Damp proof courses are a routine requirement for many old houses when you buy them. Surveyors reports will nearly always find some damp and hence will stipulate the need for a damp proof course to be installed. But is it possible?
The old walls of many of the terraces in SE Wales (and beyond) are made up of face stone and a rubble fill. This means that they are very thick and also in the main made of lumps of stone, broken brick and some lime mortar. There are voids everywhere and the stone can be a right old mix of different sizes, shapes and types. So trying to damp proof these with a pressure spray or cream is doomed to failure. Spray will just find all the cracks and voids and the cream will be pumped into a mix of voids, stone, brick and mortar. So these techniques really will have minimal effect. So are there any others?
I have written before on the blog regarding the use of breathable renders and paints and these can certainly be used to dry out a building if specified and used correctly. Maintaining air gaps and air flow under suspended floors also helps significantly, however for many people they are faced with owning a house that has been cement rendered and concrete floors installed, so is there an alternative?
Personally I think that there are two.
Where you have old brick solid walls, these can be treated by using the creams (injecting the cream into the lime mortar rather than the brick) and ensuring that the holes are filled in afterwards (otherwise rainwater gets into the holes and then cannot drain down and hence causes more damp!).
Where you have the solid rubble filled walls we have to be a bit more clever. There is a system called Electro-Osmosis where you introduce a small electric charge to the wall using titanium rods and these create a positive charge in the wall. Water carries a positive charge as well, so the wall repels the rising damp. See diagram below.
These trickle charge systems are really effective and are not as expensive as might be imagined. However as with all damp, any plaster / render effected might have to be replaced as they are probably affected by salts.