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1 October 2020

Rising damp treatments

Rising damp can be expensive to fix. Find out what the treatment options are before you call a professional in.
Damp and mould in home 470621
Liz Ransome-Croker

Rising damp is one of the trickiest types of damp to rectify. You'll probably need to get help from a professional. 

Check your damp-proof course

The first thing to do if you have rising damp is to find out whether you have a damp-proof course and damp-proof membrane, which should stop water from the ground soaking into ground-level walls or floors (see image below).

Regulations making them compulsory in new houses came into force in 1875, so houses built before then probably won't have one. You may be able to spot a damp-proof course by looking for a thin strip near the bottom of the external wall. You'll need to get an expert to confirm this and to try to ascertain whether there is also a damp-proof membrane.

If your home does have a damp-proof course or membrane but is still experiencing damp, then the damp-proofing may have become damaged or worn over time. If they aren't working effectively, you'll need them to be repaired or replaced. 

Repair or insert a damp-proof course

The most common remedy for a missing or damaged damp-proof course is for a builder or damp specialist to drill holes into your wall and inject damp-proof cream to act as a new course. 

But there are alternative solutions, such as cutting grooves into the brickwork and installing a piece of damp-proof course rather than a chemical one. This is more invasive than just drilling holes, so may be less easily hidden. Our damp costs page shows typical prices for both of these jobs.

Repair or replace a damp-proof membrane

If there is just a small patch of damp on your floor, you may be able to remedy it by painting over the patch to stop any more water coming through. You'll need to apply two coats of bitumen latex waterproof emulsion underneath the floor covering, which you can buy from many DIY stores. For extra protection, some experts recommend laying reflective foil building paper (foil-side up) as well before the paint is dry.

This is only suitable for minor cases, though. If the damp is extensive, you may need to have the damp-proof membrane entirely replaced. This is likely to be costly, but may be necessary if the damp is widespread or other solutions haven't worked. 

Check exterior ground level

If you have a perfectly good damp-proof course, your damp problem could be because the ground outside has built up above the damp-proof course, which should be 15cm above ground level. The problem can be solved by digging away excess soil on the exterior side of the damp wall to below the level of the damp-proof course. You could do this yourself, or you could get a professional to do it. 

Tank walls and floors in damp-proof materials

Tanking a wall or floor is a building term that effectively means sealing it to protect it from moisture. This is usually done to areas that are already damp, and might be done by coating the surface in asphalt (a thick liquid) or a membrane. For walls this would be underneath the plaster and for floors it would be under the concrete. The areas have to be prepared first, tanked and then decorated on top, so it's a big job.

Tanking can be very expensive (our costs pages has details) and disruptive, so, like other costly damp work, it's worth getting a few expert opinions to help you decide whether it really is necessary before committing.

If you're looking for a damp specialist, you can use our Which? Trusted Traders website to find recommended tradespeople who have been through our rigorous checks.