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Housing - New Build: airtight adhesive

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      CommentAuthordjh
    • CommentTimeJul 9th 2014
     
    Not really a new-build only question but I didn't know where else to put it...

    We've found a place where as-drawn doesn't look ideal when it comes to actually build it. Each window sits on a piece of OSB (actually they are screwed to the OSB). The plan was to put an airtight membrane on top of the OSB and fancy tape the edge into the interior plaster under the window. The window board sits on top of the membrane. The difficulty is how to secure the window board?

    Screwing through it from the top is not appealing because of the difficulty of making the holes invisible in perpetuity. So we'd prefer the alternative method of gluing down the window board. But how can we glue the window board to the OSB, perhaps with an airtight membrane in between, in such a way as to guarantee airtightness?

    Is there some airtight glue? Or some airtight membrane that can be glued on both surfaces and still function?
    • CommentAuthorowlman
    • CommentTimeJul 9th 2014
     
    A couple of possibilities, building silicone or Butyl tape, (it's available in 2" wide rolls).
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      CommentAuthorfostertom
    • CommentTimeJul 9th 2014
     
    Why not trust the OSB and/or the cillboard to be robustly airtight without resorting to long-term (or even short-term) vulnerable fancy-tape and membrane?
    I like 'fancy-tape' - will use that one!
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      CommentAuthordjh
    • CommentTimeJul 9th 2014
     
    Posted By: owlmanA couple of possibilities, building silicone or Butyl tape, (it's available in 2" wide rolls).

    I have some 2" butyl tape but I'd need an awful lot of it! The whole area has to be airtight, not just some strips. So for the living room window alone that's about 250 mm x 3000 mm. I believe silicone is viewed as unreliable over time.
    • CommentAuthoralexc
    • CommentTimeJul 9th 2014
     
    The other standard approach i have seen is OrconF on top of membrane the screw down tight....
    mind you those who have been doing our place(including myself) have been taking a liberal approach to its use.
    The stuff is reall like tree sap, but just not as tenacious. Just sticks. to what goes through
    Where thats not been recommended. Nails. I have used annular nails as they are just hard to remove. But with that time will tell. They puncture the membrane not rip. And hopefully you have hit'em hard in.
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      CommentAuthordjh
    • CommentTimeJul 9th 2014
     
    fostertom asked:"Why not trust the OSB and/or the cillboard to be robustly airtight without resorting to long-term (or even short-term) vulnerable fancy-tape and membrane?"

    Err, you were involved in the thread about the leakiness of OSB weren't you? Ah yes: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361

    And whilst window boards may well be airtight, I doubt there's any proof!
    • CommentAuthorowlman
    • CommentTimeJul 9th 2014 edited
     
    Posted By: ............I have some 2" butyl tape but I'd need an awful lot of it! The whole area has to be airtight, not just some strips. So for the living room window alone that's about 250 mm x 3000 mm. I believe silicone is viewed as unreliable over time.



    Dave, This is the sort of stuff I had in mind, I don't know if Yours is the same.
    50mm x 1mm x 50M for £4.69 plus VAT each, for a dozen rolls doesn't seem too expensive if it does the job.

    http://www.psasolutions.uk.com/adhesive-tapes-and-glues/butyl-flashing-tapes/butyl-membrane-jointing-and-sealing-tape-psa302-detail

    Are you saying the whole 250mm width has to be covered? Couldn't you put say three strips of tape, perhaps with a bead of building silicone between. What material are the window boards?
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      CommentAuthordjh
    • CommentTimeJul 9th 2014
     
    Posted By: owlmanThis is the sort of stuff I had in mind,

    Yes, that's where I buy mine.

    50mm x 1mm x 50M

    It would be cheap if it was! The rolls are 10 m, not 50 m.

    Are you saying the whole 250mm width has to be covered? Couldn't you put say three strips of tape, perhaps with a bead of building silicone between.

    Exactly. It is the whole area that is part of the airtightness barrier. An application for membrane rather than tape. Or flood the whole surface with some glue or suchlike. I've just no idea whether something as simple as PVA would be airtight :cry:

    What material are the window boards?

    MDF. It seems to be the standard for functional reasons, unless you have a bottomless purse. Maybe the MDF is airtight, I don't know?
  9.  
    I used butyl tape as a gasket where I had to screw through the air tightness layer and just screwed the window boards at the very ends, the screw heads were then covered by the plasterboard. But I guess you are not using plasterboard!

    Given that it is MDF you are using I would just deeply countersink the screwheads and then fill over with a mix of PVA glue and saw dust, will never be seen again.

    [Edit] Likewise I thought that I would have to use MDF because I couldn't find window boards in the 30cm depth I needed but in the end found oak block shelves in a DIY shed that were perfect for the job @ approx. £18 a window.
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      CommentAuthorfostertom
    • CommentTimeJul 10th 2014
     
    Posted By: djhErr, you were involved in the thread about the leakiness of OSB weren't you? Ah yes:http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361" >http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9361
    Yes, and the point of that is that some of us incl Viking House have found OSB reliably airtight, despite what others say - and the manufs are taking the matter thoroughly in hand. The prize - no more tapes and membranes - is v valuable.

    If in doubt, why not paint on some sealer?
    • CommentAuthorowlman
    • CommentTimeJul 10th 2014
     
    If you have sufficient depth for the window boards why not put in a "utility ground" window board of plain MDF sealed, glued, screwed, taped; whatever. That would be the airtight seal. Then you could simply bond another decorative, veneered MDF or solid wood on top of it with a downstand lip to cover the ground beneath, and with no visible fixings.
    •  
      CommentAuthordjh
    • CommentTimeJul 10th 2014
     
    Posted By: fostertomYes, and the point of that is that some of us incl Viking House have found OSB reliably airtight, despite what others say - and the manufs are taking the matter thoroughly in hand. The prize - no more tapes and membranes - is v valuable.

    I agree about the value of the prize. I don't have any information about which brands of OSB are airtight and especially no manufacturers' certs. So what is and is not airtight and exactly what have the manufacturers done?

    If in doubt, why not paint on some sealer?

    Well, that is my question isn't it? Exactly which sealer are you claiming is airtight (and what is the proof)?
    •  
      CommentAuthordjh
    • CommentTimeJul 10th 2014
     
    Posted By: owlmanIf you have sufficient depth for the window boards why not put in a "utility ground" window board of plain MDF sealed, glued, screwed, taped; whatever. That would be the airtight seal. Then you could simply bond another decorative, veneered MDF or solid wood on top of it with a downstand lip to cover the ground beneath, and with no visible fixings.

    We don't have a lot of depth since the windows are internally opening. The idea of an airtight board rather than an airtight membrane is an interesting one though. MDF isn't suitable because that definitely is not airtight. But I'll measure how much room we do have and see whether I can find a thin airtight board.
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      CommentAuthorfostertom
    • CommentTimeJul 10th 2014
     
    Posted By: djhMDF isn't suitable because that definitely is not airtight
    Ah so - I never needed to ask that so far.
    Posted By: djhwhich brands of OSB are airtight and especially no manufacturers' certs
    As yet, no brands are definitely certified airtight - even varies from batch to batch, or at least they can't be sure. But fact remains that Viking House reports consistently gd results, and he builds a lot.
    •  
      CommentAuthordjh
    • CommentTimeJul 10th 2014
     
    Posted By: fostertomBut fact remains that Viking House reports consistently gd results

    Perhaps, but other people report problems, and problems have been documented in at least two papers. So as far as I can see the question is still open, and I guess that since you have failed to name any specific products you think so too, despite what you say.
    • CommentAuthorowlman
    • CommentTimeJul 11th 2014 edited
     
    Posted By: djh
    ...... The idea of an airtight board rather than an airtight membrane is an interesting one though. MDF isn't suitable because that definitely is not airtight. But I'll measure how much room we do have and see whether I can find a thin airtight board.


    What about phenolic resin coated ply? It's expensive but one or two 8 x 4s may suffice for all your windows.
    • CommentAuthorTriassic
    • CommentTimeJul 11th 2014
     
    If MDF is not airtight how about using a plastic window board or Formica?
    • CommentAuthorTriassic
    • CommentTimeJul 11th 2014
     
    Or Kronospan OSB Airstop board. http://kronospan.cz/en/osb-airstop/
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      CommentAuthorfostertom
    • CommentTimeJul 11th 2014
     
    That's right, coated OSB as a stopgap until the OSB manufs get their quality control in order, which I know Smartply for example are working on. But at premium price.

    It's a coating, so we just need to know what that is and paint it on either routinely, or the solution that others have used, when pressure test shows there's a problem.

    Glued and screwed OSB is so close to being the preferred reliable air barrier - cheap, foolproof, ordinary builders merchant source, standard skills, long term robust - all the opposite of tapes and membranes.
    •  
      CommentAuthordjh
    • CommentTimeJul 11th 2014
     
    Posted By: owlmanWhat about phenolic resin coated ply? It's expensive but one or two 8 x 4s may suffice for all your windows

    By my calculations I would need four sheets. So I suspect cost would be a showstopper. Also how do I know it is airtight?

    Posted By: TriassicIf MDF is not airtight how about using a plastic window board or Formica?

    The MDF boards are ordered. I could use Formica in between but is it airtight? Can I glue to it?

    Posted By: TriassicOr Kronospan OSB Airstop board.

    The OSB is already installed (Norbord SterlingOSB)

    I feel sure there must be some coating that wil do the job. I just need to find the specific item.
    • CommentAuthorTriassic
    • CommentTimeJul 12th 2014 edited
     
    Posted By: djhI feel sure there must be some coating that wil do the job.
    I've often wondered if a coating would work. It could easily be sprayed on at the construction stage.
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      CommentAuthordjh
    • CommentTimeJul 13th 2014
     
    Posted By: TriassicIf MDF is not airtight how about using a plastic window board or Formica?

    Ah hah! I know what is definitely airtight - metal. Even metal foil is airtight isn't it? And I can definitely glue it. So perhaps a thin sheet of aluminium might do the trick? Or even kitchen foil if I was very careful.

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