A damp proof course, also known as a damp proof membrane, is a form of moisture control for your home. Commonly made of bitumen, plastic, slate or tin, they stop moisture from travelling into porous masonry. They're usually installed beneath floor level under a suspended timber floor or right above your floor slab if you have a solid concrete floor. A good damp proof course should last between 10 and 20 years but sometimes they stop working.

If your walls are showing:

Mould growth

Yellow or brown tide-like stains

Blistering, peeling or powdery paint

Salt deposits

Peeling wallpaper

Decaying skirting boards

— there's a high likelihood your damp proof course has failed.

And if you feel sick when you're inside your home, that's a definite sign the interior is too damp because your course isn't working.

Read on to learn some of the most common causes of damp proof failure.

One of the most common reasons for deterioration of the membrane is age. Bitumen, plastic, slate or tin membranes don't last forever. As they're blocking moisture all of the time, they naturally get worn down over decades.The other thing that can accelerate the deterioration of a damp proof course is the presence of too much moisture in the ground. Soil can be oversaturated because of leaking underground pipes. Water may also be travelling towards your home because it's at the bottom of a hill.

In a nutshell, bridging occurs when water gets above your damp proof course. This can be because the ground level outside your home's external walls are above where your damp proof course was installed. It can also be because cracked gutters are running rain water down your home's exterior walls off your roof. Bridging can also occur when heavy rain bounces off the ground and splashes up against the wall above the course. And if you have heavy climbing plants such as Ivy running up your external walls, they'll be carrying moisture as well, which can also cause bridging. Whenever water is getting above the damp proof course, external walls soak up moisture which eventually leads to failure of the course.

When installing a new membrane, wet brick needs to dry off and contaminated plasters need to be completely replaced. Ample time needs to be allowed for walls to dry off before installation of a brand new course.A rushed installation means the liquids in your walls don't have time to evaporate. In turn, the salts inside your walls will still be there and attract even more moisture in the future. By rushing installation, you're rushing the failure of your damp proof course.

If you're seeing the tell-tale signs of rising damp, it's likely your damp proof course has failed. DampBlock™ AQ50 creates a permanent new DPC inside the wall — stopping moisture in its tracks even if it's bridging your old course. A free assessment measures the moisture levels and explains exactly what damp proofing can do.