Fitting double glazed units to timber doors?

[flanajb]

This is an area I have never really been sure about. When fitting double glazed units to timber doors and the bead is on the outside face of the door, do you use a timber bead or should I use glazing putty?

If I can use a timber bead how do I ensure I get a good seal between the glass and the back edge of the timber bead so that water ingress does not occur between the bead and the glazed unit?

Sorry for all the questions.


Thanks

 

[deema]

I would firstly use glazing foam to 'stick' the glass into the rebate. It's a thin double sided sticky foam about 10mm wide. This ensures that the glass has somewhere to go when the door 'breaths'. I would then use glazing silicon sealant to bed the bead against the glass. A few pins keep sere thing then in place. Some people place a small shim between the glass and the beading, tack it into position remove shim, and then fill the gap with sealant. The practice does not in my opinion look as good as pushing the bead hard up against the glass if the door is to be left natural either varnished or oiled. Looks fine though if it's going to be painted. The reason for doing this is that it makes any subsequent removal of the glazing a doodle. A Stanley knife can easily be run around the bead in the very small gap.

 

[flanajb]

I would firstly use glazing foam to 'stick' the glass into the rebate. It's a thin double sided sticky foam about 10mm wide. This ensures that the glass has somewhere to go when the door 'breaths'. I would then use glazing silicon sealant to bed the bead against the glass. A few pins keep sere thing then in place. Some people place a small shim between the glass and the beading, tack it into position remove shim, and then fill the gap with sealant. The practice does not in my opinion look as good as pushing the bead hard up against the glass if the door is to be left natural either varnished or oiled. Looks fine though if it's going to be painted. The reason for doing this is that it makes any subsequent removal of the glazing a doodle. A Stanley knife can easily be run around the bead in the very small gap.

Thanks. I did use glazing silicon to bed the bead against the glass, but I think the seal must have gone as water is getting in between the bead as I am getting water ingress on the inside of the doors. If you do use glazing silicon how does this work when painting the doors as the paint will not bond to the silicon bead and in my experience the 2 mm paint overlap on the glass also helped seal the unit and the beading?

 

[MMUK]

When you measure the unit up, allow a 5mm gap along the bottom edge and sit the unit on packers. This will help prevent the unit sitting in water and breaking down the seal. I also put two half round's into the bottom edge of the bottom bead to allow any water to run out. HTH

 

[deema]

+1 for using packers.

The glazing silicon comes in black, brown and white normally. You can use any good high grade silicon where there is a wider choice of colours. The silicon as you rightly point out does not take paint and makes painting the sashes easier. I wouldn't paint the window, you don't want anything that stops the wood moving independently to the glass. It's the relative strain on the outside glass sheet compared to the inside glass sheet that breaks down the seal. You want the glass to 'float' within the fixings. Hence don't use standard putty as this goes hard, double glazing putty in time also goes rock hard. When this occurs the double glazing will fail very quickly.

 

[MMUK]

Don't forget clear silicone, deema

 

[Berncarpenter]

When fitting DG units i allways take the glazing tape off the unit before its fitted as this can come away from the glass and cause problems with units leaking and breaking down. Also pack the unit up and dont seal the gap so its not sitting in water .

Cheers Bern

 

[blackrodd]

I keep the rebate on the inside, and, as Bern said, take off the glazing tape and using glazing mastic, put a decent mastic bed all round the rebate, and sit the DGU on a couple of packers, push into the bed, leaving about 2 mm thick bed, tack in some sprigs to help support the glass.
Fit beading or quadrant to the inside rebate after a couple of hours
The excess mastic is cut off and carefully removed when set the next day, with little mess.
This keeps the mastic off the woodwork and causing problems with painting and the unit is sealed in nicely and weather proof. Regards Rodders

 

[RogerS]

...This will help prevent the unit sitting in water and breaking down the seal. .....

Is that statement correct? I can understand that if the seal develops a small hole then as the air inside expands/contracts with heat or sunlight falling on the unit and the unit is sitting in a pool of water then the water will get sucked up inside the unit as the air inside the unit cools.

But water actually making a seal fail?

flanajb....that's why I 'reverse' my windows in that I put the rebate on the inside of the window and have a spindle moulder cutter that cuts what looks like a bead of glazing putty on the external face. My beads then get applied on the inside face. Reason was that I found that applying small beads of wood on the outside face (even siliconed in) in lieu of putty would inevitably bend and warp and pull away from the glass letting water in.

 

[Steve Maskery]

There used to be an excellent (and at the time, free) article by someone called Hislop about the design of DG windows, discussing practice from all round the world, especially USA, Germany and Scandinavia, where they regularly have much more severe weather than we have traditionally had here.
When I did my windows in my last house, I followed his best practice advice, which I'll try to précis.

There should be a 3mm air gap around all 4 edges. This air gap should be vented rather than sealed.
This is achieved by sitting the unit on two or three packers, which are the full depth of the rebate, so they end up flush with the outside face. This is important.
The rebate is painted before the glass is installed, then a generous squirt of glazing sealant applied to the rebate. The DG unit is pressed hard into the silicone so that there is squeeze-out. Painted beading then has a generous bead of silicone applied and is pressed into place along the top and both sides, so that again, there is squeeze-out. This is to prevent water getting in between the beading and the glass, causing damage and looking unsightly from the inside.
Finally the bottom bead is applied. This is L-shaped with the short arm of the L acting as a drip strip over the bottom edge. It is pinned into place through the packers, so that there is an air gap underneath it. The result is a unit that can move but is sealed from water, but can drain (under that lower bead) and is ventilated so that water does not accumulate either by rain or condensation.

The silicone sealant is trimmed flush when cured.

I wasn't in the house long enough to tell you what the lifespan was like, but when I told the glazing supplier how I was doing it he commented that it was a Rolls-Royce job and if he were doing his own house, that is how he would do it.

If you can find it online, the Hislop paper is a good read.

HTH
S

 

[MMUK]

...This will help prevent the unit sitting in water and breaking down the seal. .....

Is that statement correct? I can understand that if the seal develops a small hole then as the air inside expands/contracts with heat or sunlight falling on the unit and the unit is sitting in a pool of water then the water will get sucked up inside the unit as the air inside the unit cools.

But water actually making a seal fail?

Hot melt sealant is not designed for continuous immersion and this does lead to failure of the seal.

What's more important is to make sure that the unit sits completely on the packers. I've changed some failed units only last week in a conservatory where the packers had only covered the outer pane and the spacer. The internal pane had slid down by about 5mm which broke the seal.

 

[axe]

Finally the bottom bead is applied. This is L-shaped with the short arm of the L acting as a drip strip over the bottom edge. It is pinned into place through the packers, so that there is an air gap underneath it. The result is a unit that can move but is sealed from water, but can drain (under that lower bead) and is ventilated so that water does not accumulate either by rain or condensation.

The silicone sealant is trimmed flush when cured.

I wasn't in the house long enough to tell you what the lifespan was like, but when I told the glazing supplier how I was doing it he commented that it was a Rolls-Royce job and if he were doing his own house, that is how he would do it.

If you can find it online, the Hislop paper is a good read.

HTH
S

I did mine exactly like this except that I put the bottom bead in first and bedded the units on butyl.

They have been done for nine years now and not one issue with them.

Previous to this I fitted some units into some existing sashes without venting the bottom bead and the units lasted all of two years.....

My view is that however well you seal the beads, over time water will get past and sit in the bottom rebate because it has nowhere to go and it seams to me that would send the bottom rails rotten too.

just an opinion though................

 

[Steve Maskery]

Actually, come to think of it, it may have been butyl rather than glazing silicone. Does in come in tubes like mastic or in a tub like putty? This was definitely in a tube for a gun.

 

[axe]

I've only ever seen it in a tub but I do recall seeing normal putty in tubes so maybe someone does it in tubes.

Nice thing about using it from a tub is there is no waste as any squeeze out you cut off and it can go back in the tub for re-use.

Cheap too............but I am tight

Dave