How to install double glazing

[Zebra]

I've had new timber windows made for my house, and after the glazers had been to fit the new double glazed units, I was horrified. The outside looked fine but the inside was a dog's dinner. The beadings weren't square, the corners were bashed to try to make them go square, the nail heads were sticking out, and the beadings were all split. I paid the glazing company for the glass but not for the fitting, and told him forget it, I can do a better job myself. The joiner has given me some new beading for free.
The two windows which are done, it's mostly just a question of redoing the beading, but there are another two windows on the way.
So, how do you fit double glazing?
It seems that there is a bead of putty on the outside (I understand that this ought to be butyl putty?) and it seems that the panes are sitting in a solid bed of silicone (I understand that this ought to be neutral cure silicone?) with some tiny spacers inbetween the pane and the rebate. Where do you get these materials? Can't find them in any normal builders merchants. How specifically do you apply the putty and the silicone, how much do you use?
I realise this isn't specifically a question about period properties, but I'll bet there's one of you out there who knows!

 

[plasticpigeon]

I'm sorry that they weren't fitted well. Thankfully it seems that the damage is easily corrected. There are window experts on here for sure. However I know that butyl putty is not supposed to be used to form a bead infront of the glass but just for bedding in or to be used behind a wooden bead. However many say dg units shouldn't be bedded in solidly and should have an air gap round the edge with drip grooves and drainage underneath.

 

[worms]

Do I take it from your description that the rebate is to the inside of the window and the units are inserted from inside and the beading then added to the inside surface? Not that it necessarily makes any difference, I guess, to the process!

I've been trying to read up on all this for the imminent* diy retrofitting of dg units into my casements. I had been working on the assumptioin that i would use glazing tape to bed and hold the units in place, rather than a putty or silicon sealant. Happy to get more advice from any of the experts, though!

*Its been imminent for a couple of years now, I am still on the Kit-Kat phase but getting closer!

 

[worms]

However many say dg units shouldn't be bedded in solidly and should have an air gap round the edge with drip grooves and drainage underneath.

I've been advised to allow 3mm all round.

 

[eezageeza]

neutral cure silicone?

If your local builders merchant doesn't have this, you'll find it in the Screwfix or Toolstation catalogues - usually described as "low modulus neutral cure" I seem to remember.

I think you can use pretty much anything to space the unit off the frame while bedding it in - we used little bits of plastic, cut to size.

 

[88v8]

Spacers of varying thicknesses, jolly useful,
http://www.amazon.co.uk/Window-Glazing-plastic-packers-spacers/dp/B004REXJDU

To prevent the glazing bead from splitting, especially if hardwood, pre-drill the nail holes. Sorry if this is statin the bleedin obvious...

When we had our teak conservatory built in 1990, the joinery was superb but the on-site fitting quite awful. They just wanted to get it in place any old how, so they could collect the stage payment. I sent them away after a while, and ended up redoing a lot of it, including plugging and redrilling most of the door & window hinges. No shortage of bodgers in the building trade.

Ivor

 

[AMc]

From memory we used plastic spacers and dry glazing tape. No silicone was used on our regular windows. Your glazing supplier will have the spacers and tape you need. My experience was they were happy to supply it for a price when asked but were also happy to send £1000's of units without it if I didn't.
If they don't then ring the next glazing company in the book.

When we needed sealant for the glass roof I was told that "LN7 sealant" is the right stuff. I had gone to buy "any old low modulus sealant" from the plastics specialist (Mr Plastic, Norwich) and was told that many builders use the wrong stuff and that leads to the seals failing prematurely. When I quizzed the builders why they'd suggested a cheaper alternative they'd told me they were just trying to save me a few quid (on my expensive glazing?) and the LN7 was the best sealant they'd used - then using it everywhere :lol:

If you are doing the glazing yourself then I would recommend borrowing or buying at least one glass lifter - it makes handling much easier. The plastic ones from Screwfix for £7 are more than adequate for a few jobs. Make sure the plane is dust and grease free and keep the suction cups very clean of dust and grit so you get a good seal on the glass and don't scratch the rubber.

 

[worms]

If you are doing the glazing yourself then I would recommend borrowing or buying at least one glass lifter - it makes handling much easier. The plastic ones from Screwfix for £7 are more than adequate for a few jobs. Make sure the plane is dust and grease free and keep the suction cups very clean of dust and grit so you get a good seal on the glass and don't scratch the rubber.

Yes, picked up one of these last week for replacing some glass in a couple of single-glazed windows, certainly well worth the money and makes the whole thing so much easier.

 

[Zebra]

However many say dg units shouldn't be bedded in solidly and should have an air gap round the edge with drip grooves and drainage underneath.

Yes I've heard that too but my frames weren't designed that way, so I have to go the "solid bed" method.

Do I take it from your description that the rebate is to the inside of the window and the units are inserted from inside and the beading then added to the inside surface?

Yes that's how mine have been designed.

If your local builders merchant doesn't have this, you'll find it in the Screwfix or Toolstation catalogues - usually described as "low modulus neutral cure" I seem to remember.
I think you can use pretty much anything to space the unit off the frame while bedding it in - we used little bits of plastic, cut to size.

That's the thing, Screwfix don't seem to have any low modulus neutral cure silicone. Thanks for the tip re the spacers.

Spacers of varying thicknesses, jolly useful,
http://www.amazon.co.uk/Window-Glazing-plastic-packers-spacers/dp/B004REXJDU
To prevent the glazing bead from splitting, especially if hardwood, pre-drill the nail holes. Sorry if this is statin the bleedin obvious...

Those spacers seem way too big. My glass has been made quite tight for the frames. The spacers the fitters have used are soft, like neoprene, about a centimetre square and about a millimetre thick.
Yes, I am planning to pre-drill the beading, when I've made a complete new set!

When we needed sealant for the glass roof I was told that "LN7 sealant" is the right stuff.

That's funny, that seems to be sold as a tile sealant, and not for glazing. I was thinking of getting this stuff http://www.wholesaleglasscompany.co.uk/acatalog/Silfix-U9-Glazing-Sealant.html.

 

[AMc]

First google hit on LN7 sealant
http://www.platinumchemicals.co.uk/ln7-lmn-builders-silicone-p-293.html

Product Uses
LN7 LMN Silicone can be used in construction, engineering and electrical applications. It is used as a high extensibility sealant for external and internal applications, including expansion joints, and perimeters of frames, as a rubber adhesive for bonding most materials, as a potting compound to encapsulate electronic components to protect from moisture, tampering and shock, as a gasketing material and as a bedding compound for glazing double glazed units into timber frames.

LN7 LMN Silicone is inherently resistant to fungal attack. Accelerated aging tests indicate a life expectancy of in excess of thirty years.

And from the manufacturer...
http://www.bond-it.co.uk/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=281&category_id=88&option=com_virtuemart&Itemid=3&vmcchk=1&Itemid=3

Compatible with all metals and plastics and contains no components that can degrade insulating glass seals.

I'm sure there are other suitable products inc. the one you linked.

 

[Zebra]

Oh, that's really helpful. Thanks, didn't find that. Sounds like that's the stuff then.

 

[agbagb]

The good news is that it possible to sucessfully fully bed DG in timber frames. The bad news it's not easy to do reliably.

The tricks are to cater for all the differential movement to ensure that the silicon doesn't pull away from the glass or the timber. Even with low modulus silcon (and yes it has to neutral cure) it will need pressure on the seal to work reliably.

I would do it in two stages.
First fit the DG unit in the frame and pack it in place with anything (you'll be taking them out later). Make sure there's 2-3mm from the front of the rebate. Then gun in silicon between the glass and rebate all the way round from outside making sure it squidges around the outer pane of glass, have go from the inside if you need to. Wait for it cure and take out the packing.

Next completly fill the remaining gap.inc. the holes from the packing and fit the beading (the bead should have some silicon on the back of it). But fit it really tight so it applies pressure to the cured silicon. It might be easier to do with No.4 screws instead of with pins. It may also be easier to have scribed joints instead of mitres on the beading corners.

The result will be a fully bedded unit with a seal at front that will/should stay good as the wood and the glazing unit moves. The butyl seal of DG should be protected from external moisture and moisture from the timber. Condesation on the inside shouldn't get past the beads.

 

[worms]

agbagb, that's a useful description of the technique, thanks!

Any experience/comments on the glazing tape approach?

 

[eezageeza]

I've bedded dozens of DG units (we've replaced 22 windows by now, all georgian style, so dozens and dozens of little units). Mostly 10-12 years ago. The first couple of dozen units we used tape, thereafter we used silicone. Today, most of the taped units have blown, but none of the siliconed ones have - so my recommendation would be don't use tape!

My technique differed slightly from agbagb's - I ran a bead of silicone around the frame, then bedded the unit onto that (with spacers underneath to hold the unit off the frame) then siliconed all around the unit, very generously, including over the spacers (which were cunningly sized to fit right under the dg unit) then fitted the beading. Silicone should squish out of all orifices (inside and outside). Once it's cured, remove it with a sharp blade.

 

[agbagb]

Any experience/comments on the glazing tape approach?

I bought some tape to experiment with. Its not very compressable so won't accomodate much movement. The rebate would need to perfectly flat and smooth, it s probably perfect for plastic windows.
Timber will always expand and contract (aluminium glazing spacers will also expand, foam type "warm edge" spacers are better) whatever is used to make the seal will need to expand to fill any opening up of the filled gaps. So that's why I recomend letting the silicon cure on the outside seal then compressing it with the beading. Silicon would stretch if well stuck on both the timber and the glass in reallity it would pull away. If its pre-compressed the seal should hold.

eezageeza (and for anyone with fully bedded units), It might be worth checking that the seal to the timber is holding so no moisture is getting in that could eventually rot the timber even if the glazing is ok.