Rising Damp Has a Ceiling Height
Water moves up through masonry by capillary action, the same way it moves up a paper towel dipped in a glass. That process has a limit, because gravity eventually balances the capillary pull.
In practice that limit is around a metre, sometimes a little more in very fine-pored materials, sometimes less. It is not a rule invented by anyone, it is physics.
So if the damp on your wall reaches 1.5 metres, or appears on the first floor, or shows in a patch in the middle of a wall with dry brickwork below it, it is not rising damp. Whatever is causing it, the ground is not.
That one test eliminates the majority of walls we are called to look at for rising damp, before any equipment comes out of the van.
What Genuine Rising Damp Looks Like
A tide mark. A reasonably horizontal line where the water stops, often with a band of staining or salt crystallisation just below it.
Salt deposits. Groundwater carries dissolved salts. The water evaporates from the wall surface and leaves the salts behind as a white, fluffy or crystalline bloom, called efflorescence. Those salts are hygroscopic, meaning they attract moisture from the air, so contaminated plaster stays damp even after the source is stopped.
Damage at skirting level. Perished skirtings, lifting floor coverings, blown plaster at the base of the wall.
Consistency. It does not come and go with the weather the way penetrating damp does, and it is not confined to cold surfaces the way condensation is.
No damp proof course, or a bridged one. Which brings us to the thing we check before anything else.
Check for a Bridge Before You Inject
A large share of the genuine rising damp we find is not a failed DPC. It is a perfectly good DPC that has been bypassed.
Raised ground levels. A patio, driveway, paving or garden bed built up against the wall above the level of the DPC. Water enters the wall above the barrier and rises from there. Extremely common after landscaping or a new paved area.
Internal screeds poured over the DPC in a renovation.
Debris in a cavity wall bridging from the outer leaf to the inner.
Render carried down across the DPC line on the outside face.
Fixing a bridge means lowering ground levels or cutting a channel, and it is far cheaper than injecting a wall. We look for it first, every time.
Old Cape Town Walls and Sea Sand
Much of Cape Town older housing stock, the City Bowl cottages, Woodstock, Observatory, the older southern suburbs, was built before damp proof courses were standard. Solid masonry walls, no barrier, in some cases on damp ground.
There is a second, local complication. Older Cape Town plaster was frequently mixed with beach sand, which was locally available and free. Sea sand carries chlorides. Those salts sit in the plaster permanently and are strongly hygroscopic, so they pull moisture out of humid air and hold it in the wall surface.
The practical consequence is that in these buildings, injecting a DPC without replacing the contaminated plaster achieves very little visible improvement. The wall stops wicking from the ground and carries on looking damp, because the plaster itself is now the moisture source. Re-plastering with a salt-retardant system is not an optional extra on those walls, it is the treatment.
