Damp-Proof Course (DPC) Injection: What It Involves and What It Costs
4 August 2026 · 1 min read
A damp-proof course is a physical or chemical barrier built into a wall, just above ground level, to stop groundwater wicking upward into the brickwork. Older properties (particularly pre-1875 or so) sometimes have no DPC at all; in others, the original DPC has failed, been bridged by a raised flower bed or path built up against the wall, or damaged during renovation work.
What the treatment involves
Chemical DPC injection involves drilling a series of holes along a mortar course near the base of the affected wall and injecting a water-repellent chemical (usually a silicone- or siloxane-based cream or fluid) that spreads through the masonry and creates a barrier to rising moisture. It’s typically followed by re-plastering the lower section of the wall with a specialist salt-resistant render, since the original plaster will usually be contaminated with salts drawn up by the damp and won’t simply dry out and become sound again.
Before you agree to it
- Confirm it’s actually rising damp first — see our guide to telling damp types apart. Genuine rising damp is much rarer than the number of DPC injections sold each year would suggest.
- Get an independent survey where possible — ideally from a surveyor who doesn’t also profit from carrying out the treatment, since that removes the incentive to over-diagnose.
- Check for bridging first — sometimes the fix is as simple (and far cheaper) as lowering an external path or flower bed that’s been built up above the existing DPC, rather than an entirely new chemical injection.
- Ask about the guarantee and whether it’s insurance-backed, since damp-proofing companies do go out of business.
Cost
Cost depends heavily on the length of wall being treated, whether replastering is included, and regional labour rates. Because prices vary so much and the market includes some aggressive up-selling, get at least three quotes and ask each one to explain exactly what evidence they’re basing the “rising damp” diagnosis on, rather than accepting a verbal assessment alone.