The DIY Fix is reader supported. When you buy after clicking a link on our site, we may earn an affiliate commission.
Damp can often be a word that strikes fear into homeowners and also potential homebuyers. When damp is found in a house survey, it is one of the most common stumbling blocks in the house-buying process. So what do you do if you find damp in a property? Well, one solution is an injected damp proof course. Here is everything you need to know about what an injectable damp course is, and how it is used to solve damp problems in the home.
Damp – The Basics
To properly understand what an injected DPC (Damp Proof Course) is and how it works, first you need to understand what rising damp is and the problems it can cause.
In a property with no damp proof course (or where the DPC is damaged) – due to capillary action or ‘wicking’ (when liquid flows in narrow spaces unaided) – water can rise up through a wall. This will often go unnoticed at first but over time it will become visible and make plaster pop and begin to crumble. Damp spots can emerge on internal walls and if left untreated mould will begin to form. It is sometimes confused with condensation damp – which is common, particularly in poorly ventilated and heated spaces, but rising damp will only continue to get worse – and this is where an injected damp proof course comes in.
Why is an injected damp proof course the solution?
Damp will occur if there is no damp proof course in a property. Most houses built in the last 100 years will have had some sort of DPC fitted. Traditionally, this was in the form of a layer of slate. Plastic membranes are the most widely available method nowadays. You can usually see the existing DPC in your property by looking at the external wall. Where you can see a thin black line about six inches up from the ground, that’s your DPC.
But slate can crack, and no damp proof course lasts forever – and one of the best remedial actions to take is an injected damp course.
What is an injected DPC, and how does it work?
The clue is in the name really; an injected DPC literally injects chemicals into the external wall of a property to form an integral layer of protection that water cannot penetrate.
As bricks are porous, they will soak up the chemical waterproofing liquid. When the liquid sets the protective layer is established. This essentially means that any moisture below the DPC will not be able rise above it.
The alternative – fitting a new damp proof membrane (DPM) – is obviously very difficult and costly to do as the wall is already built. This is why chemical damp proof injection has become the most common method of damp proofing this situation.
Usually the chemical damp proof course is injected into 12mm holes that are drilled at 100mm intervals along the line of the course. High-pressure or drip-feed systems can be used, and creams can also be used to squeeze into the drilled holes.
Does the internal wall need to be treated?
This is a ‘Damp FAQ’ – and the answer to it is, yes. Plaster on the internal wall will need to be removed to release any trapped moisture. Typically, plaster is removed to 1.2m up the wall. Due to the effects of wicking, it’s often a good idea to go a little higher – to 1.5m. If in doubt, seek advice from a CSRT (Certified Surveyor in Remedial Treatments) who will be able to tell you how far water has travelled up the wall and to what level plaster will need removing to.
DIY Injected Damp Course
It is possible to carry out an injected damp proof course yourself. DIY kits are widely available. It is vital that you use BS standard injection product though. Also, if you want to do it yourself, it’s definitely worth investing in a decent kit – don’t go for the cheapest option!
You should never try to cut corners with an injectable damp proof course. Having it properly installed by a professional will give you an insurance-backed guarantee of 30 years or more.