Rising damp and mould in Australian homes: a guide

Published by Aurala Naturals. Last updated 2026.

Rising damp is groundwater soaking up through brick and mortar from the ground, usually where the damp-proof course has failed or was never installed. It leaves a tide mark and flaking, salty paint low on the wall, and it feeds mould along the base that keeps coming back until the moisture is fixed.

What is rising damp in Australian homes?

Rising damp is groundwater moving upward through the solid parts of a wall. Brick, mortar and stone are full of tiny pores, so a wall behaves a little like the bottom of a paper towel dipped in a puddle: water is drawn up through the narrow channels by capillary action. In most homes there is meant to be a damp-proof course, a waterproof barrier built into the wall close to ground level to stop that wicking. In older Australian houses the barrier may never have been fitted, or after a hundred years it can crack, break down, or get bridged by render, a garden bed or a raised path. It is especially common in older brick and stone homes, including many Federation and Victorian-era terraces where a modern barrier was never part of the build. Once the barrier is out of action, the ground feeds moisture into the wall day after day. The water usually climbs somewhere between half a metre and a metre before evaporation and gravity cancel out the upward pull, which is why the damage sits low. Rising damp is one of several moisture faults behind what causes mould in Australian homes, and it is one of the most stubborn because the supply of water never stops on its own.

How can I tell if a wall has rising damp?

Rising damp leaves a fairly consistent set of marks, always low on the wall and usually at a steady height along its length. If the damage is up high, in corners or around windows, the cause is more likely something else. Look for these signs near the base of an affected wall:

• A horizontal tide mark, often yellow, brown or grey, roughly half a metre to a metre up from the floor.
• A white, powdery, crystalline crust on the brick or plaster, known as efflorescence, which is salt left behind as the water evaporates.
• Paint that bubbles, flakes or lifts, and plaster that feels soft or crumbles.
• Mortar that has gone sandy and loose between the bricks.
• Skirting boards that are swollen, and a damp, musty patch that lingers at floor level.

The salts are a useful giveaway. They are carried up out of the ground and the mortar by the water, then deposited on the surface, so they point clearly to a ground source rather than moisture from the air. The height staying level along the whole wall is the other strong clue, and it is worth measuring the band before you decide on a cause.

How is rising damp different from condensation?

The quickest way to separate the two is to ask where the water comes from. Rising damp comes from the ground and moves up into the wall through the masonry. Condensation comes from the air: warm, moist indoor air touches a cold surface, cools past its dew point, and the water it was holding turns back into liquid on that surface. Because the sources are different, the patterns are different. Rising damp sits low and holds a steady height. Condensation shows up on the coldest surfaces, so you see it on windows, in ceiling corners, on outside-facing walls and behind wardrobes pushed against cold brick, often well above floor level. Rising damp brings salts to the surface; condensation does not. If the marks are high, patchy and worst in the cold months on cold spots, you are probably looking at a condensation problem, which is covered in our note on condensation, dew point and mould. A home can have both at once, which is why it pays to read the position and the salts rather than guess.

Why does the mould keep coming back along the base of the wall?

Mould grows wherever there is moisture and something to feed on, and a rising-damp wall offers both without a break. The plaster, the paint, the paper backing and the everyday dust in the room are all food. The water is topped up from the ground continuously, so even after you wipe the surface clean the wall stays wet underneath and the growth simply returns. This is the core reason surface cleaning alone never holds: you are removing the visible layer while the conditions that grew it are untouched. The salts make it worse, because many of them are hygroscopic, meaning they pull moisture out of the air and keep the wall face damp even on drier days. If you want the underlying picture of why a damp, fed surface colonises so readily, our explainer on how mould actually grows and spreads walks through it. Along a rising-damp wall the mould is a symptom, and it will keep returning for as long as the wall keeps drinking from the ground.

What should I do about rising damp and the mould it causes?

The real fix is to stop the water, and that is a job for the fabric of the building rather than a spray bottle. A qualified damp specialist or builder can confirm the diagnosis and put in a working barrier, and there are usually a few external causes to correct at the same time. Typical steps include:

• Installing a new damp-proof course, often by injecting a water-repellent cream into a line of holes drilled along the mortar.
• Lowering garden beds, paths or paving that have built up above the original barrier and are letting water bridge across it.
• Clearing and reopening blocked subfloor vents so the space under the floor can dry out.
• Fixing drainage, leaking downpipes and beds that channel water against the wall.
• Removing and replacing salt-contaminated plaster once the wall has dried, because old salts keep drawing damp back.

Be honest with yourself about the order of work. No cleaner and no coating removes rising damp on its own, and anything that promises to seal the problem away without addressing the ground water tends to trap moisture and push the damage sideways. Fix the source first, then deal with what is left on the surface.

Can I manage the surface mould while the damp is being fixed?

Yes. Damp-proofing can take time to arrange and then time for the wall to dry, so keeping the visible mould in check in the meantime is reasonable, as long as you treat it as maintenance, not a one-off fix. Wipe affected areas regularly, keep the room as ventilated as you can, and avoid pushing furniture hard against the wall so air can move across it. Once you have wiped a surface clean, a plant-based way to help it stay clear is our own blend, First Light mould defence, a six-oil essential-oil mix made in Australia for routine upkeep on hard surfaces you have already cleaned, to help stop mould resettling. It is not a cleaner: mist a few drops in water lightly over the clean surface, or diffuse it in the room. Lab tested: 99.2% reduction in black mould on direct contact, measured by an independent laboratory. Use it the sensible way with any essential-oil product: dilute as directed, work in a ventilated room, spot-test a small hidden patch first, and keep the concentrate away from pets and children. None of this replaces the damp-proofing. Think of surface care as holding the line so the wall looks and stays cleaner while the moisture fix does the lasting work.

Rising damp is a moisture problem first and a mould problem second, so start by reading the wall: check the height, look for the tide mark and the salts, and get the ground water diagnosed. Sort the source, keep the surface in check, and the base of that wall can finally stay clear.

Common questions

How high does rising damp usually climb? On most walls rising damp reaches somewhere between half a metre and a metre above floor level before evaporation balances the upward pull. The height tends to stay fairly even along the wall. If damp or mould sits well above that band, or only in corners and around windows, the cause is more likely condensation or a leak rather than groundwater.

Is the white powder on my wall a sign of rising damp? Often, yes. That white, crystalline crust is efflorescence, salt carried up out of the ground and the mortar by the water and left behind as it evaporates at the surface. It points to a ground source rather than moisture from the air. The salts also hold damp, which is one reason mould keeps returning along the base of the wall.

Will cleaning the mould off stop it coming back? Not on a rising-damp wall. Cleaning removes the visible growth but leaves the wall wet underneath, because the ground keeps topping up the moisture, so the mould simply returns. Surface care keeps things tidier in the short term, but the growth only settles once the damp-proofing fixes the water supply and the wall is allowed to dry out and stay dry.

Can I fix rising damp myself? The surface mould you can manage yourself with regular wiping and good ventilation, but the damp itself is usually a job for a qualified specialist. Installing a new damp-proof course, lowering built-up garden beds and paths, and reopening blocked subfloor vents are the steps that stop the water. Getting the diagnosis right first saves money, because treating the wrong cause rarely holds.