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  1.  
    Can anybody recommend a suitable detail for between lime plaster and timber windows? Between the window frame and the timber frame we have stuffed hemp wool very tightly. On the outside, the renderers used a stick on plastic frame with an attached mesh that is built into the render. Mostly this seemed okay, but in a couple of places they have come away from the window frame and been gummed up with render, so there is a gap of 1-2 mm that I will probably need to fill with sealant.

    We're wondering what to do on the inside to ensure it is as airtight as possible.

    The interior reveal angles are 22.5ΒΊ on the sides and 10ΒΊ at the top.

    I'd be very grateful for any comments.

    Thanks CoP
  2.  
    I should add that we haven't plastered on the inside yet.
    • CommentAuthorDarylP
    • CommentTimeFeb 12th 2018
     
    IsoBloco or similar tape, pull off the 'expanding' tape after the plaster has 'cured'...?
  3.  
    Thanks @DaryIP, that looks good for between the timber frame and the window frame, but we've already sealed that gap with the hemp wool (and the windows are in place). I'm looking for something that makes a nice airtight seal between the plaster and the timber window frame.
    •  
      CommentAuthordjh
    • CommentTimeFeb 12th 2018
     
    Contega PV is designed for exactly that purpose. It's what I used. Our reveals are curved. You don't need to seal to the rough frame since that is behind the airtightness barrier (assuming it is the window and the interior lime).

    Do make sure to apply plenty of pressure to seal the tape to the wood. You can use the neat little rubber rollers, or I used the back of a knife handle. You may find it more convenient to apply Tescon Profil to the window frame and attach the Contega PV to that, depending on the angles you need. i.e. do an experiment first.
    • CommentAuthortony
    • CommentTimeFeb 12th 2018
     
    Linseed oil mastic?
  4.  
    Posted By: djhContega PV is designed for exactly that purpose. It's what I used. Our reveals are curved. You don't need to seal to the rough frame since that is behind the airtightness barrier (assuming it is the window and the interior lime).

    Do make sure to apply plenty of pressure to seal the tape to the wood. You can use the neat little rubber rollers, or I used the back of a knife handle. You may find it more convenient to apply Tescon Profil to the window frame and attach the Contega PV to that, depending on the angles you need. i.e. do an experiment first.

    Thanks @djh, I've used the contega PC on the wall junctions (on your advice I think) where it works well, but I don't think it would work terribly well on the timber windows. For one the timber is fairly narrow so there isn't much space to stick it.
  5.  
    Posted By: tonyLinseed oil mastic?

    @tony, yes, that had occurred to me, but I'm not sure of the junction detail between the three, wood/mastic/plaster
  6.  
    Would some kind of stick on bead work?
    •  
      CommentAuthordjh
    • CommentTime7 days ago
     
    Posted By: ComeOnPilgrimI don't think it would work terribly well on the timber windows

    which is why I also mentioned the Tescon Profil!
    • CommentAuthortony
    • CommentTime7 days ago
     
    Mastic on the outside of the frame, lime plaster inside

    Don't let wet lime touch the frame except where invisible

    Do you have cavity walls?
  7.  
    Posted By: tonyMastic on the outside of the frame, lime plaster inside

    Don't let wet lime touch the frame except where invisible

    Do you have cavity walls?

    Hi Tony, why do you say the plaster shouldn't touch the frames? They are sealed with some kind of varnish, so they clean up quite nicely without staining.

    We don't have cavity walls, they are solid all the way through. Why do you ask?
    • CommentAuthortony
    • CommentTime7 days ago
     
    Cavities let in lots of draughts,

    Lime is a paint stripper, stains wood pretty bad, it can and should touch the frame, but keep it from getting on the frame except where it touches, no splashes.

    I would mastic the inside of the frame before plastering
  8.  
    Thanks Tony, that's good advice. I was planning on masticing the edges of the frame.

    In terms of the contact between the frame and the plaster, isn't there a risk that the plaster will shrink back leaving a crack?
  9.  
    Why not use the combination of Profil and Contega tapes (or similar paroducts) suggested by djh, then even if the lime shrinks back slightly you still have an air-tight seal?
    • CommentAuthorKenny_M
    • CommentTime7 days ago
     
    On old houses around here they use burnt sand mastic on the outside between the wooden frame and the stone. I use a lot of linseed oil putty for areas like this that need a flexible, natural type mix that works will with the movement of wood, lime, stone etc. Usually they don't paint over the burnt sand mastic, but I do usually paint over the linseed oil putty. Not sure if this is any help.
  10.  
    Had never heard of burnt mastic until our Listed Building Officer suggested it instead of the Lime Mortar we had put into use. Great material and so simple to use and blends well with our sandstone.
    • CommentAuthorKenny_M
    • CommentTime6 days ago
     
    John - I haven't actually used it yet, there is a company here, masons mortar, who do it in kits of different colours, and I have been meaning to pick up some for the windows in the old part of the house.

    I just used some linseed oil putty on the frames last summer as a temporary repair because I was up there anyway repairing the cast iron gutter with this, and its lasted fine. The linseed oil putty obviously had to be painted for the gutter joints, but I just put it on bare on the window and its been fine so far.
    • CommentAuthortony
    • CommentTime6 days ago
     
    You say, "In terms of the contact between the frame and the plaster, isn't there a risk that the plaster will shrink back leaving a crack?"

    Not a problem if no cavity and window sealed round the frame on all four sides
  11.  
    Kenny

    When you do come to use the burnt mastic I suggest you mix up enough only to be used within 3 days. After that it starts to set in the tub and not as easy to use. I now only mix up half a tub at a time.
    • CommentAuthorKenny_M
    • CommentTime5 days ago
     
    Thanks John, good advice.
  12.  
    I've found some beads that stick onto the window with a groove in them that you can work the plaster into. That way, if there is any shrinkage, it is not noticeable at all. See here: https://www.wemico.com/pvc-window-frameseal-beads

    I ordered the 6mm bead (without mesh) as the reveal is at a slight angle, which will make the angle larger, but it is extremely narrow, so I might order a larger width in the future.
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