Double glazing tip

NeilD · Jul 08, 2007 11:48 pm

I'm in the process of a hallway reno...new entrance door, security door and replacement glass at the side of the door. The original glass at the side of the door was the old seventies type bronze 'bottle glass'. I decided to replace it with a more modern frosted white glass, and whilst doing it decided to double glaze it. When I went to the local glazier to buy the second lot of glass he gave me a little tip. When double glazing a fixed and sealed area, put a couple of those little sachets of silica crystals in the gap between the glass. Apparently because of the temperature difference between inside and outside, condensation can form and cause problems especially with wooden window frames. The silica crystals will absorb any moisture.

ECOECO · Jul 09, 2007 7:09 am

Hi Neil

Sounds like you have made your own double glazing - which you can do.

Modern double glazing consists of 2 glass panels and a spacer bar which are sealed together to prevent air getting in. The spacer bars - which are usually aluminium but can be plastic, contain silica gel which dries the air inside the double glazed unit (DGU). If the seal breaks down or is faulty then the silica gel cannot control the moisture and condensation will form.

The seal is critical so you must make sure you have sealed your glass panels together or no matter what you will eventually get condensation.

An alternative to making your own DGU is to order exactly what you want from your glass supplier - he can supply a DGU to fit your opening (tell him what width you need and where it is going so he can glaze it accordingly). Then when you install it make sure it will not sit in water - so lift it to create a gap at the bottom behind the glazing bead.

If anyone plans to do this - measure the width available for glazing as a DGU needs more width (you probably can't do this in existing aluminium windows as it's unlikely that you have the width available and you would need new glazing beads) and make sure you glazed to AS1288.

Neil, your sidelight needs safety glass (toughened or laminated) to comply.

Andrew

ausdesign · Jul 09, 2007 7:46 am

Andrew, how long does the silica gel work for ?
Does it have a certain lifespan. ?

NeilD · Jul 09, 2007 9:36 am

EcoClassic

Hi Neil

Sounds like you have made your own double glazing - which you can do.

Modern double glazing consists of 2 glass panels and a spacer bar which are sealed together to prevent air getting in. The spacer bars - which are usually aluminium but can be plastic, contain silica gel which dries the air inside the double glazed unit (DGU). If the seal breaks down or is faulty then the silica gel cannot control the moisture and condensation will form.

The seal is critical so you must make sure you have sealed your glass panels together or no matter what you will eventually get condensation.

An alternative to making your own DGU is to order exactly what you want from your glass supplier - he can supply a DGU to fit your opening (tell him what width you need and where it is going so he can glaze it accordingly). Then when you install it make sure it will not sit in water - so lift it to create a gap at the bottom behind the glazing bead.

If anyone plans to do this - measure the width available for glazing as a DGU needs more width (you probably can't do this in existing aluminium windows as it's unlikely that you have the width available and you would need new glazing beads) and make sure you glazed to AS1288.

Neil, your sidelight needs safety glass (toughened or laminated) to comply.

Andrew

Thanks Eco.
Being a bit of a cheapskate, I did it all myself, though I didn't know about the seal with the silica stuff inside it. The rest of it I already worked out. The gl;*** is already installed (toughened and laminated. The rules for that obviously didn't apply when they originally built the house. The original bottle glass was neither toughened or laminated.

Casa2 · Jul 09, 2007 9:59 am

While waiting for an answer from Andrew a few things from me:

1) Have you considered ensuring that the inside panel can be removed every few years if required. This way if the silica gel is used up then you can remove the panel, replace the silica gel and then replace the panel. I would still go for a good seal first since then you'll be less likely to do anything.

2) You don't necessarily need to use silica gel, any desiccant will do. I used to make my own using copper sulphate. This is bright blue when hydrated, but is light blue/white when dried. You dry it by simply putting it in the oven until it's light colour. Blue is probably not a good colour to have behind your glass, but there are many salts that can be used most of which are white (a web search should yield many). Some of this stuff is dirt cheap and you could put 10 mm along the whole bottom surface.

3) Silica gel, and all desiccants, operate on the principle that they absorb water. Once they're hydrated, that's it - the water absorption process is over. So how the lifespan is based on the level of sealing. If it's a perfect seal then the desiccant will last forever (maybe longer).

Great to see an ingenious DIY house component. We should have more of them.

vpande · Jul 09, 2007 9:19 pm

NeilD I am interested to know how you will fix the additional glass to the existing area... is it some kind of a frame or lining around the glass that will fit
over the fixed area? Any photos?
I am quite new to all this.The idea of double glazing is great but way over my budget. I was wondering if one can mount perspex in flyscreen frames and have them against your glass windows sealing all around with the rubber seal just like flyscreens... :roll:

NeilD · Jul 09, 2007 9:48 pm

vpande

NeilD I am interested to know how you will fix the additional glass to the existing area... is it some kind of a frame or lining around the glass that will fit
over the fixed area? Any photos?
I am quite new to all this.The idea of double glazing is great but way over my budget. I was wondering if one can mount perspex in flyscreen frames and have them against your glass windows sealing all around with the rubber seal just like flyscreens... :roll:

It was all a bit basic, nothing complicated. The original glass was in a wooden frame and the glass was set in a rebate on the outside of the frame with ordinary wooden quad holding it in place. I just used some flat 50mm by 15mm timber to make a frame on the inside, fitted the new glass, sealed it, and covered that with quad. Then I just removed the old glass from the outside, replaced it with the new panes, and then replaced the quad. No pics right now, but I will take some.

ECOECO · Jul 09, 2007 11:52 pm

ausdesign

Andrew, how long does the silica gel work for ?
Does it have a certain lifespan. ?

Hi Ausdesign,

Silica Gel (or any dessicant) works only until it has absorbed enough water, which is about it's own volume. So very little water - it cannot last long in a damp atmosphere and will lose its effect in a short time in an unsealed DGU. You can cook it in an oven to revitalise it but impossible if the unit is sealed.

Andrew