I have a thick stone wall and I want to insulate it from the inside.

Currently the wall is covered by some old wallpaper and some parts have old plaster or render. There are no visible damp problems with the wall. I am going to hang radiators in the rooms and put some wires in -- therefore i need to create a void in which to do this.

The solution that has been recommended to me is to put up a metal frame on which to hang the plasterboard and run my pipes and wires within the void between the frame and the wall. Apparently I don't even need to remove the wallpaper or old plaster (is this right???)

Then I need to put a rockwool type insulation in the void and finally dryline/plasterboard onto the metal frame. Finally, I should skim the plasterboard to get the best finish.

Please note that I am based in France and I am constrained by the materials available there...

Can anyone tell me if they forsee any fundamental problems with any steps of this solution? E.g. Could there be problems with water damage or breathability or something (given that it is a stone wall), especially if skimming the plasterboard afterwards? Would I need some kind of airvent? Would appreciate the advice. Thanks

first up, dont use rockwool... it'll get damp, then slump and youll have a big wet mess at the foor of the wall smelling of cat er... urine....

you can get hold of cellotex equivalent down the bricomarche or other similar depo but it aint cheap, prolly double what it is over here... however, plasterboard is cheap enough and so is metal gypframe... timber isnt....

with them being the real thick, lime / mud mortar stone walls you get in france i'd suggest you build a 'studwall' out of gyprame, maybe 50mm in front of it, giving you a 50mm gap, that should allow the wall to breath better, if you can introduce airflow into it, it should be better off for it...

now you could strap something across the back edge of the gypframe to stop the cellotex boards falling through and insulate between the upright studs to thickness of the studs, then, if you want some more, go over the top with a thinner cellotex, say 25mm...

either way, you need a vapour barrier...

if you insulate between the studs only, youll need to install a plastic sheet over the entire wall, taping it round any holes where the sockets are going to be or if you install 25mm insulation over the whole lot you can just tape up the joints with gaffer tape, or plate closure tape - whatever...
or use 'duplex' (foil backed) plasterboard (better still, both)

the vapour barrier is to stop warm moisture laden air from WITHIN the house - washing machine, tumble dryer, shower, your breathing etc permeating the plasterboard and insulation and condensing on the cold wall behind...

screw the plasterboard to the studs, going through the insulation if youve gone 25mm over...

then either tape and joint it, or plaster it with a one coat plaster avaliable over there....

ask for lutec 2000 L or lutec 2000 C if you wanna plaster it, its a one coat machine plaster, youll need to treat it as such and use a sponge to liven it up again once youve got it on and laid down... then trowel up the fat, the finish is slightly softer than british gypsum multi finish or board finish but it does the job pretty well... its not cheap though... and its in 40kg bags...

they do do other one coat plasters but the set time on em is pretty quick - 40mins, so youll need to be pretty fast over large areas, but its doable...

ive been and seen these french stone walls and worked on em, so I understand your plight, especially with the materials, but if you check on the uk expats forums ('total france' i think ones called) you might find someone shipping british materials over there... there is a bloke somewhere in the northern(ish) part of france doing just that, but i cant find his number at the mo, ill see if i can root it out...

if youve got metres and metres and metres of it to cover, it might just pay you you ship a containerful of plasterboard, cellotex, screws, in fact just about everything youll need, over there... the prices of some stuff is shocking... the skirting board (well if you can call it that) is crap, same with the architraves - they dont use em over there... the stuff youll find is made up of lots and lots of smaller peices all glued together and is about 8mm thick...

plasterers over there arent cheap either..... (artisans) they love their externals - rendering, thincoat tyrolean type finishes etc but the internal plastering that i saw was absolutely...well...... lets call it 'olde english' so when you find a good 'spread' expect to pay silly money...

my advise - tape and join or get a bit handy with the one coat, it aint too difficult if you use the 2000L (its got a 2 hour set time) and a sponge with a garden water sprayer... and a good trowel

_________________
http://www.peterborough-plasterer.co.uk/

remember now, the cheaper 40 minute set plaster is called 'special finition'

lutec is spelt 'lutece'

numbers for uk builders merchants in france...

0673 680 572
0689 719 449
0633 295 788

_________________
http://www.peterborough-plasterer.co.uk/

Ok -- Thanks for that... looks like I can't just use the stuff they supply in the shops there...

yeh, you can, they do cellotex equivalent, have a look on the bricomarche website..

stuff i saw was only 2 foot x 8 foot sheets though if i remember, 50mm thick about the same as an 8x4 sheet over here...

its a phenolic insulation board, silverfoil covering a greeny yellow foam insulation core...

12.5mm plasterboard will be tapered edge...
its not too bad pricewise...

tape and jointing the boards will work out much cheaper cos the one coat plaster is bloody expensive...

the gypframe metal stud isnt too bad either for price...

but like i said, if you got tons of it to do... might be worth seeing if you can at least get the cellotex shipped over, its nice and light so might work out pretty cheap with a carrier company..

_________________
http://www.peterborough-plasterer.co.uk/

maybe not check the website, i couldnt find it, but i know its in the catalogue... might have to find a local store, its like their b&q...

_________________
http://www.peterborough-plasterer.co.uk/

Hi -- Thanks for you reply again...

I have another question: How important is the vapour barrier? I have heard a lot of different opinions concerning vapour barriers.... for example, they can trap moist air internally and cause damage that way... or that it does not let an old stone building 'breathe' when you cover the wall with plastic sheeting...

I have a couple of rooms that seem to have already been insulated with plasterboard and some kind of rockwool slab type material and that does not have any vapour barrier (but the room is also unheated). Do I have to rip off all the plasterboard and put in plastic sheeting or can I do something to the plasterboard to create a vapour barrier on the plasterboard itself?

ok...
warm air carries moisture... cold air carries much much less
the gap created between wall and insulation will be cold...
or cool at the very most...
in the winter for example, if you heat the inside of the building and introduce moisture into the air, it will be held in the warm air...
if this warm air then comes into contact with a cold surface then a dew point will be reached and the water contained in the air will 'condense' on the cold surface... such as a single glazed window..
the method i am suggesting is creating a 'cold wall' air gap, and as i suggested, you'd be better off ventilating this gap... how you do this is up to you...
the reason I suggested this method is down to the thickness of these stone walls, theyre about a foot to 18 inches thick yes? and prone to damp if they cant 'breathe' properly..

if this were a single skin brick wall in the uk what id do is stick the insulation directly over the brick, batten over the top after taping any joints, thus creating a warm air gap then plasterboard...

ive never heard of a vapour barrier paint, something you can apply to a plasterboard after the event...

these rooms you state, if you know theres rockwool behind the boards, then you must have already ripped off the boards first or am I missing something?

rockwool as far as i know isnt vapour proof...

if you manage to ventilate the cold air gap behind any kind of insulation sufficiently so that you have a clear flow or air, then a vapour barrier becomes less important as the warm air permeating through to the cold area will be ventilated out to atmosphere, think of a loft or attic with rockwool insulation and standard plasterboard....
if the said attic (known as a cold roof) is not sufficiently ventilated then any moisture produced within the house will permeate the plasterboard and insulation and condense on the underside of the roofing felt, the rafters, anything cold... causing problems like rot...
if you ventilate this space at eaves level (both sides) and preferably the ridge too then this problem is all but eliminated...

it depends on how much moisture is generated within the building, the temperature of the air, and the relative temperature of any surface this air is allowed to come into contact with...

the catch all solution is to ventilate any cold spaces, and seal them from any warm spaces by the use of a vapour barrier...

_________________
http://www.peterborough-plasterer.co.uk/

another option is to sufficiently ventilate the room itself, getting rid of any moisture in the air before its got a chance to build up an permeate the boards and condense on the wall behind...

as long as theres little moisture in the air, theres little chance of condensation....

put extractor fans in the kitchen and bathroom, open the windows, fit passive air vents, theyll all help to combat the problem....

_________________
http://www.peterborough-plasterer.co.uk/

I can see the rockwool behind the plasterboard cos I have taken a small section off the bottom... Ok... so it seems that a vapour barrier is less important if there is a flow of air in the insulation or if the rooms themselves have a similar moisture level to outside (i.e. the rooms are well vented)... but to be on the safe side it's best to have a vapour barrier. Can you recommend a product that I can buy in France in order to create this vapour barrier (I already have a load of plasterboards so an integral solution is too late)? Obviously the lower the price, the better...

I honestly have no idea what you could put over the plasterboard to create a proper vapour barrier... if theres no sign of condensation in this room at the minute, and the bit youve removed doesnt show any mould or algae growth on the wall behind, then I'd suggest you just ventilate the room and try not to introduce any excessive moisture into it..
its when you do introduce excessive moisture that the problems start..
you can purchase passive air vents online, ship them out, theyre a good solution to combating existing problems and may well do the job youre after without you having to touch the insulated walls themselves... passive air brick, passivent
gonna be fun getting it in an 18" thick wall made of pig stone which in my experience is silly hard stuff, but then again the mortar is really soft.... but harder things have been managed before...
If its the same stone I came across, you can hit it with a hammer and it just goes boiiinnnngg... proper hard stuff.... but a good long extension on a 110mm diamond core drill should cope with it once youve got it started...

you could do the same thing in every room except the kitchen and bathroom where it would be best to fit mechanical extraction, timed (run on) in the case of the bathroom, due to the likely high levels of moisture generated..
being as the windows in france tend to be of the open in variety, im not sure if theyre as secure as say a british open out fanlight that you can lock in 'night vent' position.... but then, maybe thats why the french love their shutters so much?



on the rockwool point, slab insulation of this type can be used but you must stop it getting damp...
the idea with the phenolic (synthetic foam insulation) board is its easy to cut and install, remains rigid, doesnt absorb moisture and has a very high insulation value per mm thickness (low u value)

to achieve the same using rockwool, you a) have to keep it dry (ventilated), b)have to support it properly and c) youll need 300mm or so as opposed to say 80mm of phenolic board...

choice is yours, i know I'd use cellotex just cos its what im used to but if you want a greener solution by all means use the rockwool but just make sure you follow its recommended installation procedure..

you can even use manufactured sheepswool slabs....

its the cold winter months where youre likely to have the biggest problem...

as far as im aware, in france the same 'building regulations' we have in the uk dont apply, its a case of applying to the mayor if you want to build a house and just get on with it...

try looking at different insulation companies websites, theyve usually got some form of installation examples....

good luck with it, especially being in france, it can be a bit of a mare getting hold of what you need, be prepared to travel a bit and pay a bit more but thats half the fun i suppose, bit of a challenge...

_________________
http://www.peterborough-plasterer.co.uk/