Double glazing question

[Penners]

Our conservatory (added to the house by the previous owners) has a failed double-glazing sealed unit, which I am in the process of replacing. I have bought the new DG sealed unit and I'm in the process of taking out the old one.

I've never dealt with DG units before, or with glazing that isn't done with putty. In this case the glazing unit is held in with a wooden beading, which was extremely difficult to remove. I ended up sharpening the edge of a filler knife and sliding under both faces of the wooden beading all the way around the window, then prising the beading off, along with its pins.

The beading was held firmly in place by a brown mastic, as was the DG unit in the rebate in the glazing bar. The drawing below shows where the mastic (in brown) was applied. Either this mastic was applied with incredible skill and accuracy or it's some kind of glazier's mastic "tape". There's no hint of any wandering of its coverage, and it stops exactly at the edge of the beading externally and the glazing rebate internally.

Now (at last!) to my question. Has anyone any experience of doing this kind of glazing? If so, can you tell me what the glazier might have used? If it is a tape, I presume I can buy this from a glass supplier, and it would make life a great deal easier than having to clean up the mess that I know I'll make if I use a mastic gun.

All advice welcome - thanks!

 

[plasticpigeon]

Hello there

I haven't ever replaced a DG unit in a wooden frame but I was going to so have looked into it. DG units are not really supposed to be bedded in solidly frame but should have an air gap round them and drip grooves at the bottom. However if they are to be bedded in using some kind of putty then it must be butyl putty. I have some and it is brown, and can be used very much like normal linseed oil putty. Here is a shop website selling the stuff to give you an example of what I mean.

http://tooltray.com/abrasives,-fixings-%26-hardware/building-products/putty/butyl-glazing-compound-brown-102-2kg.htm

 

[biffvernon]

I use a glazing tape rather than mastic. It's 12mm wide, 3mm thick (squeezes down to about 2mm) closed cell pvc foam and is sticky both sides. Comes in rolls of 25m at about five quid a roll if bought in bulk - might be a good bit more if you buy just one roll from a glass merchant.

You put the tape on the rebate of the frame, then add the dg unit, then another line of tape, then the beading, which I both glue with waterproof Evostick wood glue and nail with brass 25mm pins after pushing down as hard as I can.

Other methods are doubtless available.

 

[JohnB]

I replaced all the windows in my last house with hardwood double glazing (just before all this FENSA stuff). The manufacturers supplied a sticky brown plasticy tape, several mm thick, and longish pins. The idea was to apply the tape to the edge of the glass, and pin the beading in place, but I can't remember the exact details now. It certainly didn't involve using any other adhesive. I managed to crack the biggest glazing unit by fitting it too tightly, but the rest went well!

 

[still_adrianth]

I haven't ever replaced a DG unit in a wooden frame but I was going to so have looked into it.

Likewise. Interesting website http://www.thewindowman.co.uk/misty-wood.htm gives an argument for the need for drainage around the DG unit (shame ours are puttied-in...)

 

[Penners]

I use a glazing tape rather than mastic. It's 12mm wide, 3mm thick (squeezes down to about 2mm) closed cell pvc foam and is sticky both sides. Comes in rolls of 25m at about five quid a roll if bought in bulk - might be a good bit more if you buy just one roll from a glass merchant.

You put the tape on the rebate of the frame, then add the dg unit, then another line of tape, then the beading, which I both glue with waterproof Evostick wood glue and nail with brass 25mm pins after pushing down as hard as I can.

Many thanks for the professional guidance, Biff. I must say that using a tape rather than a mastic is appealing - given my well-proven inability to do a neat and tidy job with putty, I don't imagine I'd be any better with butyl putty.

When you mention waterpoof Evostik, are you talking about their "weatherproof" PVA - the stuff that comes in blue plastic bottles? And don't you find that gluing the beading gives you major problems when the day comes that the glazing needs replacement?

 

[Penners]

I replaced all the windows in my last house with hardwood double glazing

Don't you find that it's rather dark inside your house? :wink:

Many thanks for the information, John.

 

[Penners]

Plasticpigeon and still_adrianth -thanks very much for your responses and the useful links.

 

[88v8]

You put the tape on the rebate of the frame, then add the dg unit, then another line of tape, then the beading, which I both glue with waterproof Evostick wood glue and nail with brass 25mm pins after pushing down as hard as I can.

When you mention waterpoof Evostik, are you talking about their "weatherproof" PVA - the stuff that comes in blue plastic bottles? And don't you find that gluing the beading gives you major problems when the day comes that the glazing needs replacement?

[/quote][/quote]

I wouldn't glue the beading, although if not hardwood it should at least have a coat of varnish all round before fitting. The pins should be solid brass.

Glazing tape is OK provided that the frames are not in winding, it hasn't much compliance. Butyl putty might be a better bet, it fills gaps and is easy to clean off. Available ready-stained. Years ago I was told never to use linseed oil putty with dg units as it attacks the glue holdng the panes together.

Pretty well all the dg units in our conservatory had misted within 10 years, including some large heavy units in the roof. Not pleased, but I dealt with the problem by giving them a severe ignoring. Fortunately, manifestation of the misting needed certain combinations of weather & temperature which didn't arise while the purchaser of our house was there, nor his surveyor...

Here it was, with ivy pruning in progress

 

[AMc]

I'd follow Biff as he knows what he's doing. Our DG windows in the vinery are dry glazed. I thought the tape wasn't adhesive but then I wasn't paying attention when they did the windows as I was still recovering from being the extra pair of hands when we fitted the roof!

A word of warning - the DG seal can be degraded by certain kinds of sealants, putties and fillers. I was told to by the builders get low modulus mastic but when I mentioned I was using it with DG the people at Mr Plastic (Norwich) told me that it would damage the seals. I was supplied LN7 which was a few pence more expensive but the glazing was several £1000. Later conversations with the DG suppliers confirmed this was the right stuff.

http://www.tradefixdirect.com/bond-it-premiere-ln7-silicone-sealant

 

[JohnB]

I replaced all the windows in my last house with hardwood double glazing

Don't you find that it's rather dark inside your house? :wink:

I never understood why I needed the lights on all day after replacing the windows. I wish I'd discovered the reason before I sold the house .

 

[Penners]

Thanks everyone - more useful stuff there.

The business of certain substances attacking the DG sealed unit sealants is a moot one. If you google this problem, just about everyone seems to have a different opinion. I've seen warnings not to use butyl putty and assertions that butyl putty is the correct stuff! Ditto old-fashioned linseed putty and silicone mastic.

What's a poor innocent lad to do? :shock:

Actually, I agree with AMc that Biff should be regarded as the fount of all knowledge on this one.

 

[plasticpigeon]

Hello Penners,

As I try and do up my house, I realise that there are a million ways to do any little job, I just try and gather info and choose the most logical solution. I know that wood and DG units expand and contract with changes in temperature and moisture content. Linseed putty goes hard so these movements can put some stress on the rubber seal on the perimeter of the unit, or at least that makes sense to me. The butyl putty doesn't go hard but stays flexible so should allow a bit of movement and put less stress on the seals when it does move. Perhaps tape is even better as it doesn't touch the seal at all!!!!. However with solid bedding I would want to make sure that there was no chance of water sitting in the rebate between wood and perimeter seal. I'd have more confidence in putty than tape for this but I'm no expert. As an aside by mum had double glazed units put into her bay window by having them bedded in linseed putty like normal window glass. The builder/glazier was none to careful and I can see voids where water can run between the DG unit and the frame. 15 years later they are still fine, no misting at all, but the wood is rotting!!!! I wouldn't recommend this method but it makes me think that quality of manufacture of the units is as important as anything, and that is not something most of us have any control over.

 

[Penners]

Plasticpigeon - I agree with you that linseed putty is probably the least favourite option here. I shall almost certainly go for Biff's recommended tape, with butyl putty as my second choice if, for any reason, the tape looks problematic (which I don't think it will).

 

[biffvernon]

- the stuff that comes in blue plastic bottles? And don't you find that gluing the beading gives you major problems when the day comes that the glazing needs replacement?

Yes and yes, but the idea is that the glazing doesn't need replacing. If it does then the beading gets destroyed as, as it says on bottle, the glue is stronger than the wood. But beading is the cheap bit.

 

[AMc]

The business of certain substances attacking the DG sealed unit sealants is a moot one.

We smashed the last roof unit fitting it and had to order a replacement. This one arrived with metal foil tape around the edges of the DG seal unlike all the others. When I asked the delivery driver about it he casually mentioned that it was to protect the seal from attack by sealing materials and "lots of people" ask for their units like that. Sadly I didn't know it was an option or I would have specified it, it made little or no difference to the overall cost of the replacement unit.

 

[Penners]

the idea is that the glazing doesn't need replacing

You obviously haven't got grandsons who are mad-keen on football!

 

[biffvernon]

I thought it was only 2mm thick cylinder glass that breaks in that way.