another isolation question

[shimble]

looking through various sites for isolation i need someone to verify a couple of points: when dealing with exterior walls that are humid, one needs to leave an air gap between the wall and the isolant(laine de verre) this can be further protected with a film of plastic that breathes, between the air gap and the isolant. if anyone can offer any thoughts on what  this plastic film is, and where it can be obtained. and how it is fixed it would be appreciated or any other thoughts on acheiving an insulated wall without the problem of moisture transferring though the wall and onto the isolation will be much appreciated

[Dave&Olive]

hi

 ok can we ask what you are going to build the stud walling with  metal lathe or wood studding ?

 dave

[shimble]

i was hoping to hold the plaque au platre using the metal framework but i am unsure whether i need to fix a wooden frame to the wall (to create the air space and if necessary fix my fil of breathing plastic that i can only find vague references to),behind the metal framework

[cooperlola]

You might also consider using placaux (sp?) marine (the green stuff) which is designed for bathrooms etc?

[Chancer]

I had a similar problem with the exterior wall of the flat that I have recently built, the outside ground level is nearly one metre up the wall, the old polystyrene backed placo was dot & dabbed to the wall and was covered in mould and the polystyrene had decomposed into granules.

I did some work to mitigate the damp passing, it is a tennis court adjacent and I infilled the gap with an angled fillet of concrete to prevent it being a gully but none the less the wall is still significantly below the water table, before the placo went up the bottom of the wall was always damp.

I used metal rails but due to the lack of space they are nearly touching the wall, I used expanded foam between the raiul and wall to add rigidity so there is in fact a contact path for moisture, then I used 45mm paper backed lain de verre with the glass face to (and of course touching in many places) the wet wall. Finally I finished with greem M/R placo for added insurance.

It was left unfinished like this for about 6 months without any sign of  moisture transfer, I have now decorated the walls, have storage heating and am living in the flat, outside it has been very wet for what seems like weeks now.

I have no trace or smell of damp on the wall but I do have a hygroreglable VMC that vents from the adjacent kitchen area.

Given that I arguably had a very bad damp problem (and indeed still will have behind the placo) I am very pleased and convinced with the metallic rail/air gap method especially as I havn't in reality got the airgap working for me.

[shimble]

i was talking to someone today who suggested the polysterene backed plaque au platre as opposed to rockwwool laine de roche, his argument was that the laine de verre/roche will tend to absorb the moisture and my damp which is mainly a condensation problem will continue behind the plaqe ( not sure if ive explained this how it was explained but....) however he proposed that with the polysterene backed plaque the damp would not be absorbed by the polysterene reducing the transfer problems from the wall to the inner wall, yes i was hoping to use the green plaque, does this come with the polysterene attached? however reading the above about the breakdown of the polysterene behind the wall leaves me again confused and unsure as to how to proceed, any ideas or thoughts?

[Chancer]

The damp had certainly came through the polystyrene backed placo and had gone on to degrade the polystyrene.

The laine de verre revetu has a paper coating which is in fact waterproof, this is the face that you put against the placo, I found this out when I stored the panneaus in my greniere and the roof leaked, a week later I found  puddles of water on the paper but it had not passed through. Remember this was horizontal, you will be using it vertically.

If you have the space ust the meatl rails and also try to leave a "vide d'air" if not do it as I have and I am sure you will have the same success.

[andyh4]

The breathable plastic membrane is available from a number of sources.  The best known is called Tyvec and is made by DuPont.

[shimble]

merci pour les info's i think i shall come back later to question differnt methods of insulation as i am trying to decide between laine de roche laine de bois, polysterene and the air bricks or a mixture of would be interested to hear thoughts and experiences from people who have experience of all methods. whether they be negative or positive my main criteria is to combat problems of condensation obviously have a warmer house but also have a system of insulation that will not deterioate over the years as i really dont think i will be to keen to redo it all in later life anyway thanks for your observations hope your all lapin's content.