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    • CommentAuthorpmagowan
    • CommentTimeFeb 4th 2012
     
    Hi all, me again!

    Some of you will remember that my plan for windows is a 28mm 3G Krypton filled unit (Ug 0.6-0.7) fitted in a modified sash frame set out into the EWI layer. In this scenario the main problem is the frame. I will have to create a large rebate to fit the units which would require clever use of a router and some skill. I have thought of another way and wonder what you guys think.
    Basically I will split the frames (along the plane of the glass) and insert a 10mm insulating board of some type into the middle before sticking them back together with glue. This will make the frames deeper and thus make the rebate problem easier (no router required). It will also give a thermal break.

    What material would you use as a thermal break and how would you stick them together?
    • CommentAuthorJoiner
    • CommentTimeFeb 4th 2012 edited
     
    Within (structurally rigid) reason I don't think a laminated thermal-break section of 10mm thickness would compromise the frame at all, not least because the window will be supported across its width and depth within the reveal anyway. Any dense insulating material would suffice (?).

    Back in the 80's I works managed a factory that helped develop the first mass-production of a combination upvc-aluminium window called 'Harmony', a system developed and manufactured by MDC (since defunct, I believe). The two materials were bonded and then a channel in the ali frame section filled with a foam material (can't remember it's name) that formed a rigid thermal-break. The closed side of that channel was then routed out to make the thermal break. They were very strong windows.

    So the idea is sound.

    If I was thinking of doing what you suggest I'd do some test-pieces first and the first thing I'd try would be contact adhesive, the three sections fastened together with the fixings illustrated in one of VH's recent pictures, showing roof insulation in place with screws passing through a plastic tube-like sleeve, the flange of which stopped it pulling through the insulation material.

    (You've actually given me an idea for further development work on drawings for a 'ventilated glass' window. Excellent.)
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 4th 2012
     
    Oo I dunno - 44thk sashes sawn down to prob 21thk? Won't that leave the tenons with little lateral dimension to prevent twisting apart? If you cd hold the jelly in shape I suppose it wd be re-stiffened once re-glued. For all that, surely brand new sliding sashes?

    Bodging it, you'd still have v inadequate rebate 'floor' width - 16mm reqd, not 7mm as in a typical 1G sash. I've posted drawings on here of how to do new, authentic sashes for 2G, adaptable to 3G pref using HeatMirror middle pane, tht will fit extg. box frames.
    • CommentAuthorpmagowan
    • CommentTimeFeb 4th 2012
     
    Glad to be of help:smile:

    Thanks, it's good to know it is or can be structurally sound. They will be fixed frames (non opening). The problem now is which glue and which insulation. Obviously the insulation needs to be thermally efficient as well as structurally competent.

    The other thing is should I look at different glazing? Thickness will now be less of an issue. Is Ug 0.6 good enough? 28 mm units are better looking but maybe a 32mm unit would be better thermally.

    Thanks again
    Paddy
    • CommentAuthorpmagowan
    • CommentTimeFeb 4th 2012
     
    Fostertom, once cut I calculate 23 mm each. The outside half plus the insulation would give at least 33mm rebate for a 28mm unit. Giving 5mm for putty. Obviously I could increase the insulation thickness if more rebate is required. As for the tenon strength, remember these are non-opening units and therefore will be permanently fixed to the box which will resist any twisting etc.
    • CommentAuthorJoiner
    • CommentTimeFeb 4th 2012
     
    Tom, you can fix the corners by using mitred corners and slim slip-tenons (or even biscuits) and a belts-and-braces bracket at the corners on the wooden edges because they'll be going into the boxed reveals.

    VH, or anyone - where do you get those insulation fixings from? (Hope my verbal description is good enough to identify them.)
    •  
      CommentAuthorjonharris
    • CommentTimeFeb 4th 2012
     
    When I did my sash windows I cut off the rebates flush then pinned and glued new beading on both sides. Frames only 40mm thick but allowed for 20mm (4-12-4) double glazing with a 8mm bead and 2mm glazing strip. With units firmly siliconed in round the edges, the glass is already secure, so a thin beading is ok. With 44mm frames you could get in 4-16-4 using this method.
    • CommentAuthorpmagowan
    • CommentTimeFeb 4th 2012
     
    That's certainly an option Jon. A problem is that there is moulding on the frame on the inside but I could get round that by using moulded beading. The frames would still need taken apart and it woul not improve the insulation. With 28mm units in a 47mm frame that gives 9mm for beading either side and 1mm for silicone. I am tending towards the split frames as I think that I may be able to improve my Uw. The problem is how to do it!
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 4th 2012
     
    Posted By: pmagowan5mm for putty
    That's early death to a 2G/3G unit. Putty is out of the question, even mastic bedding is asking for trouble. The whole hidden edge (front back and edge) must be dry, ventilated and free to expand/contract. That means dry glazing tapes front and back, well compressed by the glazing bead. The tapes are 12mm wide and there must be 3mm free space around the edge of the 2G/3G unit, so the rebate floor or 'platform' the unit is compressed against must be 16mm wide. Nothing less will do.
    • CommentAuthorpmagowan
    • CommentTimeFeb 4th 2012
     
    Well that points even more towards splitting the frame for depth if I understand you correctly. Are you saying the rebate depth should be 3G thickness plus thickness of 2 compressed pieces of glazing tape plus bead? And that it should be high enough to take the tape plus a few mm. I have to admit that I don't understand glazing in anything above SG where I use traditional linseed oil putty.
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    Tom, you're continuing to push the taped-fixed glazing by rubbishing the use of sealant. I have 18 years of extant d/glazed work (windows and doors) that says you're talking cobblers.

    How many times have we had this argument? Yet despite all the testimony to the contrary you still insist that the taped-and-drain method is the only one for a wooden window. WRONG!

    I HAVE NEVER HAD A UNIT FAIL EXCEPT FROM A MANUFACTURING FAULT.

    Very recently I challenged the "drain" school to explain how they'd a) make the water run downhill within the casement/sash and then b) make its way out through drainage hole(s).

    There is no need if water is prevented from getting in in the first place, and that is EASY to do with modern ACRYLIC sealants which, if transluscent, dry clear and are overpaintable.

    The secret is in the application. A run of sealant along the edge of the rebate onto which the unit is pressed. With the unit bedded onto the sealant, run sealant along the outer edge-line of the spacer bar, and along the top edge of the rebate, the glazing bead is then pressed into place onto these two runs of sealant, with sealant applied to the ends of the glazing bead to seal the corners. Leave the first run of bedding sealant to cure before trimming back with a glazing knife (in other words, don't turn the casement/sash over yet or it'll drop out). The sealant pressed out by the bead can be skimmed off the glass with a glazing knife and the excess along the top edge of the bead also skimmed off and smoothed flush with a finger to create a nice smooth profile that looks good when painted. Store them on top of each other until the sealant is cured (overnight is usually enough) and then trim off that first bedding run of sealant.

    Like I said, 18 years without a failure tends to make you wonder, don't it?

    And, incidentally, as mentioned in another thread somewhere, I've been called in to replace a LOT of glazing fixed with the glazing tape method.

    Each to his own. But stop rubbishing mine. :devil::wink:
  1.  
    Joiner

    I am looking to put triple glaze units direct into stone mullion frames is there any sealant you would recommend for this . I was going to use standard insulation foam to allow the window to expand.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012 edited
     
    Sorry Joiner - I honestly don't remember prev correspondence about this, so maybe I shd revise my ideas. Thanks for the detailed instructions.

    Do we agree on the 16mm rebate platform? How much clearance nec around outside of 2G/3G unit, inside the woodwork? What's minimum depth (in to out) reqd for the glazing bead? Bead how fixed - pin or screw? What to allow for nom thickness of the 2 mastic beds, inside and outside? In other words, how much deeper than the 2G/3G unit must the rebate be?

    With mastic bedding, plus glaze-in detail (glazing bead to the inside), is there then no need for an aluminium drained bottom bead - cd the rebate upstand be run across the bottom rail, trusting there's nothing that wd need be drained out?
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    Sorry John. No experience of doing that onto stone. The only (and it's a stretch) similar situation was single glazing into old oak mullions which was bedded-in on transluscent acrylic sealant and then puttied. 3g straight into stone mullions? The face onto the rebate isn't a problem with the bedding bead of sealant (and the unit sitting on packers to even it up), whichever way it's glazed (internally or externally), it's making it look "right" on what would otherwise be the glazing-bead side.

    What I could have made clear in my rant to Tom (sorry mate) was that the way I do it avoids the interaction predicted between the sealant and the hot-melt more by accident than design, because that's the way I've always done it in ignorance of the science that says it's critical to avoid it. Back to the old "He didn't know it was impossible" scenario. The method I use (and which others who've now taken to using the method have adopted) had more to do with getting away with using as little as possible rather than avoiding contact with the unit's edges - although my method still advocates the use of "copious amounts", the squeezed excess guaranteeing a good waterproofing seal, which is the whole point.

    Having said all that, in the early days I DID apply the sealant all round the unit and only stopped because I wondered if there was a less expensive way of achieving the same end than just throwing gallons of sealant at it, and those windows are amongst the ones still going strong.

    Is there absolutely no way of getting even a minimal frame of sorts around those units, John? I'm always reluctant to trust the tape edges that units usually come with because I've seen systems fail by moisture weakening the tape edges, enough to allow water to find its way around and under the tape to the inside of the unit, but that was on a conservatory roof and it took ages to realise what was happening! Since when I always stipulate "no tape" on every unit I order.

    So I'm out of ideas based on first- or even second-hand experience.

    Sorry John.
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    Tom, will have to come back on the detailed questions. Need to clear out all this morning's 'incoming' first. :bigsmile:
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012 edited
     
    So in yr further comments Joiner, am I right that you do in fact leave fresh air around the perimeter of the 2G/3G unit? If so, then I'm happy.

    renewablejohn, are your stone mullions glaze-in or glaze-out? In other words, did the original putty splay face inward or outward? this is a situation I'll prob be facing myself shortly - I'm hoping they're glaze-in, but fear they're glaze-out, which is def more tricky.

    One time, in 1G days, I fitted a thin 'frame' of aluminium odd-leg angle, made up welded at the corners, tight into the rebate of somewhat wavy/decayed Bath stone mullions, to provide a flat (and slightly widened - visibly, but didn't seem to matter) rebate 'floor' to direct-glaze fixed glass to, and also to tap and thread into for hinges for some timber opening lights incl draught strip against the flat Al face. This was glaze-out. Worked v well.
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    Yup, the "fresh air" is the space created by the glazing tolerance of 2mm all-round, and packers on the bottom edge to maintain the position of the unit within the casement/sash frame, but I'd hesitate to call it "fresh air" in air-circulation terms because that space is sealed, and certainly not to allow drainage, a la upvc windows.

    On the stone mullion glazing... Of course, it's usual in this situation for the glazing to be in edging of some kind, often lead cames. Which makes me wonder about retaining that "traditional" method by edging the 3g units with lead (flashing) and sealing along the edge of that with sealant prior to puttying because, drying clear, it'll be virtually invisible. In fact that's probably the way I'd go if I was doing the job.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012
     
    You'd actually form a lead U-channel (like a came) to hold the 2G/3G unit, and mastic the lead to the surround?
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012 edited
     
    I can't think of any better way, it's just an "enlarged" version of the s/g traditional method and could, with care, be dressed around the unit.
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012 edited
     
    And this is how one of the sashes here looks (before touching up)...

    [IMG]http://i41.tinypic.com/351fv3n.jpg[/IMG]

    You'll notice the duplex bar! Haven't caved in, it's just that this window fronts the building and needs to match very closely with the upstairs window directly above it because it's "on show" from the lane.

    Taking each of the elements of your query above...

    "Do we agree on the 16mm rebate platform?" -- To suit the sightlines.

    "How much clearance nec around outside of 2G/3G unit, inside the woodwork?" -- Normal (for me) 2mm glazing tolerance, with a strictly insisted upon absence of parallelism on the panes, failure to comply and units returned.

    "What's minimum depth (in to out) reqd for the glazing bead?" -- 12mm for me. Bead cut to, say, 14mm (easier to handle), moulding applied, bead put through thicknesser to reduce to 12mm.

    "Bead how fixed - pin or screw?" -- Neither. Cut to good snug fit and pressed into sealant which holds it in place.

    "What to allow for nom thickness of the 2 mastic beds, inside and outside? In other words, how much deeper than the 2G/3G unit must the rebate be?" -- 2mm is fine. On the current windows with 16mm d/g/ gas-filled units, then 16 + 14 = 30, bead reduced to 12mm gives a slightly recessed finish which, with the sealant smoothed along it with a finger gives a good finish when overpainted.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012 edited
     
    Posted By: Joiner"Do we agree on the 16mm rebate platform?" -- To suit the sightlines.
    Don't understand that - must be important, the width of the flat face against which the 2G/3G unit is pressed, on mastic bead?

    Fine looking sash. We just got round to installing the stick-on inside and outside (duplex you call it) 'fake' glazing bars to 4-12-4-12-4 units. As usual you can readily see, if you go looking, that they don't go right thro but I say 'so what' - the effect is transformative for the better.

    Before:
      2009-03-28 007.jpg
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012 edited
     
    After EWI and new 3G Russell windows:
      2011-04-19 160med.jpg
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012 edited
     
    With bars, incl to an02ew's new Phase 2 extension:
      2012-02-05 101.jpg
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    Sightline can vary according to how "out of sight" you (though usually customer/planner/CO) want the spacer bar to be. Some people don't mind having them in sight, something which drives me nuts. A lot has to do with the colour of the spacer bar. In that sash of mine, although not obvious in the pic, the spacers are white and so can sit quite close to the sightline.

    Gave the example yonks ago, about my son intending to fit d/g into his Listed house neighbouring the Nene Valley Railway yard (old railway worker's cottages), when the CO said she didn't mind double-glazing so long as she "couldn't see the foil", the 'platform' (new expression to me, but I gathered what you meant) was 18mm, whereas my standard is 15mm.

    The duplex bars on my sashes are mitred into the top and bottom beads.
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    The houses at the back look interesting. Is that the "development in the valley" you've been working on for so long?
    • CommentAuthorpmagowan
    • CommentTimeFeb 5th 2012
     
    So to get the glass i need to measure the opening for the glass and add 15mm on each side for hight of rebate minus a couple of mm for clearance? If i want the spacer to disappear i can add more.
    • CommentAuthortony
    • CommentTimeFeb 5th 2012
     
    I have used narrow spacer bars and only 1.5mm clearance!
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012 edited
     
    Even more food for thought - so what's really the minimum width for rebate platform, incl 2mm clearance beyond the glass unit edge, if you don't mind the spacer showing?

    As tony says, we can start considering narrower spacer bars - but isn't there doubt as to their durability? They shd be better thermally.
    • CommentAuthorpmagowan
    • CommentTimeFeb 5th 2012
     
    The other question I have is; If i split the frame then technically there is no limit to the thickness of my 3g. The only reason I was using 28mm 3g was that it fits a narrow frame and may look a bit better. Should I be considering a 32mm glass unit? Is Ug0.6 good enough? Would a thicker unit with less exotic gas be a better U for £ ratio?

    So many questions!:cry:
  2.  
    Great idea with the lead flashing. My windows are only 12 inches wide and the plonker of a conservation officer insists that we replace softwood with oak frames with all bars being the width of the opening windows so 2 inches lost on either side so now only 8 inches of glass. I have one original leaded window lime mortared into a stone mullion so the precedent is set. Unfortunately I have 82 windows to replace 22 in just one room so oak frames are totally out of it. Getting back to the lead flashing would that create a heat bridge around the edge of the glazing unit or am I getting paranoid considering the amount of heat were already losing using single glaze.
   
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