How to install a damp proof course in a stone barn with concrete slab floor …
If you are going to join 2 sheets of damp proof membrane or join to a damp proof course in the walls then you must overlap by 150mm.
DPM Jointing/Repair Tape
The damp proof membrane should be joined with double-sided mastic strip, or butyl tape to create a waterproof barrier, and then seal down the edges with jointing tape.
The damp proof membrane should normally be covered with a layer of soft sand to act as a protection and to prevent damage when the concrete flooring or screed are installed.
Damp proof membranes can be installed over or under the concrete slab, the advantage of installing under is that the dpm will prevent any moisture reaching any re-enforcing steel in the slab and it will also retain liquid in the concrete, slowing down the hardening process and ultimately giving a stronger concrete slab floor.
Polystyrene foam, Kingspan or Celotex can go either above or below the concrete slab, 10% of heat in a building is lost through as uninsulated floor.
Installing a damp proof course in an old stone wall and fastening it to a DPM is another problems, on greenbuildingforum.com somebody suggests removing a stone at a time and unrolling the DPC in the gap, then replacing the stone and removing the next one. This won’t work on my barn because the walls are made of rubble and they are probably to thick for a traditonal DPC anyway.
Silicon injected damp proof course do not work on rubble stone walls either, so the other suggestion of Green Building Forums was “Electro-osmotic damp-proofing”. A company called Lectros manufactures an Electro Osmotic Damp Proofing system, on their website they claim that, “The system introduces a very small and perfectly safe electric current into the wall just above ground level through a series of titanium anodes inserted into the brickwork. Its effect is to repel the rising moisture molecules down the walls and harmlessly back into the ground. As long as this tiny positive charge is maintained, the protected walls remain dry and totally free of damp.” . The Lectros system works for some people and not others.
The one solution that comes up time and time again for avoiding damp in rubble stone walls is “use lime inside and out = no more damp problems”.
