Hello all.

We have bought an old granite house to completely renovate high on the Plateau Millevaches in Limousin, Central France. The house is built into the wooded hillside so at the front there are two storeys but at the rear the second floor is at ground level. There is a flat terraced area behind the house which is just well drained earth/grass.

There are a couple of major issues we need to address. As I mentioned the house is of granite construction with solid walls of about 600mm thick. The whole of the kitchen/lounge and adjoining stable has the rear wall below ground level. For years there has been no guttering on the roof so especially at the rear rainwater has been concentrated. The walls on the exterior have also been partially rendered with hard cement as a splash back and then with horrible cement ribbon pointing or just smeared cement pointing. We obviously need to remove ALL of this and repoint with breathable lime and sand mix to let the walls BREATHE!!

What we need suggestions and advice on is a.) what tools can we use to remove the cement render and pointing. (It is stubbornly hard) and secondly what can we do to solve the damp in the rear wall of the house?

We are planning a new roof with zinc guttering and full drainage away from the house. Should we excavate behind the house and install a honeycombed membrane against the rear wall right down to floor level on the first floor and then refill with gravel?

On the inside at present in the kitchen lounge area has a secondary stone wall (on ground floor level only) which has been added at some point as the beams had rotted out in the original wall sockets!! Not sure why they didn’t replace the beams instead? This wall is about 500mm thick!! We plan to remove it as all new beams will be going in and fixed to a wall plate which will be fixed to the original wall. This secondary wall has signs of damp in it and crystallisation ( effervescence). There is about a 50mm gap between these walls.

In the adjoining stable the rear wall is original but it feels damp to the touch and the joints ( possibly old lime) are quite wet and crumbly?

We need to insulate and stop the damp coming in? We could build a new secondary wall with an air gap but were hoping to use hemp lime or a hemp block wall? Obviously we need to limit damp penetration which is tricky as the wall is below ground? Is external excavation our only option?

Interested to hear suggestions? I feel we have taken on a huge project!!

Posted By: LehobbitI feel we have taken on a huge project!!

Yup !

Has the house been recently lived in / heated? if it has been empty for a while then this will add considerably to the damp.

Re making the walls breathable - if the place is built of granite then the stone is fairly (very) impervious so the only place any breathing will happen is at the mortar joints and as a %age of the wall area - not much.

I have a house that has a basalt stone / rubble /earth ground floor construction (200 years old) which has the rear built into a hill of sandy soil. I lined the wall with a VCL (aka plastic sheet) and built a single skin wall in front of it. In 25 years there have been no problems and no damp.

Posted By: LehobbitWe need to insulate and stop the damp coming in? We could build a new secondary wall with an air gap but were hoping to use hemp lime or a hemp block wall?

If it were mine I would put a VCL against the original wall, then EPS insulation then standard internal wall building blocks then plaster. Although reading above where you plan to replace the beams to a wall plate I would make the new false wall load bearing (20cm porotherm or equivalent) and sit the beams in that.

Posted By: LehobbitIn the adjoining stable the rear wall is original but it feels damp to the touch and the joints ( possibly old lime) are quite wet and crumbly?

Cold and damp can feel the same - and if it is cold i.e. ground temp (12 deg.) because it is unheated and below ground level then it is probably below dew point so condensation will be there and in such a situation the lime mortar will be wet so IMO it could be difficult to differentiate between the above and penetrating damp from the ground (could have both of course)

For the outside at the rear I would put up guttering as a first job and then put in a french drain (with a good out flow) to a depth of 750mm and see what happens. Although if an new internal wall with a VCL is built then it may be difficult to see which of the remedies had the best effect.

I would leave the cement render and pointing for a later time although where there is render this would be a good candidate for EPS external wall insulation (EWI) straight on to the render I have done this to my 2 basalt stone houses with very good results. (One, a rented house, had continual black mould on a little used room north wall. 10cm EWI produced an instant fix - a warmer room and no mould ever again). If the pointed stone is not needed for aesthetic / visual value then I would EWI this as well (again straight on to the stone wall).

Good luck Lehobbit!

Have you considered using the earth bank to store solar heat, like in an 'Earthship’? The idea is you fit a lot of glazing to let solar heat into the house . The stone wall and earth bank soak up the heat, thus preventing overheating in summer. Eventually the exposed face of the wall warms up above dewpoint temperature and then dries out by evaporation. The heat is retained in the earth by the insulating effect of many metres of earth.

For this to work you have to stop water soaking down through the bank from the top surface, and ideally stop heat escaping to the surface. One way to do that would be to build a lean-to extension at the upper floor on top of the bank.

You should certainly seek specialist advice, not a general architect, as it sounds like the earth bank is helping to prop up the wall, don't dig big trenches into it or dry it out until you understand the possible effect on the building.