Fed up with the amount of dust coming off the floor, so sealed with PVA(Get it from Color’i a chain of art shops, cheaper than Brico Depot) , and painted with Castorama floor paint, 14 Euros a tin, coverage not quite as much as it says on the tin!
Red Concrete Floor
Corrugated steel sheet concrete shoot supported by scaffold tube
During the wait for the concrete to arrive, a few worse case scenarios are discussed, the worst of these being that the concrete conveyor would not reach the back of the barn and we would have to move it from half way inside to the rear wall, so a shoot was constructed from some corrugated steel sheet.
When the concrete for the barn floor did arrive, it arrived on a truck without the conveyor that had been ordered, a scenario far worse than our previously envisaged worse case scenario!
Concrete shoot with buckets to catch the mix that was pouring out of the gaps
The corrugated sheet was clamped to the mixer shoot, and some storm guttering supported at the bottom of the steel sheet. Using this method we managed to move the concrete about 4m to the back section of the barn.
I didn’t intend to put any concrete in the front of the barn, but we put a damp proof membrane and some shuttering in, so that we could dump any excess concrete there.
French DPM at the front of barn
The back of the barn is the largest area to concrete.
Damp Proof Membrane
The wet concrete floor 15 minutes after pouring.
Barn floor tamped and wet
Concrete floor doorway shuttering
The doorway is shuttered off,so that I can make a step up into the back of the barn at a later date.
3 hours 40 minutes after the 6.5 cubic metres of concrete arrive, the truck is cleaned and ready to leave
Concrete mixer truck cleaning
The floor can be walked on 24 hours after it has been poured, the shuttering is broken off, and any concrete that is in places is shouldn’t be is chiseled off.
concrete floor dry and ready to seal
It’s a lot easier to get the water in and sewage out of the barn under the doorway than digging under wall. I have also added a red plastic cable protector so that the electric could enter below the door if necessary.
Mains services in concrete floor slab.
The steel grid is not really required because the floor is not load bearing, but the cost is minimal compared to the cost of the concrete, so we might as well chuck some in!
The back of the barn is divided into 3 bays each bay about 2.5 metres wide, meaning that it can be tamped with a 3 metre aluminium tamping thingy.
Originally I was going for 100mm of concrete, but 80mm seems the norm in France. When in France ….
Shuttering for the barn floor concrete slab
6 cubic metres of concrete will cover the entire barn floor at 80mm coverage.
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”.
The barn has a cobbled floor in the front section and compacted soil floor at the back. A damp proof membrane can either go above or below the concrete floor. I have decided to put a damp proof course under the concrete, but I may an additional one on top of it when its finished and then screed over it.
A concrete pump to pump the mix to back of the barn costs an additional 150 euros.
It seems common practice to put steel in concrete floors, but Roy and Roger say it’s not necessary as the floor is not structural. If I can get the C25 mix for less than 950 euros that Point.P have quoted for 6 cubic metres and 10 metre concrete pump then I might put some steel in just in case the floor becomes load bearing in the future.
6 Cubic metres of C25 concrete should be enough for 100mm thickness of concrete over the entire floor area. At some point in the future the floor should be covered with insulation and then another 100mm of concrete.
Concrete reenforcing bar (rebar) for french barn floor slab
When I return to France I will visit Leclerc and Reseau Pro to see if they can beet the Point.P quote for C25 Mix, Leroy Merlin in Poitiers also supply readymix concrete but I imagine the distance that they are from the barn will make them the most expensive concrete supplier.