Rising damp: why paint keeps failing at the bottom of the wall
23 June 2026 · 3 min read
A tide mark, blistering at skirting height and salt on the brick. What rising damp actually is, and why painting it is money wasted.
Paint failing in a band along the bottom of a wall, up to about a metre and no higher, is one of the most recognisable faults in older housing. It is also the one most often painted over, repeatedly, at considerable cost.
What is actually happening
Masonry is porous, and water moves up through it by capillary action — the same mechanism that draws water up a paper towel. Ground moisture enters the base of the wall and rises until evaporation from the wall face balances the rate of rise. That equilibrium is what gives the characteristic horizontal tide mark.
Modern buildings have a **damp-proof course**, a physical barrier near the base of the wall. Older Perth housing — pre-war cottages in Bassendean, Guildford, Fremantle, Midland — often has none, or has one that has been bridged or has failed.
Why it destroys coatings
Water is only half the problem. Groundwater carries dissolved salts, and it deposits them in the wall as it evaporates.
Those salts are hygroscopic — they absorb moisture from the air, so the wall stays damp even in dry weather. And they crystallise within the masonry and behind any coating, and crystal growth exerts enough pressure to push a paint film off and to blow the face off the brick.
That is why the failure repeats. The paint is not failing because it was cheap. It is being pushed off from behind by a process that has nothing to do with the paint.
How to tell it apart from other damp
| Sign | Rising damp | Lateral/penetrating damp | Condensation |
|---|---|---|---|
| Position | Band from floor up, level top edge | Patch near the source, any height | Cold surfaces, corners, behind furniture |
| Tide mark | Yes, characteristic | Sometimes | No |
| Salt deposits | Common | Sometimes | No |
| Timing | Persistent year-round | Worse after rain | Worse in winter, worse overnight |
| Smell | Musty, earthy | Musty | Musty, often with mould |
What painting achieves
Nothing durable. A coating over active rising damp will blister, and it will blister faster than the previous one, because you have added another barrier for the salts to build up behind.
The actual remedies
**Find and remove the bridge first.** This is the cheapest fix and it is often the whole problem. Garden beds built up above the damp course, paving laid too high against the wall, render carried down over the DPC, a leaking downpipe at the base of a wall. Correcting ground levels solves a meaningful proportion of suspected rising damp.
**Improve evaporation.** Anything that stops the wall drying — dense cement render at the base, non-breathable paint, a sealed floor covering hard against the wall — makes the tide mark climb. Removing the barrier lets the wall find a lower equilibrium.
**Install a chemical damp course.** Injected cream or fluid that creates a water-repellent barrier in the masonry. A specialist job, and it works where the diagnosis is correct.
**Replaster with a salt-retardant system.** Once the moisture is dealt with, the salts already in the wall have to be managed. Standard plaster over a salt-laden wall will fail again. Salt-retardant renders are formulated to hold them.
Where painting fits
Last. After the water source is fixed, after the wall has been given months to dry, and using a **breathable** system so the wall can continue to release moisture.
A painter who tells you a special paint will fix rising damp is selling you the next failure. The honest answer is that this is a building repair, and painting is what happens after it.