Properly diagnosed and installed damp proofing should last for many years, but how long depends on the system, the installation and whether the original cause, such as bridging or leaks, was dealt with. Ask for a written guarantee, and ideally an insurance-backed guarantee that protects you if the company stops trading.
People want to know whether they’ll have to do it again in ten years. If it’s the right treatment, installed properly, for the right problem, there’s no reason why damp proofing shouldn’t last a very long time. The failures I see are almost always down to one of three things.
Why damp proofing fails
- Misdiagnosis. The wall had penetrating damp, condensation, a leak or a bridged DPC, and a new DPC was injected instead. The original cause carries on.
- Poor installation. Injection holes in the wrong place or too far apart, not enough product, or walls not fully treated.
- Replastering done wrong, or not at all. Salt-contaminated plaster left on the wall, gypsum plaster used straight onto salty masonry, or plaster carried down onto the floor so it bridges the new DPC.
Things can also change afterwards. Someone builds a patio too high, a gutter starts leaking or the render cracks, and damp comes back for a new reason.
Guarantees
- Ask for the guarantee period in writing before you agree to the work, and what exactly it covers: the DPC, the replastering, or both.
- Ask whether it’s insurance-backed. A company guarantee is only worth something while the company is trading. An insurance-backed guarantee can protect you if the contractor goes out of business. Ours are provided through QANW (Quality Assured National Warranties) and cover our damp proofing, timber treatment and waterproofing work, on top of our own free standard guarantee.
- Check for conditions. Some guarantees are only valid if you do certain things, like keeping ground levels down or maintaining gutters. That’s fair if it’s explained. Be wary of conditions designed to avoid responsibility, such as a guarantee that only applies if you also buy a ventilation unit you didn’t need.
- Keep the paperwork. If you sell, a buyer’s solicitor will usually ask for the guarantee, so make sure it’s transferable.
Choosing a contractor
Look for a PCA member company with qualified surveyors, a clear written report explaining the cause, an itemised quote, and a guarantee you understand. Cheapest isn’t always safest. A job that has to be done twice is the most expensive job of all.
When to call a specialist
If you're weighing up damp proofing quotes or have damp coming back after treatment, get a qualified survey and ask exactly what the guarantee covers. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
Listen on The Damp Show
Frequently asked questions
What is an insurance-backed guarantee?
A guarantee backed by an insurer that can protect you if the contractor stops trading.
Why has my damp proofing failed?
Usually misdiagnosis, poor installation or incorrect replastering, or a new cause such as bridging.
Are damp proofing guarantees transferable?
Many are, but check the terms, as buyers' solicitors often ask for them.