Telling them apart
| Rising damp | Penetrating damp | Condensation | |
|---|---|---|---|
| Height | Stops 0.9 – 1.2m up | Any height, often high | Corners, reveals, cold spots |
| Edge | Level tide mark | Irregular patch | Diffuse, spotted |
| Salt bloom | Yes, at the tide line | Sometimes | No |
| Weather link | Worse in wet season, always present | Tracks wind-driven rain | Worse in cold, closed-up months |
| Mould | Rare | Sometimes | Almost always, black spotted |
| Treatment | Chemical DPC + replaster | External sealing + crack repair | Ventilation + insulation |
| Indicative | R450 – R850/lin m | R180 – R450/lin m | Often no contractor needed |
Rising damp — what the treatment involves
- Confirm it with a moisture meter at multiple heights, and confirm the salt band. A level tide mark plus salts is rising damp; without both, keep looking.
- Drill a horizontal course of holes into the mortar bed, typically 10–12mm at 100–120mm centres, as close to floor level as the construction allows.
- Inject a silane/siloxane DPC cream or fluid until the course is saturated, forming a continuous horizontal barrier.
- Hack off the contaminated plaster to at least 300mm above the highest tide mark — usually to 1m — because the salts in that plaster are hygroscopic and will keep pulling moisture from the air forever if left.
- Re-render with a salt-inhibiting mix, skim, and leave it to dry before painting. A wall dries at roughly 25mm of thickness per month.
Injection alone is half a job. If the salt-contaminated plaster stays on the wall, the damp patch comes back and the DPC gets blamed.
Penetrating and lateral damp
This is the most common damp fault in Cape Town, because our rain arrives sideways. Water is driven through porous plaster, an unsealed hairline crack, failed pointing or a perished sealant joint, and shows up as an irregular patch that darkens during a front and fades between them.
The fix is on the outside, not the inside: rout and seal the cracks, make good the plaster, and apply a breathable silane water repellent that stops liquid water entering while still letting the wall dry outward.
Do not seal a damp wall with a non-breathable coating. You trap the moisture inside the wall, and the next thing that happens is the plaster blows off in sheets.
Condensation — when you do not need a contractor
If the mould is black and spotted, sits in corners and around window reveals, is worse in winter with the windows closed, and there is no salt band, it is condensation. No waterproofing system fixes it, and sealing the wall makes it worse by removing the wall's ability to dry.
What fixes it is ventilation, extraction at the source, and dealing with cold bridges. We will tell you when that is what you have.
Common questions
How much does damp proofing cost in Cape Town?
Chemical DPC injection for rising damp runs about R450–R850 per linear metre. Salt-retardant replastering afterwards is about R280–R480 per m². External sealing for penetrating damp runs about R180–R450 per linear metre of crack, plus the coating.
How long does a wall take to dry after damp proofing?
Roughly one month per 25mm of wall thickness, so a 230mm solid wall takes the better part of a year to fully dry. It can be plastered and painted well before that with the correct salt-inhibiting render, but do not expect an instant result.
Does damp proof paint work?
On rising damp, no. It seals the surface, the moisture continues rising behind it, and the paint blows off along with the plaster. It has legitimate uses as part of a specified system, but it is not a treatment for a wall that is drawing water from the ground.
Is rising damp even real?
It is real but it is over-diagnosed, which is where the scepticism comes from. Genuine rising damp needs a level tide mark, hygroscopic salts at that line, and elevated moisture readings that fall as you go up the wall. Absent all three, look for another cause first.