The one-table version
| Rising damp | Penetrating damp | Lateral damp | Condensation | |
|---|---|---|---|---|
| Comes from | Groundwater rising | Rain driven through the wall | Soil against the wall | Air inside the room |
| Height | Stops 0.9 – 1.2m up | Any height | Matches the soil line outside | Corners, reveals, cold spots |
| Edge of the patch | Level tide mark | Irregular | Broad and horizontal | Diffuse, spotted |
| Salt bloom | Yes, at the tide line | Sometimes | Often | No |
| Weather | Constant, worse in wet months | Tracks driven rain | Worse after prolonged rain | Worse when closed up and cold |
| Mould | Rare | Sometimes | Sometimes | Almost always, black spotted |
| Treated by | Chemical DPC + replaster | Façade sealing + crack repair | Tanking or drainage | Ventilation and insulation |
Rising damp
Water is drawn up through the masonry by capillary action because the damp-proof course has failed, been bridged, or was never installed. It climbs until the rate of evaporation from the wall face matches the rate of rise, which in most South African construction lands somewhere between 0.9m and 1.2m.
The giveaway is the combination of three things: a reasonably level tide mark, a chalky white salt bloom at that line, and moisture readings that fall as you move up the wall. One of those on its own means very little. Salts without a level line is usually lateral damp; a level line without salts is often just where a previous owner stopped painting.
Treatment is damp proofing in Cape Town — a chemical DPC injected into the mortar bed, followed by hacking off and replacing the salt-contaminated plaster. Skipping the replastering is why so many injections get blamed for failing.
The white band the salts leave on the surface is covered under efflorescence and wall salts.
Penetrating damp
Rain is driven through the wall from outside — through porous plaster, an unsealed hairline crack, eroded pointing, a failed sealant joint around a window, or a combination of all four. It is by a distance the most common damp fault in Cape Town, because our winter rain arrives close to horizontal and finds routes that vertical rain never would.
It presents as an irregular patch at any height, it darkens during and just after a front, and it fades between them. It is almost always worst on the elevation facing the weather — south-west across most of the peninsula.
The fix is on the outside: wall crack repair and façade sealing, then a breathable water repellent across the elevation.
Lateral damp
Soil is retained against a wall — a raised bed, a sloping site, a garage cut into a bank, a planter built against the house — and water moves horizontally out of that soil into the masonry. Because the water arrives with some pressure behind it, this behaves more like a below-ground problem than a wall problem.
It shows as a broad horizontal band whose height matches the soil level on the other side, often with salts, and it does not dry out between rain events the way penetrating damp does.
Coating the inside will not hold it. The answer is either basement and cellar waterproofing applied as tanking, or removing the load with french drains and drainage, and usually both.
Condensation
Warm moist air inside the building meets a cold surface and gives up its moisture there. No water has entered the structure from outside. This is a ventilation and heat problem wearing a damp costume, and it is very commonly misdiagnosed as rising damp because both produce a wet-looking wall.
Tells: black spotted mould rather than staining, worst in corners, behind furniture and around window reveals, worse in winter with the house closed up, no salt band anywhere, and windows that stream in the morning.
No waterproofing system fixes it. Sealing the wall makes it worse by removing the wall's ability to dry inward. What fixes it is extraction at source, ventilation, and dealing with cold bridges.
If a contractor quotes you for DPC injection on a wall with spotted black mould in the corners and no salt band, get a second opinion.
Work through it yourself
The damp diagnosis tool walks the same logic in about thirty seconds, and tells you which system the answer points at.
Common questions
What is the difference between rising damp and penetrating damp?
Rising damp comes up from the ground through the wall and stops at a fairly level line around 0.9–1.2m, leaving a salt bloom. Penetrating damp comes through the wall from outside, appears at any height in an irregular patch, and gets visibly worse during wind-driven rain. If the patch is high on the wall it is not rising damp.
Can you have more than one type of damp at once?
Frequently, and it is a common reason treatments appear to fail. A house with a failed DPC often also has condensation, because damp walls are cold walls. Treating one and not the other leaves the owner convinced the work did not do anything.
How do I know if it is just condensation?
Three checks: is there a white salt bloom anywhere (condensation never produces one), is the mould black and spotted rather than a stain, and is it worse in cold closed-up months rather than after rain. Three yeses and it is condensation.
Does damp go away on its own in summer?
The visible patch often shrinks, which is why people postpone dealing with it. The cause does not go away, the salts stay in the plaster, and the first serious winter front brings it back — usually slightly bigger than last year.