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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    We're finally at the decorating stage with our Cross Laminated Timber structure and approaching the inevitable question of how to line the wet room walls.

    I know some here favour whiterock style panels, but I think we're settled on larger format ceramic tiles for the finished surface.

    Wondering what the forum thought about substrates though. I've seen a few old threads talking about MR plasterboard or Kerdi membranes. My antipathy towards plasterboard means the current thought was a tilebacker board like HardieBacker on 10mm battens just to allow a drainage gap behind the substrate (we have wall brackets holding the CLT together so any substrate will be stood off the wall face anyway).

    My worry with the tilebacker is just mounting things onto it - are there different strength/thickness boards for heavier items? Do we need pattresses for shower units etc.?

    Also, what to do at the edges and base. Is it worth a sacrificial coat of something water repellent onto the timber behind as a second layer of defence, or would that just risk trapping moisture in the wood?

    Thanks in advance.
    • CommentAuthorBeau
    • CommentTimeJun 21st 2018
    • CommentTimeJun 21st 2018
    If you wanted I'd guess you could get away with leaving the timber exposed even in the shower, providing you have MVHR (or at least continuous extract from the shower room).

    The tile backer boards are quite strong and there's not much that's heavy unless you're wall-mounting basins and/or WC. The strongest mount we needed was for a handhold in the shower and we didn't put anything special behind to strengthen it. Certainly don't need anything extra for a shower.
    Thanks for the swift responses.

    We are ventilating with MVHR but the timber is literally just raw unfinished spruce so I'm wary of leaving this exposed, particularly as there has already been some shrinkage around panel joints etc. We've also got enough uncovered wood elsewhere that I don't mind losing the wood in this room.

    Ideally this will just be a 'fit and forget' one-off invisible job, but I want to be confident we aren't sealing in a problem.

    Beau, thanks for the Mapei link. This was my first thought but I wondered about guaranteeing the thickness of coverage vs. a self-adhesive membrane approach. On the plus side, I guess it wouldn't have the risk of tearing etc.

    How did you apply the gunk? Is it the stuff that goes on blue so that you know where you've been?
    • CommentAuthorCWatters
    • CommentTimeJun 21st 2018 edited
    Real HardiBacker board from James Hardie comes in at least two different thicknesses, 6mm and 12mm. The 12mm is much more robust than the 6mm or so called waterproof plasterboards.

    We have the 12mm on stud walls holding up thick travertine including in the shower itself. The SS brackets for our frameless shower are fixed through the stone into the backer board as are things like soap racks. The shower door hinges however are fixed to a brick wall so can't tell if they would be ok.

    I think it would be plenty strong enough to fix most things you might want to put in a bathroom except perhaps really heavy "kitchen" size wall cabinets - but you would use noggins in the wall or a board fitted to the wall where those are going normally.

    The 12mm HardiBacker is quite difficult to cut. Our builder used loads of blades in a jigsaw to cut it to size and they blunted quickly.
    • CommentAuthortony
    • CommentTimeJun 21st 2018
    Why use tiles?
    Posted By: tonyWhy use tiles?

    To be quite honest it's mainly just about aesthetics - despite all the talk of mounting this on a veneer of moisture resistant board, we've mainly managed to stick with self-finished or traditional materials throughout the rest of the build.

    I've always been a sucker for a decent tile and can't quite abide the idea of a vinyl printed imitation board or similar instead.

    I'll probably regret it when I'm scrubbing mould out of the grout in a few years time but for now I think it's what we're going to aim for.
    Posted By: CWatters
    The 12mm HardiBacker is quite difficult to cut. Our builder used loads of blades in a jigsaw to cut it to size and they blunted quickly.

    Thanks for the tip - I'll make sure we get lots of spare blades.
    • CommentAuthorBeau
    • CommentTimeJun 21st 2018 edited
    Posted By: Doubting_Thomas

    How did you apply the gunk? Is it the stuff that goes on blue so that you know where you've been?

    Not certain it was that brand but the description looks the same. It's gungy thick old stuff and no doubting where you have been. Think I used an old stiff bristled brush but cant be sure as it was long time ago.
    In our bathrooms and wet rooms we used 12mm Hardie Backer board which we had Venetian Plastered as the final finish.
    We used multi panel, which is ply with a waterproof printed plastic surface. It has lasted better than the tiles we used elsewhere, which are now showing a few chips and grubby grout lines, this was a good surprise to me as I was doubtful before.

    Multi panel apparently doesn't need a backer board, you can fix it straight onto the wall studs, although we already had plasterboard so stuck it onto that. It doesn't require tiling skills so might suit DIYing. Being ply, it is easy and strong to fix fittings to it.

    Only problem is that silicone sealant beads have not stuck well to the plastic surface, should have roughened it before sealing round the bath.

    Edit- I got the product name wrong:sad:
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