DPC Injection and Damp Proof Course

A damp proof course, or DPC, is the barrier near the base of a wall that stops ground moisture rising into your home. When an old slate or bitumen course fails, or a house was built without one, we install a new chemical DPC using a BBA approved system.

When do you need a new damp proof course?

Houses built before about 1875 often have no damp course at all. Victorian and Edwardian homes usually have slate courses, which crack as buildings settle. Interwar homes often have bitumen felt courses that become brittle with age.

Even a working DPC can be bypassed. Raised patios, flowerbeds, driveways, render taken down to ground level and internal floors laid higher than the course can all bridge it.

How DPC injection works

Our injected damp proof course is installed in the mortar line just above external ground level.

Drilling

Holes are drilled at set intervals into the mortar course along the affected walls, inside or outside as the job requires.

Injection

A BBA approved damp proofing cream is injected. It spreads through the mortar and cures to form a continuous water-repellent layer.

Making good

Holes are filled, and internal walls are replastered with a salt-resistant system where plaster has been damaged.

How chemical DPC cream injection works

Chemical DPC cream is a thick, silane-based cream rather than a liquid, so it stays where it is put. It is pumped into a continuous line of holes drilled into a horizontal mortar joint, usually the lowest one that sits above outside ground level and below the internal floor.

Over the following weeks the cream diffuses into the surrounding mortar and brick and cures, lining the pores with a water-repellent layer. Ground water can no longer climb past that line, and the wall above starts to dry out slowly. Because the cream is placed in the mortar course rather than through bricks, the finished work is barely visible from outside once the holes are filled.

The cream is only one part of the job. Salt-damaged plaster has to come off and be replaced with a salt-resistant system, or salts left in the wall will keep pulling moisture from the air. Read more in our guides to salt on walls, replastering after damp proofing and what drives the cost of a DPC.

Checking the outside first

Before any injection we check outside ground levels. External ground should sit at least 150mm below the damp course. If it does not, we will tell you what needs lowering, because no DPC can work if soil or paving is piled above it.

We also look at air bricks, rendered plinths and gutters, so the new course is part of a complete solution rather than a quick fix. Our guide to checking for DPC bridging explains what to look for.

Guaranteed, trained and trusted

All our DPC work comes with a 20-year guarantee certificate on completion. Our technicians are PCA trained and Safeguard Ltd trained, and Seth Long and the team bring over 30 years' experience to every job.

We are rated 9.82 on Checkatrade from 389 reviews and 4.9 on Google.

Damp proof course (DPC) installation questions

Is DPC injection messy?

Some dust is unavoidable when old plaster is removed, but we protect floors and furniture and clear up at the end of each day.

Can a DPC be installed from outside?

Often yes, depending on wall construction and access. We will recommend the best method after the survey.

Do I need to move out?

No. Most homeowners stay in the property while the work is carried out.

What is DPC cream?

It is a silane-based damp proofing cream injected into the mortar course. It cures inside the wall to form a water-repellent barrier that stops ground moisture rising.

DPC injection and damp proof course installation