Rising damp is ground moisture drawn up through the bricks and mortar of a wall where there is no working damp proof course. It usually shows as a tide mark up to around a metre above the floor, white powdery salts and plaster that has gone soft or blown. Treatment starts with confirming the diagnosis, because many low-level damp problems are caused by something else, and then removing the cause: clearing a bridged damp proof course, injecting a new one where needed, and replacing salt-contaminated plaster.
What does rising damp actually look like?
True rising damp has a fairly recognisable pattern. The damp sits at the bottom of the wall and fades out at a reasonably even height, usually somewhere below about a metre. Above the wet band there is often a brown or yellowish tide line where dissolved salts have been left behind as water evaporated. Skirting boards may feel soft or show signs of rot, paint and paper lift at the bottom of the wall, and the plaster can sound hollow when tapped.
- A horizontal band of damp or staining starting at floor level
- White, fluffy or crystalline salt deposits on the plaster surface
- Plaster that crumbles, bubbles or comes away low on the wall
- Damp that stays fairly constant through the year rather than coming and going with rain
- Rotting skirting boards or a musty smell near the floor
Black mould is not usually a sign of rising damp on its own. Ground salts tend to discourage mould, so black spotting in corners, behind furniture or around windows points more towards condensation. Our damp and mould problems guide compares the patterns side by side.
Why is rising damp so often misdiagnosed?
Rising damp is one of the most over-diagnosed problems in British homes. A wall can be wet at low level for several reasons that have nothing to do with a failed damp proof course, and an injected chemical barrier will not help any of them.
| What you see | Possible cause | What usually fixes it |
|---|---|---|
| Damp low on an outside wall, worse after rain | Splashback, a leaking downpipe or gully, or water running down the wall | Repair the rainwater goods or drainage outside |
| Damp band with soil or a path higher than the inside floor | A bridged damp proof course | Lowering ground levels or cutting back render so the original DPC works again |
| Damp in one spot near a kitchen or bathroom | A leaking pipe, waste or appliance hose | Find and repair the leak, then let the wall dry |
| Wet patches and mould in cold corners, worse in winter | Condensation | Better ventilation and steadier heating |
| Even tide mark, salts, damp all year | Rising damp | A new damp proof course plus replastering |
Damp meters add to the confusion. The common pin-type meter is designed for timber, and on plaster and brick it gives relative readings that are thrown off by salts, foil-backed wallpaper and surface condensation. A high reading low on a wall shows something is there, but not what. Proper diagnosis looks at the pattern, the building and the outside ground levels, and where it matters, uses more reliable tests such as drilled samples analysed with the calcium carbide method.
How do we diagnose rising damp?
BS 6576:2005+A1:2012, the British Standard code of practice for diagnosing rising damp and installing chemical damp-proof courses, sets out a careful approach rather than a quick meter reading. We follow the same logic on every visit.
- Talk it through. We ask how long the damp has been there, whether it changes with the weather or the seasons, and what work has been done to the house before.
- Look at the whole wall. We check the height and shape of the damp band, look for salts, and see whether the problem is on outside walls, party walls or internal walls.
- Check outside. We look at path and garden levels against the DPC line, render or pointing taken down over it, downpipes, gullies and leaks.
- Take readings and samples where needed. Moisture and humidity readings help rule condensation in or out; samples give a better picture of moisture deep in the wall.
- Explain and quote. We explain in plain English what we found and give a written quote for the work that matches the cause.
What does rising damp treatment involve?
Where an existing damp proof course has simply been bridged, the first job is to stop the bridge. That might mean lowering a raised path or flower bed, cutting back render that has been run down to the ground, or clearing debris. It is often the least disruptive fix and sometimes the only one needed.
Where there is genuinely no working DPC, a new barrier is formed. The usual method today is a silicone-based cream injected into a line of holes drilled along a mortar course, which spreads into the mortar and forms a water-repellent layer. Our page on damp proof course injection explains that part of the job step by step.
Injection is only half of it. Plaster that has been wet for years is usually loaded with hygroscopic salts that pull moisture from the air, so even with a new DPC the old plaster can stay damp. The affected plaster is normally hacked off and replaced with a salt-resistant system, as described on our replastering after damp page. Skirting boards and any rotten timber are renewed at the same time.
Liverpool homes and rising damp
Much of Liverpool's older housing is solid nine-inch brick with no cavity, built before modern damp proofing was standard or with early slate or bitumen courses that may now be failing. Long Victorian and Edwardian terraces in areas such as Anfield, Walton and Kensington often have yards and paths that have been raised over the decades, back extensions added at different times and front walls rendered down to the pavement. Those are exactly the details that bridge a damp proof course. We see plenty of genuine rising damp in these streets too, which is why the diagnosis matters before money is spent.
As part of our wider damp and mould treatment in Liverpool, we look at the whole house, not just the patch you called about. Low-level damp, condensation and a leaking gutter can all be present at once, and each needs its own fix.
What affects the cost of rising damp treatment?
We do not publish set prices because every wall is different. The main factors are the length of wall affected, the wall thickness, whether the existing DPC can be restored by removing a bridge, how much plaster needs replacing, access (fitted kitchens, built-in units, stairs), and whether skirting boards or floor timbers need renewing. Drying time and redecoration also need planning. The damp and mould cost guide lists published national figures for comparison.
If the house has textured ceiling or wall coatings, or old boards, and was built or refurbished before 2000, these may contain asbestos. We do not disturb suspected asbestos; it has to be tested by a licensed specialist first.
Worried you have rising damp?
Call 07777 659786 or use the form. Tell us which walls are affected and how long it has been going on, and we will call you back to arrange a visit. As a local damp specialist in Liverpool, we will tell you honestly if it turns out to be something simpler.
Frequently asked questions
How do I know if it is rising damp or condensation?
Rising damp usually forms a band at the bottom of the wall with salts and a tide mark, and stays fairly constant all year. Condensation tends to show as black mould in corners, behind furniture and around windows, and gets worse in cold weather when the heating is low and windows are shut. It is common to have both, which is why we look at the pattern rather than relying on a meter reading.
Can rising damp be fixed without injecting a new damp proof course?
Often, yes. If the original damp proof course has been bridged by raised ground, a path, render or debris, removing the bridge can let it work again. Fixing a leaking downpipe or gully near the wall can also clear what looks like rising damp. We only recommend injection where there is no effective DPC left.
How long does rising damp treatment take?
The injection and replastering for a typical room usually take a few days, depending on how much wall is affected and access. The wall then needs time to dry before final decoration, which is usually several weeks and can be longer in winter or on thick solid walls.
Does rising damp cause black mould?
Not usually on its own. The salts carried up by rising damp tend to discourage mould growth. Black mould is far more often caused by condensation or by a leak keeping a surface wet. If you have both tide marks and mould, there may be two problems to deal with.
Is rising damp the landlord’s responsibility?
In most private tenancies, the landlord is responsible for keeping the structure and exterior of the home in repair, which normally includes damp proofing. Tenants should report it in writing. We can provide written notes and photos that a landlord or agent can use; for legal questions, speak to the council or Shelter.
Will a dehumidifier cure rising damp?
No. A dehumidifier dries the air in the room and can help with condensation, but it will not stop moisture coming up through the wall from the ground. It can be useful while new plaster dries out after treatment, but the source of the damp still has to be dealt with.