Fixing Damp on a Plastered Wall Before It Spreads

That tide line creeping up from the skirting is not a paint problem. By the time the plaster starts to blow and the salt blooms show, moisture has been sitting in the wall for months. Repainting over it buys you one wet season at best, then the blistering returns and the client calls someone else.

Tell the three damp types apart first

Rising damp shows a fairly even horizontal band, usually under a metre high, with a white salt crust where the water evaporates. Penetrating damp is patchy and follows the weather: it grows after a downpour and dries back in a dry spell. A bridged damp course looks like rising damp but stops abruptly where a paving slab or garden bed was built up against the wall above the original course.

Before you quote anything, run a hose test on the outside face for twenty minutes and take moisture readings inside at three heights. If the reading climbs only after the hose runs, you are chasing a leak or a bridge, not the ground. That single test saves you from stripping plaster that was never the problem.

The repair sequence that actually holds

Once the source is fixed and the wall has had time to dry, the work runs in a fixed order. Skip a step and the damp comes back through the new finish.

• Strip all compromised plaster back to sound masonry, at least 300 mm past the visible damp edge.
• Treat the exposed brick or block with a salt-neutralising wash and let it dry fully.
• Re-render with a breathable mix; a waterproof additive on a damp wall traps moisture instead of releasing it.
• Allow the render to cure before painting, then use a breathable masonry paint rather than a sealed acrylic.

Coastal humidity versus inland winters

In Durban the wall may never fully dry between rain spells, so drying times stretch and you need to plan the render around the weather. Inland, the dry winter works in your favour, but the same dryness can shrink fresh render too fast and cause hairline cracks. A plasterer charging per square metre should be quoting the drying and curing time into the job, not just the trowel work.

When to call an engineer

If the damp sits above a lintel, follows a diagonal crack, or the floor near the wall has dropped, stop. That is a structural question, not a handyman job, and no amount of render will fix a failing foundation or a settled footing.