What Is a Damp Proof Course (DPC)? A Plain-English Guide

The damp proof course — or DPC — is the horizontal waterproof barrier built into every wall about 150 mm above ground level. Its only job is to stop ground moisture wicking up through the porous brickwork by capillary action. When it works, you never think about it. When it fails, you get rising damp.

What a DPC is made of

• Pre-1980 homes: bitumen felt or a thin lead sheet. Lifespan: 30–50 years.
• 1980s–2000s: black polyethylene (plastic) sheet. Lifespan: 40–60 years.
• Modern builds (2005+): DPC membrane plus a chemical DPC injection at slab level.

How to tell if your DPC has failed

• Classic tide-mark up to 1 m off the floor.
• Salt bloom (white crystals) along the skirting.
• Skirting boards rotting even though nothing is leaking above.
• Home is older than 30 years and has never been re-treated.

The old way to replace a DPC

Cut a slot right through the wall, insert a new plastic membrane, and re-mortar. Effective but disruptive, expensive, and structurally risky. Nobody does this anymore for residential work.

The modern way — chemical DPC

A micro water-repellent liquid is applied to the wall (or injected into holes drilled at DPC height on thick walls). It penetrates the brick and creates a new hydrophobic barrier without breaking the wall open. This is what Damp Gone Xtreme does — the same chemistry contractors use, in a bottle you can apply yourself.

DIY or professional?

Single-storey internal walls: DIY in a weekend. External walls, double-storey, or heavy salt damage: book our professional damp proofing service — chemical DPC with a 10-year written guarantee.