There Are Three Kinds of Damp
They look similar on a wall and they have almost nothing in common underneath.
Rising damp comes up from the ground through the wall by capillary action, where there is no damp proof course or the existing one has been bridged or has failed. It is genuinely uncommon compared to how often it is diagnosed.
Penetrating damp comes in horizontally through the wall from outside. A failed gutter, a cracked render, a defective flashing, a leaking pipe, a wall that faces the winter rain. Water gets in somewhere specific and shows up inside.
Condensation is not water coming in at all. It is water already in the air inside the house, condensing on cold surfaces. In Cape Town it is by far the most common of the three and the most frequently misdiagnosed.
The treatments are completely different, and expensive, and none of them work on the wrong problem. This is why we diagnose before quoting rather than arriving with a solution already chosen.
Most Damp Treated as Rising Damp Is Not
The commercial pressure in this trade runs one way. Chemical damp proof course injection is a well-defined, sellable product with a clear price, and it can be quoted from a doorstep in ten minutes.
Condensation, by contrast, is a diagnosis that leads to ventilation advice, heating advice and maybe some insulation. Much harder to sell and much less profitable.
So the wall gets injected, the plaster gets replaced, and the damp comes back, because the wall was never wicking water up from the ground.
How to tell them apart:
Height. Rising damp is limited by how far water can wick against gravity, which in practice is roughly a metre. Damp above that height, on an upper floor, or in the middle of a wall, is not rising damp.
A tide mark. Genuine rising damp usually leaves a horizontal line where the water stops, often with salt staining along it.
Pattern. Condensation appears on the coldest surfaces first: external corners, behind furniture, on window reveals, in unheated rooms. It is worse in winter and worse in bedrooms and bathrooms.
Season and behaviour. Penetrating damp appears during and after rain and is often worse on the weather-facing wall. Condensation is worse on cold mornings and when the house has been shut up.
Mould. Black spot mould is a condensation signature. Rising damp produces salt deposits and staining rather than black mould.
What We Find Outside
A large share of damp diagnosed indoors is caused by something obvious outside, and it is usually cheaper to fix than any damp treatment.
Blocked or broken gutters discharging down a wall. The single most common cause of penetrating damp we see, and a gutter repair rather than a damp job.
Ground levels raised above the damp proof course. A new paved patio, a raised flower bed or a screed laid against the wall bridges the DPC and lets water in above it.
Cracked or blown render, which lets water in and then holds it against the brickwork.
Failed pointing in older masonry.
Leaking downpipes and gullies, saturating the base of a wall continuously.
We look outside before recommending anything invasive inside.
Why Cape Town Gets This Wrong
Two local conditions drive the misdiagnosis.
No central heating. Almost no Cape Town homes have it. Through a wet winter, a house is heated intermittently by portable heaters, windows stay shut against the rain, and moisture from cooking, washing and drying clothes indoors has nowhere to go. It condenses on cold external walls. This is a heating and ventilation problem presenting as a damp problem.
Old solid-wall stock with no DPC. Much of the older housing in the City Bowl, Woodstock, Observatory and the older southern suburbs predates damp proof courses entirely. In those buildings genuine rising damp does exist, and it is compounded by sea sand having been used in the original plaster, which brings hygroscopic salts that pull moisture from the air permanently.
So Cape Town has both the most over-diagnosed cause and a real reservoir of the genuine article. Telling them apart is the job.
