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Diagnose damp and root it out

Damp is one of the most worrying conditions for a home owner. You often fear the worst and you’re not sure whether to opt for a Band Aid or for a more radical cure like chopping open the walls.

The first thing to do is to try to understand the cause of the damp, according to John Graham, CEO of HouseCheck. Often this is best done by employing a home inspector or a water-proofing expert to check out the problem. But for those home owners who want to try a spot of self-diagnosis, here’s some information which will help you.

There can be various manifestations of damp in a home – all caused by moisture penetration. With all types of damp, damaged areas should only be repaired and decorated once there is certainty that the source of the moisture ingress has been repaired and the damaged area has completely dried out.

Penetrating damp

Penetrating damp is usually caused by roof leaks or water ingress via exterior wall cracks. Other causes may be leaking plumbing, adjacent the shower or the bath, a planter on an external wall or water penetrating the exterior skin of a cavity wall as a result of incorrect exterior ground levels. Further investigation is always recommended. 

Rising damp

Rising damp is confined to the lower parts of internal walls. Rising damp is caused by ground water “wicking up” through the masonry due to the lack of (or damaged) damp proof course (DPC).

Rising damp is often found in older buildings because modern DPC was not available when these old buildings were erected. Malthoid (flexible bitumen-coated felt), or slate, was used in these times to prevent rising damp. However, these components usually disintegrate over time and this then allows moisture from the soil to rise up through the walls. It is recommended that a reputable waterproofing company be contracted to evaluate and investigate thoroughly, and then to propose best solutions to repair the rising damp. This may involve installing a chemical damp-proof barrier or removing bricks to install a physical DPC.


Efflorescence is an aesthetic problem at first. Efflorescence is a white, powdery salt substance that forms on the surfaces of concrete, bricks and plaster. It is caused by soluble salts migrating through the material via capillary action. Once these soluble salts come into contact with air, unsightly white sediment appears.

Efflorescence is often found on new brickwork and may just be an indication that there is moisture in the mortar and bricks. Efflorescence in older walls is evidence of a more serious problem – either penetrating damp or rising damp. In this case the cause of the moisture penetration needs to be established and resolved.

In severe cases plaster contaminated with efflorescent salts needs to be removed and replaced to prevent damp to newly painted wall surfaces.


Black mould is actually colonies of fungal spores which grow on walls and ceiling in damp conditions. These mould spores can be dangerous to people with allergies.

Again the cause of the damp conditions must be established to satisfactorily resolve the problem.

In bathrooms and bedrooms the cause is very often poor ventilation resulting from people showering or sleeping with the closed windows (it’s amazing how much moist, warm air a sleeping human being can produce). If this is the case, the solution is to regularly open some windows to create cross ventilation in the room, or perhaps to install an extractor fan.

Mould can also be an indicator of penetrating damp – from roof leaks or leaking water pipes inside the walls or ceilings.

Once the cause of the mould has been established and eliminated, the mould spores are easily removed with a mild bleach solution prior to repainting.

Who is John Graham?

John Graham, founder and CEO of HouseCheck.

John Graham, founder and CEO of HouseCheck.

John Graham is a South African who has spent more than 30 years in the property industry. He has hands-on experience as a developer, investor, estate agent, home builder and property inspector. John is the founder and CEO of HouseCheck (www.housecheck.co.za) and the principal of the SA Home Inspection Training Academy (www.sahita.co.za). He is the author of a number of popular eBooks including: The South African Home Buyer’s GuideQuality Control for South African Home Building and The Complete Guide to South African Home Inspection.


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