Rising damp or a leak? How to tell the difference yourself

It starts near the skirting. A patch that looks slightly darker, then a bubble, then the paint comes away in a sheet with a bloom of white powder behind it. You scraped it, you sealed it, you painted it, and by the following July it was back in the same place, slightly bigger.

Somebody has probably told you it is rising damp. That is the phrase everybody reaches for, and it is the single most over-diagnosed condition in South African housing. In our experience most walls blamed on rising damp are actually something else, and the something else is usually cheaper to fix.

You can narrow it down yourself in about twenty minutes with your eyes, your hand, and a piece of tape.

Read those four carefully and you will notice that the two questions doing most of the work are: does it change with the rain, and is there salt or mould on it. Between them, they sort most walls.

1. 1Height and shape. Rising damp is low and level. A patch that starts at head height, or has a random shape, is not rising damp.
2. 2Salt or mould. Wipe the bloom. A gritty white crystalline deposit means salts carried out of the masonry by moisture, which points to rising or penetrating damp. Black fuzzy growth means condensation.
3. 3The weather test. Keep a note for a month. Does it darken within a day or two of rain and fade in a dry week? That is penetrating damp. Is it constant regardless? Rising damp or plumbing.
4. 4The tape test for condensation. Tape a square of clear plastic tightly to the wall. Come back after two days. Water on the room side of the plastic means condensation. A damp wall under the plastic, dry plastic, means moisture coming out of the wall.
5. 5Go outside and look at the same spot. This is the step almost everybody skips and it solves most cases. Is the garden bed built up against that wall above floor level? Is there a downpipe discharging next to it? Is the paving sloping towards the house? Is there a leaking gutter joint directly above? Is the wall plaster bridging the damp course?
6. 6Check the plumbing. Close every tap in the house and read the water meter. Come back an hour later. If it has moved, you have a leak, and no amount of waterproofing will help.

• Did the contractor go outside and look at the ground level, paving falls, downpipes and gutters on the other side of that wall? If not, they have not diagnosed anything.
• Did they take a moisture reading in more than one place, at more than one height, and write the numbers down?
• Did they ask you whether it changes with the weather?
• Did anybody check the plumbing?
• Is the proposed work aimed at the source of the water, or only at the appearance of the wall?
• If the recommendation is to strip and re-plaster inside, has anybody explained why the water will not simply come back through the new plaster?

One thing worth saying plainly. A damp wall needs to dry before it gets painted, and that takes weeks, not days, in a Cape winter. Any contractor who is happy to skim and paint a wet wall next Tuesday is selling you a repeat of the same problem.

Fix the water, then wait, then paint. In that order, or you will do all three again.

We take moisture readings at several heights, look at the outside face of that wall properly, check ground levels, paving falls, downpipes and gutters, and ask you how it behaves through the seasons. Then you get a written diagnosis naming the mechanism.

If the answer is drainage or plumbing, we tell you and we do not sell you a coating. If the answer is a surface letting water in, we specify Rubber Sealant liquid rubber on that surface and its details, from R290 per square metre, and we tell you how long the wall must dry before the interior can be repainted.