Rising Damp
Damp, salty, crumbling brickwork at the base of a wall — rising damp is an old-building problem that needs an old-building fix.
Rising damp is groundwater moving up through masonry by capillary action, carrying salts that crystallise and break down bricks and mortar. It is common in pre-1930 Sydney buildings with failed or missing damp-proof courses. The correct fix is injecting a new chemical damp-proof course, removing impermeable modern render and paint, and re-rendering with breathable lime-based materials. Cement render and waterproof paint make rising damp worse, not better. Romans Building Services assesses rising damp across Sydney before recommending repair, so the visible damage and the cause are both dealt with.
Last updated: 2026-05-29
What is rising damp?
Rising damp is when moisture from the ground moves up through masonry by capillary action — the same way a paper towel soaks up water. It carries dissolved salts with it, and when the moisture evaporates at the wall surface, the salts crystallise and expand, breaking down the mortar and brick faces. Over years it produces the classic tidemark a metre or so above floor level, with salt-crusted, crumbling brickwork below.
Older Sydney buildings — pre-1930, often pre-1910 — frequently have rising damp because they were built before damp-proof courses were standard. Or the original damp course has degraded. Modern fixes often make it worse: cement render and waterproof paint trap the moisture against the wall, accelerating the decay.
Proper treatment is about letting the wall breathe while managing the moisture source. That means breathable lime mortars and renders, not modern cement-based products. The fix takes patience, but it holds.
Signs to look for
- Tidemark or staining about 1m up from floor level
- Salt efflorescence (white fluffy crystals) on the wall surface
- Paint or render bubbling, flaking or falling off in the affected zone
- Mortar crumbling when you scratch it with a key
- Musty smell in rooms with affected walls
- Damp patches at the base of internal walls
- Timber skirting boards rotting or warping
Why it happens
- No damp-proof course in original construction (common pre-1930)
- Damp-proof course that has failed over time
- External ground levels raised above the damp course over the decades
- Poor drainage against external walls
- Impermeable modern render trapping ground moisture in the wall
- Leaking underground pipes or stormwater
How urgent is this?
Rising damp is rarely an emergency but it never stops on its own, and left for years it seriously damages brickwork and internal finishes. The longer you leave it, the bigger the repair scope when you get around to it. If timber skirtings or floorboards are rotting, move it up the list.
How we fix it properly
Confirm it is actually rising damp
Rising damp is often misdiagnosed. Penetrating damp, condensation, leaking pipes and bridged damp courses all look similar. We test moisture levels and salt profiles to confirm before spending money on the wrong treatment.
Remove failed modern materials
Cement render, waterproof paint, vinyl wallpaper — anything impermeable in the damp zone comes off. These are what cause the damp to spread and build up salts.
Install a new damp-proof course
For older buildings we typically inject a chemical DPC — silane or siloxane cream injected into the mortar bed at ground level. Cures and forms a water-repellent barrier. For heritage work with lime mortar, we match the DPC system to the wall.
Re-render with breathable lime
Lime-based render and plaster let the wall dry out instead of trapping moisture. This is the opposite of modern cement render. It takes longer to cure but the wall breathes the way it was designed to.
Address the ground and drainage
Lower garden beds and paving so they are below the damp course. Re-direct stormwater away from the wall. Without this the new damp course will eventually be bridged again.
Typical cost range
$3,500 – $15,000 for typical domestic rising damp treatment per wall, depending on length and whether internal finishes also need redoing.
Every job is different. We give a firm quote after inspection.
Common questions
How do I know if it is rising damp or something else?
Rising damp has a classic tidemark — a horizontal stain line, usually about 1m above floor level. It is worse at the bottom and tapers off above. Penetrating damp has isolated patches tied to a specific leak point. Condensation is usually on cold surfaces and windows. We do moisture and salt testing to confirm before treatment.
Will painting the inside wall fix the damp?
No — and waterproof paint will make it worse by trapping moisture. Paint is a finishing step after the damp course, render and drainage are sorted. Painting without those other steps fails in months.
Does my heritage building need special treatment?
Yes. Heritage buildings need breathable lime-based systems, not modern cement. Using cement render on an old soft brick wall traps moisture and accelerates damage. We match the system to the age and fabric of the building.
How long does a chemical damp course last?
Properly injected chemical DPCs typically carry a 20 to 30 year manufacturer warranty. The render and surface finishes need to be done right alongside it — the DPC on its own is not the whole fix.
Services that fix this
Rising Damp in your area
The causes and right fix for rising damp vary with local housing stock and exposure. Read the version closest to where you are:
Where we see rising damp most often
Some suburbs have more of this problem than others — the local housing stock, age, and coastal exposure all play a part. Click through for the local context.
Think you might have rising damp?
Send a photo or call Minas directly. We will tell you straight whether it needs doing now, or whether it can wait.