Damp Proof Course Installation in North London
A failed DPC lets ground moisture climb your walls. We arrange chemical DPC injection to BS 6576 — and honest surveys that tell you when a cheaper fix will do.
What is a damp proof course? A damp proof course (DPC) is a horizontal water-resistant barrier built into walls near ground level to stop moisture rising through masonry by capillary action. Victorian and Edwardian houses used slate or bitumen courses; modern buildings use plastic membrane. When an original DPC fails or is bridged — the usual situation in North London's period stock — a replacement chemical DPC is installed by injecting silicone cream into the mortar bed to BS 6576, followed by salt-retardant replastering. Installed correctly it lasts 20–30+ years.
Understanding the problem
Three DPC situations account for almost every case we see in North London. First, decay: slate courses crack as buildings settle and bitumen embrittles, opening capillary paths after a century of service. Second, bridging: the DPC is intact but something carries moisture around it — raised paths and flowerbeds, render lapped below the course, internal plaster crossing it, or rubble in a cavity. Third, absence: many pre-1875 buildings were simply built without one.
Only the first and third genuinely need a new DPC. Bridging needs the bridge removed — lowering ground levels, cutting a render bell-mouth, clearing debris — which is cheaper and more effective than injecting through a bridged wall. A survey that doesn't check external levels before recommending injection is not a survey worth paying for.
Signs and symptoms
- Confirmed rising damp: tide marks, salts and blown plaster at low level
- Visible decayed or missing slate/bitumen course at the external wall base
- External ground, paving or render level with or above the DPC line
- Damp returning after previous 'treatment' that skipped replastering
Common causes
- Age-related failure of slate or bitumen courses (typically 100+ years old)
- No DPC in pre-1875 construction
- Bridging by raised ground levels, render, plaster or cavity debris
- Poorly installed previous chemical DPC (wrong course, wrong spacing, no replastering)
Getting the diagnosis right
Before any injection, a competent surveyor confirms genuine rising damp with moisture profiling and salts analysis to BS 6576, locates the existing course, and checks every potential bridge. The written report should state which mortar bed will be injected, the drilling pattern, and the replastering specification — the plaster system does half the work, because it holds back residual hygroscopic salts while the wall dries. Full detail in our DPC guide.
Treatment
- Preparation — skirtings removed, contaminated plaster hacked off to ~300mm above the highest damp reading.
- Injection — holes drilled at ~100–120mm centres into the selected mortar course; silicone DPC cream injected to full wall depth, lining the capillaries with a water repellent that cures into a continuous barrier.
- Replastering — salt-retardant renovating plaster or membrane-backed board system, carried down to the new DPC level, never bridging it.
- Drying & decoration — walls dry over 6–12 months; breathable emulsion until fully dry, then normal decoration.
What does it cost in North London?
| Item | Indicative range |
|---|---|
| Damp survey | £280 – £450 |
| Chemical DPC + replastering | £70 – £120 per metre |
| Single wall (4–5m) | £800 – £1,500 |
| Whole ground floor, mid-terrace | £2,500 – £5,000 |
| Bridging remediation only (ground lowering etc.) | £200 – £900 |
Beware per-metre prices that exclude replastering — that is where failed DPC jobs usually cut corners. Figures are indicative for North London (2026) and vary with property, access and scope — written quotations follow a survey. See the North London Damp Cost Guide or try the Damp Proofing Cost Calculator.
Our process
Tell us the problem
Call or use the contact form — describe what you're seeing and where. Photos help.
Survey & diagnosis
An independent qualified surveyor inspects the property and identifies the true cause, with a written report.
Clear written quote
You receive a costed scope for exactly what the property needs — no more, no less.
Treatment & verification
Works are carried out by vetted independent specialists, with guarantees where applicable and verification that the fix worked.
Frequently asked questions
Indicatively £70–£120 per metre including salt-retardant replastering — about £800–£1,500 for a typical wall and £2,500–£5,000 for a whole terraced ground floor. If the existing DPC is merely bridged, remediation can cost as little as £200–£900.
A silicone-based cream is injected into holes drilled along a mortar course. It diffuses through the mortar, lines the capillaries with a water-repellent silicone resin and cures into a continuous barrier that stops moisture rising — the modern method recognised by BS 6576 and PCA guidance.
Original slate courses often lasted over a century. Modern chemical DPCs are typically warrantied 20–30 years and frequently outlast that, provided the correct course was injected and replastering was done properly.
Almost always, where rising damp was established. Ground moisture leaves hygroscopic salts in the plaster that keep absorbing airborne moisture even after the wall below is dry — so old plaster stays damp-looking forever. Replacement with a salt-retardant system is part of the fix, not an optional extra.
DIY cream kits exist, but the failure points are diagnosis and replastering, not the injection itself. Injecting the wrong wall (condensation misdiagnosed as rising damp), the wrong course, or skipping salt-retardant replastering are the classic DIY failures. For anything beyond a single garden wall, professional installation with a warranty is the economical choice.
Worried about damp, mould or a wet basement?
Speak to us today or book a survey — we'll arrange the right independent specialist for your property.