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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorLoftDIY87
    • CommentTimeJun 29th 2020
     
    I have a studded bathroom with 90mm insulation between studs and 15mm insulation over the studs, which I intend to board and fully tile.

    Want to fit 12mm Hardiebacker board in the shower area and 12.5mm moisture plasterboard on the rest of the walls, then tile.

    Just called Hardiebacker and they said their boards should only be fitted direct to the studs, NOT have any insulation in between (even if only 15mm)? As they can't guarantee it'll hold the weight?

    How can this be dealt with? Would the same issue not arise when plasterboarding over the 15mm insulation and tiling on top?

    I would have thought long screws were the answer but now am a bit confused on which direction to go, any guidance?
    • CommentAuthorphiledge
    • CommentTimeJun 29th 2020
     
    If you can reuse the 15mm insulation then take it off and use Jackoboard or similar. Id be fairly certain Hardiebacker are advising to fix direct to studs as that will be the build they have tested and proven to work. There will be a multitude of scenarios like yours that they havent tested so they cant approve, but its not to say it wont work.
    • CommentAuthorLoftDIY87
    • CommentTimeJun 29th 2020
     
    Thanks...have already fitted the 15mm insulation and already purchased the Hardiebacker and moisture resistant plasterboards ready to fit, so ideally want to make use of them all.

    If I did buy Jackoboard/Marmox instead to use in the shower area, what about the rest of the bathrooms external walls, where I was planning to put moisture resistant plasterboard over the 15mm insulation, and tile over? Or would I have to put Jackoboard on ALL external walls instead?
    • CommentAuthorphiledge
    • CommentTimeJun 29th 2020
     
    Personally, Id only use jakoboard/hardie backer board where there was a risk of water ingress, so just in the shower area and a touch to the sides of it. For the rest of the bathroom Id just use ordinary plasterboard.

    Through lockdown Ive converted a tired 20 year old ensuite into a wetroom and the standard plasterboard within the tiled shower area was in serviceable condition except for a bit of water ingress around pipe penetrations and one screw fixing. Id have no issue with using std board outside of wet areas.
    • CommentAuthorFred56
    • CommentTimeJun 29th 2020
     
    Perhaps ditch the tiles. Horrible things with porous grout. Go for a sheet material, wet wall or whatever.

    Ref insulation over the studs. I built an entire 4 bed house with 50mm over the timber studs (Rockwool Flexi between) and a huge brick barn conversion (265sqm) nearly twenty years ago too. I was using Fermacell in the all areas even vaguely damp and everywhere with anything weighty hanging off the walls. No problems to report.
    • CommentAuthorLoftDIY87
    • CommentTimeJun 29th 2020
     
    Definitely can't ditch the tiles, the Mrs has already chosen them :neutral:

    Surely plasterboard manufacturers would have specification on what thickness, if any, PIR insulation can be put behind their plasterboards when tiling over?

    Wouldn't insulation behind plasterboards be a common occurrence or is EVERYONE using cement boards in bathroom installations!

    Might ask BC officer although doesn't really fall under BC. Really don't want to go out and purchase new materials when I already have the Hardiebacker, moisture resistant plasterboards and already neatly cut and fit the 15mm PIR (around pipes too :angry:)
    •  
      CommentAuthordjh
    • CommentTimeJun 29th 2020
     
    Moisture resistant plasterboard is a pretty cheap way of getting a noticeably better performance, so I would use it rather than ordinary plasterboard. But I expect the ordinary stuff would be OK.

    I agree with Fred about the surface treatment. My wife hates cleaning grout so we have no tiles and went with sheet surfaces everywhere. They're a lot better than they used to be.
    • CommentAuthortony
    • CommentTimeJun 30th 2020
     
    +2 for panels = fail safe
    • CommentAuthorphiledge
    • CommentTimeJun 30th 2020
     
    If youre insulating behind tiles on internal and external walls, the walls are likely to stay warmer and water will dry quicker. If you wipe down after showering with a window cleaners wiper youll get most of the water off and tiles will be dry in no time. This should keep any mould in check........ having insulated our internal walls and wiping down, we're hoping so!!
    • CommentAuthorowlman
    • CommentTimeJun 30th 2020
     
    + 1 for panels, or, if you've got bottomless pockets, and the tools to handle them, extra large format tiles, up to 8' X 4'. As others have said small ish tiles are out AFAIC. I've just re lined my shower with good quality plywood backed sheet and anodised aluminium trims and it looks the bee's knees.
    • CommentAuthorJeff B
    • CommentTimeJun 30th 2020
     
    LoftDIY87 - I have used Hardibacker board for the walls of a shower enclosure, admittedly not with insulation behind as the walls were both internal. However I really cannot see why, with sufficiently long screws, you cannot use the Hardi board in your situation.

    OK the stuff is heavy but if the bottom sheet is resting on the floor then the screws are only keeping the board in place rather than taking any weight. Celotex is not easily crushed, so there is no fear of the Hardi board cracking as you tighten the screws – maybe don’t over-tighten though, just tighten by hand for the last few turns?

    Re tiles vs sheet material. I have always gone for tiles but I think if I ever did a shower enclosure again I would opt for the latter. We use one of those Karcher window cleaning suction gadgets and it is brilliant at keeping the grout clean but it is quite a faff to use – probably takes longer to dry the tiles than to have a shower!
  1.  
    I'm big fan of shower panel board as I don't like cleaning grout myself. And it's easier to DIY than tiles are, especially if the wall isn't too wavy .

    The ones I have done, used adhesive to fix the shower panel. Not sure if this would work well with insulation between panel and studs (maybe works?). We put insulation over studs on external wall, fixed moisture resistant plasterboard with screws through, then glued the panel to the plasterboard (maybe overkill?)

    Why is moisture resistant plasterboard so much more expensive than normal pb?
    • CommentAuthorCranbrook
    • CommentTimeJun 30th 2020
     
    If you are using Hardie backer on wet areas you should still fully tank the Hardie backer (either with a taking paste or tanking membrane) as it's water resistant only, not water proof. If you use a XPS board such as jackoboard or wediboard etc then these are waterproof and only need tanking at the joints (with a tanking tape). As you've got some Hardie already, grab yourself some jackoboard washers and just go overboard with the fixings through the insulation you have and in to the studs behind.. Hardie won't guarantee the work but you should be okay with a common sense approach

    With regards to the rest of the walls that you plan to tile, personally I would not waste your money on MR boards and use standard boards instead. I only use MR boards for ceilings in bathrooms and for any walls that aren't to be tiled. And then taping and jointing instead of plastering as they're not designed to be plastered
    • CommentAuthorCWatters
    • CommentTimeJun 30th 2020 edited
     
    We have 12mm Hardi holding up heavy Travertine stone (not tiles) and no tanking. Been up 13 years in a shower used 4 times a day.

    12mm Hardie is pretty strong stuff. I reckon if the bottom edge is resting/supported on the floor and its well screwed to the studs through the insulation it will be fine. Compare with Wediboard which is a light foam insulation covered with a thin fibreglass mesh stuck on with cement. If that can hold up tiles or stone then Hardi jolly well can. I used Wedi on the washbasin stand also covered with travertine.

    We also screwed soap dishes and handheld shower brackets to the Hardi through the stone (eg not into studs). Its much nicer to fix to than regular plasterboard.
    • CommentAuthorCWatters
    • CommentTimeJun 30th 2020
     
    Not sure i'd use it over screws but whats this stuff? Looks like an adhesive for fixing Hardie Backer board to insulation (among other things) prior to tiling...


    https://www.ctdtrade.co.uk/preparation/tile-backer-boards/hardie-backer-fixing-foam

    Quote..

    Hardie Backer Fixing Foam
    D0008368
    Type: Board Adhesive
    Brand: James Hardie
    Size: 750ml

    Key Features: Ready to tile and plaster in 1 hour

    It can be applied on all common surfaces such as...... snip....insulation board..snip...polystyrene...
    • CommentAuthorCranbrook
    • CommentTimeJul 1st 2020 edited
     
    Posted By: CWattersWe have 12mm Hardi holding up heavy Travertine stone (not tiles) and no tanking. Been up 13 years in a shower used 4 times a day.

    12mm Hardie is pretty strong stuff. I reckon if the bottom edge is resting/supported on the floor and its well screwed to the studs through the insulation it will be fine. Compare with Wediboard which is a light foam insulation covered with a thin fibreglass mesh stuck on with cement. If that can hold up tiles or stone then Hardi jolly well can. I used Wedi on the washbasin stand also covered with travertine.

    We also screwed soap dishes and handheld shower brackets to the Hardi through the stone (eg not into studs). Its much nicer to fix to than regular plasterboard.


    Agreed, my past wasn't intended to say that unless you tank Hardie backer it will fail, same as thousands of bathrooms with just standard plasterboard etc haven't failed, it's just a belt and braces approach which is airways a good thing whene'er water is involved.

    The Hardie foam is good stuff, but I'd still washers and screws as well, again belt and braces. Same as when overlaying Hardie over floorboards, we always 'glue and screws'
    • CommentAuthorLoftDIY87
    • CommentTimeJul 1st 2020 edited
     
    Thanks for comments all.

    After all your input I think I will stick with the 15mm PIR behind Hardiebacker in the shower area and 15mm PIR behind moisture plasterboard in the other external wall areas. Seeing as I have already purchased these materials (and fit the 15mm PIR), will be a waste to redo it all if the current setup will still securely hold with long screws.

    Speaking of, would 65-70mm screws be OK? This would be 12mm through the Hardiebacker/plasterboard, 15mm through the PIR insulation and 38mm/43mm into the stud for 65/70mm respectively.

    These Turbo Golds for the Hardiebacker: https://www.screwfix.com/c/screws-nails-fixings/woodscrews/cat840066?brand=turbogold#category=cat840066&brand=turbogold&productlength=70_mm

    And drywall screws for the plasterboard: https://www.toolstation.com/drywall-black-phosphate-phillips-screw/p42417

    Re: Hardeibacker resting on the floor, they advise leaving a 2-3mm gap between boards and the floor, thus they wouldn't really be resting on each other and would only be fixed to the wall?
    • CommentAuthorCranbrook
    • CommentTimeJul 1st 2020
     
    I would make sure to at very least use some silicone over each screw that you use to fix the hardiebacker (in wet areas).

    Not quite sure what you mean about resting on the floor but I’m guessing you mean your need to pack the hardie up... ?
    • CommentAuthorFred56
    • CommentTimeJul 3rd 2020
     
    Hardiebacker has its own design of screw. I suspect they will be like a fermacell screw with a steeper countersink angle more suited to harder boards.
    • CommentAuthorCWatters
    • CommentTimeJul 4th 2020
     
    +1 Its pretty hard stuff. Think we used a combined drill and countersink bit.
    • CommentAuthorJeff B
    • CommentTimeJul 4th 2020
     
    Regarding expansion gap and not having Hardiebackerboards resting on the floor. The official Hardie video:

    https://www.jameshardie.co.uk/new-installation-video-installing-12mm-hardiebacker-onto-a-stud-wall/

    shows that it is ok to leave expansion gaps and still have a secure fixing to the studs, relying on screws alone, so I don't think you have any worries as long as you use long enough screws as you have already mentioned. 3" (75mm) should be ample!
  2.  
    I want to be using stainless steel screws for the tiny additional cost that they represent overall.

    Probably overkill though.
    •  
      CommentAuthordjh
    • CommentTime4 days ago
     
    Posted By: ealingbadgerI want to be using stainless steel screws for the tiny additional cost that they represent overall.

    I agree in principle but I would check what the Hardie warranty says about the use of their own screws.
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