Damp proofing
Damp proofing means stopping water getting into a building from the ground, or keeping it out of rooms below ground. It can be a new damp proof course, a membrane, tanking a cellar, or replastering a salt-damaged wall. It is the right answer to some damp problems and the wrong one to many others.
We don't do damp proofing. We pass your enquiry to one independent specialist near you, who looks at the problem and quotes you directly. Free, no obligation.
What damp proofing covers
- Chemical damp proof course. A cream or fluid injected into a line of holes drilled along the mortar, low down in the wall. It sets as a water-repellent band. This is the most common treatment sold for rising damp.
- Physical damp proof course. A strip of membrane or slate built into a slot cut through the wall. Slower and dearer, and less common in existing homes.
- Damp proof membranes. Sheets fixed to a wall or laid under a floor to keep moisture away from the surface. Used where a wall stays damp, or after a floor is dug out.
- Tanking. Waterproofing a cellar or basement so it can be used, with a cementitious coating or a cavity drain membrane and a pump.
- Replastering. Taking off plaster that's full of salts and putting back a plaster that copes with them. Often done alongside a new damp course, and sometimes the bit that actually solves the problem.
When it's the wrong fix
A lot of damp proofing is sold to houses that don't need it. Before you pay for any treatment, make sure the specialist has looked at:
- condensation, which causes most mould inside homes and has nothing to do with the damp course
- gutters, downpipes, pointing and render, which let rain into walls
- ground or paving outside that sits higher than the existing damp course, which lets water bypass it
- plumbing leaks under floors and inside walls
- air bricks that have been blocked, which can lead to damp under suspended timber floors
Older homes, especially those built before cavity walls became usual between the wars, tend to have solid brick or stone walls that were designed to take on some moisture and let it dry out. Sealing them with cement render or plastic paint can make damp worse. A specialist who knows older buildings will talk about this; one who doesn't may go straight to the drill.
What a good specialist will do
- Look outside before they look inside.
- Use a moisture meter as a guide, not a verdict. Meters read high on salty plaster even when the wall itself is drying.
- Explain the cause in plain words and say what else they've ruled out.
- Give a written quote that separates the cause from the cosmetic work, and says what the guarantee covers.
What it usually costs
| Job | Typical range | Source |
|---|---|---|
| Chemical damp proof course, per metre of wall | £60–£200 | Checkatrade |
| Chemical damp proof course, per metre of wall | £60–£90 | MyJobQuote |
| Injected damp proofing, typical job | £1,000–£3,000 | Checkatrade |
| Chemical damp proof course, installed | £650–£3,400 | MyJobQuote |
| Physical damp proof course fitted to an existing wall | £2,500–£7,500 | Checkatrade |
| Damp proof membrane on walls, per m² | £80–£140 | MyJobQuote |
| Cellar or basement tanking, per m² | £100–£200 | Checkatrade |
Sources: Checkatrade damp proofing cost guide (last updated June 2026), whose figures are plus VAT and leave out removing and replacing plaster, decorating and surveys; and MyJobQuote damp proof course costs (updated 7 September 2026), which covers materials, labour and clearing up but not the survey, replastering or decoration. The two guides measure slightly different things, which is why their ranges differ.
What moves the price: how many metres of wall need treating, whether walls are solid or cavity, how much plaster has to come off and go back, access, and whether the outside needs work first. Replastering can cost as much as the injection itself.
Facts, dates and prices on this page were last checked on 29 October 2026.
The full breakdown, with what pushes prices up and down, is in our damp proofing cost guide.
Common questions
Does every damp wall need a new damp proof course?
No. A damp proof course only deals with water rising from the ground. If the damp is condensation, a leak or rain getting in, a new damp course won't help. Ask the specialist to explain how they've ruled the other causes out.
How long does damp proofing take?
Injecting a damp proof course into one or two walls is often a day's work. Replastering adds time, and the wall then needs weeks or months to dry out before it's decorated with anything but breathable paint. The specialist should tell you how long to leave it.
Do I need to move out?
Usually not. Expect dust, furniture moved away from the walls, and skirting boards taken off. Tanking a cellar or replastering several rooms is more disruptive, so ask what to expect.
What should the guarantee cover?
Ask what it covers, for how long, whether it transfers if you sell, and who stands behind it if the firm closes. Some guarantees are backed by an insurance policy, which is worth more than a firm's own promise.
My mortgage lender's survey says I need damp proofing. Should I just do it?
Get the cause checked first. Valuation surveys often flag high meter readings without finding where the water comes from. An independent damp survey can save you paying for a treatment you don't need.
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