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    • CommentAuthorAis
    • CommentTimeJun 10th 2008
    I have a 1st floor bathroom with one external wall.
    The whole bathroom has been ripped out down to the brick and is about to be redone.
    i thought I would take the opportunity to insulate the external wall (discussed in a previous thread "mixing internal and external insulation")
    i was going to use Knaupf phenolic laminated plasterboard with vapour barrier, 50mm but their technical line has advised me it's not suitable for bathrooms due to the possibility of moisture ingress. The same goes for their polystyrene boards. They stick to this advice even though the board will be coated with 2 layers of wallboard primer and fully tiled, grouted, etc.

    Question: is this the company over-covering themselves or should I take their advice?

    I am having a false, plasterboard ceiling put in to the bathroom. Above the real ceiling is eaves space, insulated (thinly) with mineral wall at both floor and roof level. I'm worried, having read a thread from July 2007 about insulating a bathroom, that I might get trouble with moisture ingress and condensation into the layer between the false and real ceilings.

    Question: should I be worried about it, or is it likely to be warm enough/moisture proof enough?

    Many thanks for any insights.
    • CommentAuthorjamesingram
    • CommentTimeJun 10th 2008 edited

    If I was doing the job I'd not worry about water ingress with your wall , you can get tile backer board made out of a similiar stuff so I'm not
    sure what the problem is. forget the wall board just use something like this.
    and as to condensation in your loft if you put a vapour control layer ( cheap thin polythene sheet ) above the plasterboard and try to join it to the VCL
    on your walls , that will help , making it as airtight as possible, it should reduce any possible problem.
    I'm no expert by the way, just never experienced condensation problems in such situatuions , the main trouble is a long term solution to the junction
    where bath or shower tray and wall meet and mouldy grout due to lack of ventilation etc.
    • CommentAuthorAis
    • CommentTimeJun 10th 2008
    Thanks James, I've looked at that site and might go for that.
    It keeps occurring to me, however, that surely the tiles form a vapour barrier in themselves (provided properly grouted and siliconed)?
    • CommentTimeJun 11th 2008
    Maybe you shouldn't think of the wall on its own, since its moisture / vapour barrier is unlikely to be contiguous with what's underneath the floor, for instance. Thus moisture ingress is possible not just from the bathroom itself but from the air in the house generally - and may condense behind the wall panels leading to hidden mould etc.?
    • CommentAuthorAis
    • CommentTimeJun 11th 2008
    Oh dear, that sounds like a problem for internal insulation in general.
    Hi Ais,

    I was just wondering what solution you went with? I'm about to internally insulate a 1st floor bathroom with 3 external walls and I'm keen to hear what experiences other folks have had.

    I'm tentatively planning to use Kingspan (laminated with pasterboard) glued onto the existing walls and tiled. The bathroom will have a mechnical ventilations heat recovery unit. I haven't spoken to Kingspan yet to ask if this is an acceptable application of their product.

    Many thanks,
    Back in the 'old days', when I did this house - 20+ years ago when styrofoam was blown with CFCs (sob) and we were told the closed cell format of the foam was enough of a VCL, I did not use pl'bd for walls I was going to tile - I just tiled onto the styrofoam (extruded poly). After 18 yrs I re-jigged the shower room. No probs whatever. I moved the shower and needed plasterboard where the tiles had been, so I just glued it on. I wiiiish I'd had a crystal ball, though, and striven for 0.2 instead of 0.5!
    • CommentAuthorSaint
    • CommentTimeFeb 5th 2009 edited
    Jamesingram is correct. Go for a tilebacker board but he's wrong in saying its phenolic. Most good tilebacker boards are based on extruded polystyrene (XPS) that is impervious to water and moisture pick up. Available in a range of thicknesses they provide both the insulation and a strong substrate that can be tiled on directly.
    Best known is Wedi from Germany although there are boards coming in from Egypt that seem to have an unrealistically high thermal value. That suggests that they have not allowed for the reduction in thermal value when slicing a thicker XPS block into thin sections or the boards have been tested to a standard either not relevant here or just outdated?
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