Did you mean breàthable Rôbert?
Erm, in a word, No. I mean waterproof, which I know will be contested as to advisability by some folks.
I’m not prepared to live in a damp house, so when I came here over 20 yrs ago I set about preventing the ingress of damp through the walls and banishing the spores of mold and fungus, as well as the insects, from the interior living space.
I was told at the time by a professional plasterer that it wouldn’t work. He was wrong. Problem walls have been sealed with polystyrene panels (2 layers with offset joints), and after all this time the plasterboard hasn’t come away from the wall, and the wall hasn’t fallen down. Interior generated dampness is dealt by extractor fans vented to the outside. What I have now is a dry interior to my home that needs no dehumidifiers and which costs less to heat in winter.
Seems to me that the proof of the pudding is in the eating.
Maybe hemp lime plaster on interior walls - insulation that breathes…
My thoughts on insulation having been somewhat schooled on breathable insulation for solid walled buildings makes me wonder if the non breathable insulation was thick enough there would be little warm to cold surfaces to cause mould behind any panneling. I have removed thinner non breathable insulation to find the wall black with mould due to no air movement and a warm surface to cold surface condesation issue. At least with breathable and a vapour membrane you are resonably safe from mould issues.
I agree that there can be ‘dew point’ condensation issues within a wall which will encourage mold growth, especially where the room is overly humid due to inadequate ventilation. No doubt the point of the one way vapour membrane (if fitted immediately behind the plasterboard finish), is to stop the humid air within the room from penetrating into the wall. This does however create a two stage process with costs related to both materials and labour.
If one uses a waterproof interior insulation such as plasterboard with a layer of polystyrene bonded onto the back, gluing it to the wall is just a one step job.
The polystyrene is waterproof in both directions and so humid air from inside the room cannot enter the wall beyond the back of the 10mm thick plasterboard layer. The temperature loss during that 10mm of travel is insufficient for there to be any danger of condensation within the wall from the penetration of interior humidity which cannot pass through the waterproof insulating layer.
In this particular thread we are told by @Jim24 that the house “is damper than a modern construction”, and no doubt this may well cause problems and damage to items stored within the premises.
Using a breathable insulation is going to allow the damp that it is inside the walls to escape into the building, which I would venture to suggest simply augments the problem of interior humidity rather than causing a reduction.
In my view it is always better to address the root cause of a problem rather than to just treat the symptoms, although I do realise that this can sometimes be difficult to achieve, and at times impossible.
In my experience, damp walls are caused by leaking roofs and gutter systems, insufficient resistance of the exterior surface to wind driven rain, or good old rising damp, the latter being the most problematic.
Jim has mentioned the absence of a damp proof course which may indicate a rising damp problem in relation to which there are a number of helpful alternatives to be considered.
Firstly, one can improve outside land drainage reasonably adjacent to the wall, especially if the surrounding land has a slope down towards the wall.
Secondly, one can plant some bushes or climbing roses against the wall which, once established, will draw large quantities of water out of the ground on a daily basis. (My roses look beautiful as well as drying the ground.)
Thirdly, if there is a void space under the interior floor (the so called ‘vide sanitaire’), then providing some below floor level air vents through the walls will help to dry things out.
Old buildings are always a challenge and are something of a ‘labour of love’.
However, I do think that just because a wall has been damp for 100 yrs or so, doesn’t mean that preventing that damp from entering the living space is going to cause it to fall down. If back then the relevant waterproof insulation had been available I’m sure that the original builders would have used it. I mean, who would choose to build a damp house ?
Maybe the building was once a grange or moulin, not originally designed to be lived
The new roof and gutters have made a dramatic difference to the internal humidity levels, as has ongoing external landscaping, so it’s all heading in the right direction.
Many of the small planks beneath the old hand-made roof tiles were thin hand hewn oak, but generally too far gone to meaningfully salvage. Many of the tiles have been rescued, each one of a unique size and colour. I’m told that in the day the wet clay slabs were folded over women’s thighs to produce the final shape, and when handling them that thought makes me wince - surely it’s a rural myth?
I make my own breathable internal wall plaster using crushed limestone sand and lime, with long thin flakes of pine acting as a binder, and have been experimenting using mortar dye in the mix to give it some earthy colours, but it’s early days. It’s not just a question of the colour of the dyes, but also the concentration, and the changes that occurs when it dries out. Interesting.
The Hovel was definitely used as a house, with hay stored upstairs which will have provided some limited insulation in bygone times. There are vertical slots built into the external walls that provide some direct ventilation, which I am progressively sealing up with small windows and a separate steel framed stainless mesh to try and stop the doormice from entering at will every Autumn.
It was last used by the old Maire as a base for his Hunting Crew - it was full of woodworm infested old wooden benches and trestle tables, plus lots of those heavier old-fashioned wine bottles.
The last family lived there until the 1950’s, with 7 children, all in three rooms with just an open fire and no running water or electricity (they came in the late 1960’s). No toilet either of course, and which part of the garden contained the Earth Closet remains a mystery. I bet they couldn’t wait to get to a town or city - particularly the kids?
Lime is the binder, where did adding pine come from? Chanvre is sometimes used for an insulation addition.
That is very good news. Just remember that those walls have been damp for a very long time and so it is going to take a long time for them to dry out. Probably at least two years is not an unreasonable time frame, and the thicker the wall, then the longer it will take.
I have a couple of carpenter friends with workshops, and a neighbour bought his in from a specialist builders merchant in large sacks which gave me the original idea.
Ok Jim I was interested as having done a fair bit of restoration of old buildings I hadnt come across it before.
As you havent used any cement in the mix you can also lime wash with some great colour tinting to add interest. Unfortunately on mine the two french masons who worked for me sneaked in bags of white cement into the chaux so I sacked them both. Now I cant lime wash.
Adding a touch of cement to the mix is quite common locally as I understand that it accelerates the setting time, but I didn’t appreciate that it meant that you couldn’t lime wash afterwards. Presumably that’s because cement is rather more water resistant, and may explain why limewashing hasn’t worked on some of my inherited plastered walls.
I’m gradually working my way round all my walls, both internal and external, removing all traces of cement mortar that I find. That they also look so much better afterwards is just a bonus.
The use of cement mortars on these old buildings is simple vandalism - prevents the walls from breathing, trapping moisture, and can cause external stone faces to burst when there is a frost. It should only be used with bricks and concrete blocks, and even then I add some lime to improve the workability and to reduce the likelihood of expansion cracking. I find most cement mortars mixes used are far too strong for their intended application, my blockwork standard being 4 parts sand, 1/2 part lime, 1/2 part cement.
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Yes a nephew trained by a local artisan mason trained him to add cement to lime mortar. That lead to a very heated discussion. The nephew no longer adds cement and left that employer shortly after. Just to make something have an initial set so they can finish a bit earlier is not reason enough to screw up a natural stone wall in my book or in historic Englands who I have worked with.
The people who built Stonehenge didn’t use cement. Just saying. 
My lime mortar sets just fine without needing any cement adding, but
then again I don’t build external walls during the Winter or when it is
raining. My experience is quite the opposite - I use lots of water to
dampen everything down both before, during and shortly after
construction. I use lots of sacking and plastic sheets to hinder
drying-out.
The great Wall of China was built using lime mortar plus a few other
choice additives:
Another bonus is that lime requires significantly less energy in it’s
production than the much hungrier cement, plus lime mortar constructions
weather more gracefully into their surroundings.
Over the last thirty years many of my local French Towns and Villages
such as Verteillac have "“smartened-up” their civic centres, and it’s
all done with cement and concrete. It’s vandalism, and I’m grateful
that I experienced it before the gentrification.
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