until it eventually starts to show through the work that Calvin the cowboy left you with.
The most obvious task is to make sure that there is no soil, brick pavers, patio slabs, etc. (a very common problem) that have been laid to the external walls and is higher than the actual DPC itself. Your DPC should be approx 6-8 inches above the external ground level as this allows for splash back of rain water against the property. Our help page shows what else to check for before you approach the route of installing a new DPC.
Whether you have to reduce the external ground level, or you have to install a new DPC the work shouldn’t stop there. If the inside render/plaster has been affected it SHOULD NOT just be left to dry out and redecorate.
Water from the soil usually contains a low concentration of soluble salts, and the rising water will also dissolve salts from the bricks or the mortar. When evaporation occurs, the salt solution becomes more concentrated at the surface and finally, the salts will crystallise out.
The fluffy white stuff on the walls ring any bells? If these salts are hygroscopic, they will absorb moisture from the air which will, then make the area wet during wet weather. This means the wall won’t be able to dry out properly as the salts will always attract any moisture it can. Just by removing the salts from the wall with a scraper or cleaner won’t solve the problem but will in the short term seem to have fixed it. The plaster and render will need to be removed. The new internal plastering should act as a barrier to residual salts and moisture through the wall. A salt resistant additive to the base coat or a salt resistant render is best. GYPSUM based undercoats should not be used unless a suitable renovating plaster is used first. The final plaster coat can be applied using a gypsum based plaster if again applied to a suitable base coat. Re-decorating should be left as long as possible. Wall paper should not be hung for approx 6 months.
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