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Celotex without battens

Discussion in 'Building' started by motorbiking, 1 Dec 2020.

  1. motorbiking

    motorbiking

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    I'm about to decorate a room, the Last downstairs room in our house which doesn't have modern insulation (9" brick without cavity). I plan to take the lime plaster back to brick and replace with 50mm celotex with plasterboard on top. I don't really want to use battens.

    I was thinking of using a foam dry fix adhesive to attach the celotex and then the same to attach the plaster with a few frame fixers. Celotex plasterboard backed insulation is very expensive.
    GA4050 is £20.50 per sheet
    PL4050 is £47.00 per sheet
    I appear to be paying £20 a sheet for them to attach the plasterboard.

    anyone any experience?
     
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  3. ^woody^

    ^woody^

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    Nah. 50x25mm battens every 600, cheap hammer fix and screws, celotex between and 25mm over the battens and then screw the plasterboard to the battens. It takes no longer and is an overall better job, secure, with no risky air voids.
     
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  4. mrrusty

    mrrusty

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    You may find this helpful https://www.siniat.co.uk/en/downloa...97.1777513509.1591631637-442191837.1591097244

    Note they suggest that direct fixing insulated PB is not recommended for solid walls, and if installing to solid walls a minimum 25mm cavity is suggested. I agree with this - I think you need the air space between the insulation and a solid wall, and I wouldn't internally insulate at all if teh solid wall is rendered or coated on the exterior - interstitial condensation has to have the chance to evaporate. My 2p.
     
  5. SFK

    SFK

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    Following Woodys good suggestions.

    Also need Aluminum tape to tape the joins of the Celeotex sheets together to reduce air/moistrure flow.
    Don't buy from screwfix (it was not Aluminum tape, but coloured sellotape), buy from Toolstation.

    With regards to the Hammer fix, I pushed batten against the wall and used a Masonry drill bit through the wood and into wall in one go.
    Put hammer fix loosely into hole to hold batten in place.
    And then moved down baton repeating process.
    Might not be good for a masonry drill bit, but made process much much faster.

    Only issue I had was that 50mm Celotex sheets were not flat, but had a 1cm curve accrosss them.
    Had to put spaces behind batons :<

    SFK
     
  6. motorbiking

    motorbiking

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    I think I may go with the idea of 25 x 50 battens, cut each 50mm board in to 2 x 600mm and recess 25x25mm at each edge to cover the batten. Rather than use 25mm celotex x 2 and overboard one.
     
  7. SFK

    SFK

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    Making a L shaped recess sounds a nightmare of fildyness and a lot of time. I found cutting celotex to that level of precision near impossible.

    But agree that buying two thicknesses is a stock control issue.
    I now have a coupe of left over sheets (and all the offcuts taped together) under the insulation in my loft.

    Using your idea - how about this....
    -Use 25mm deep batons.
    -Put 50mm sheet between batons (no L shapped recess in sheet).
    -Buy one additional 25mm sheet (or cut a 50mm one through the middle), and make long narrow (50mm) lengths to cover the batons.
    -Tape all together.

    Much faster and less fiddly.
    SFK
     
    Last edited: 2 Dec 2020
  8. motorbiking

    motorbiking

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    If I do that I will have to cut 50mm off each panel anyway.
     
  9. Djangobanjo

    Djangobanjo

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    I used 50mm insulation with plasterboard stuck on. Stick the insulation up, then stick the plasterboard onto that. Chuck in some mechanical fixings if you don't have complete faith in adhesive. Everbuild dry fix pink foam. Follow the instructions! ie spray on in lines, creating a border then lines about 6-9 inches apart, wait 4 minutes, push onto wall, apply pressure.

    If you are used to using plasterboard adhesive it will probably seem like a horrible way to do it, with lots of waiting. Time it right and it will not come off.

    Benefits are, you can fully cover the wall in insulation and then seal with silver foil tape to create a vapour barrier (insulation boards have silver barrier front and back too, bonded boards don't tend to have any), and then board over. Better result and easier to work with.

    I didn't use battens in my house as I was concerned about them rotting (we had lots of rot and mould) and I didn't want to lose any more room than needed.
     
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  11. motorbiking

    motorbiking

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    Yeah I'm trying to avoid the cost of the insulated plasterboard as its more than twice the price. Never used to be.
     
  12. mrrusty

    mrrusty

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    Yes they do "GTech Thermal PIR and Thermal K boards have a metallised vapour barrier provided as standard"

    I do not understand why people are still suggesting insulating between the battens, when the suppliers of insulated PB onto solid walls state "allow for required cavity of at least 25mm". Not saying I'm an expert, but I do tend to follow manufacturers installation instructions.
     
  13. ^woody^

    ^woody^

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    Its easy.

    With a normal wood saw, cut the 50mm celotex into a 50mm strip, and then it can be cut down the middle to give two strips with a silver face.
     
  14. SFK

    SFK

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    Woody,
    That was my sugegstion.
    My "nightmare of fildyness" was at his idea of cutting a 25mm by 25mm L shaped cut in the edge of a sheet to cover the baton.
    SFK.
     
  15. ^woody^

    ^woody^

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    OH I see, I misread it. :oops:

    I have actually tried that L cutout thing, and whilst it can look a bit better (not that it matters) it is fiddly with no real advantage.
     
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  16. mikeey84

    mikeey84

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    The instructions for installation of celotex pb laminates say that it can be bonded directly to the wall using plaster dabs.

    I've not checked Kingspan, but I imagine they would say similar...
     
  17. catlad

    catlad

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    Yes proper insulated pb can be dot and dabbed, that is why it only has foil on one side. introducing timber to a solid wall sound like a time bomb.
     
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