Glazing silicone 'not suitable for double glazes units'...?

Dare say someone will correct me if I'm wrong...
The mastic used to seal the units during construction isnt keen on the fumes given off by silicone during curing.
Many years ago I used to use butyl glazing compound...bit like linseed oil putty but havnt done any glazing for a while so this advice may be a bit dated.

 

Glazing silicone is for glazing single panes with timber beading.

Double glazes units are to be sealed with the correct gasket and plastic beading.

 

your glazing supplier is wrong, wrong, wrong. Although not very common, normal silicone can react with the seals on the sealed unit and break it down.
You should use a low modulus neutral cure silicone.

 

Don't use silicone. I make and fit wooden windows, both single and double-glazed, and for the past eight years I've used the ACRYLIC transluscent sealant readily available from B&Q. Don't know why Screwfix don't sell the stuff. It's overpaintable, goes on white and dries clear. I've NEVER had a call back.

 

So is butyl a thing of the past???

 

It isn't labelled as acrylic and it doesn't appear on their website anyway, but that's not surprising for B&Q. I have to go into B&Q this morning and intended picking up some more sealant, so (if they still sell it) I'll post the details.

 

B&Q's stuff is their own brand and it's simply labelled "All Purpose Sealant". Water resistant, paintable, flexible, for use indoors and outdoors. Transluscent. It's in an orangey tube and costs £3.98. I've just bought ten tubes of the stuff!

 

i think wm meant using silicone as an actual edge sealant between the two panes, well it will work as long as the dessicant can absorb the vapour given off by the curing silicone which is about 4 weeks. as for fitting sealed units with high modulos silicon? nought wrong with it except for decorating purposes in timber frames.

 

slapiton, no he didn't.

The tape I've used has sealed it excellent. It's water proof. I just wanted to run a bead of silicone on the outside to stop water 'sitting' on top of the tape.

BB

 

right i didn't see the second post, anyway silicone does cause problems with decorating but it does keep the water out and any idiot can slap it on.

 

You can almost forget the 'Not suitable for double glazed units' lingo.

Firstly, only a low modulus, high movement, semi-hardening silicone <u>could</u> damage the unit sealing.

That's because the active agent is keeping the silicone from hardening, and may also soften the unit's own sealing.

Once dry a high modulus, fully hardening silicone will be fine.

Not only that, but you should find that MOST DG units have a silver foil(or tape) covering round the outsides, thus preventing contact between these sealants.

To fill your gaps, use whatever you need(whether over paintable, or seal after painting with non-paintable).



Mr. HandyAndy - Really

 

There you go. The sealant you use is never going to be in contact with the unit sealing.

High modulus generally means it sets harder and doesn't allow as much movement.
Low modulus generally means higher flexibility and some 'cures' mean some sealant actually stay 'tacky throughout their life. Each manufacturer seems to have a different idea as to what their level of cure is, and some silicones with the same spec may act differently than a competitors.

I think most contractors generally try out a few, until they find the one they can rely on, then stick with it.

Dow Corning do a good range and many swear by them.

Mr. HandyAndy - Really

 

don,t worry about it andy,your plastic windows have rubber gaskets to keep the water out. but right enough what is going to last longer the rubber or the plastic? even the dodgy sealed units might outlast both.

 

Hi billhicks,

Most low modulus sealants are not suitable for bedding in sealed units. It says on the product spec sheets "do not allow it to come in to contact with the butyl layer" or something like that. The vast majority of them will leach in to the butyl layer over a few years and break the unit down. Hybrid polymers will do the same and have the same message on the spec sheets, or will not mention it at all. The products that are suitable are Hodgeson U9, Everbuild 450, Soudal Silirub 2 and DL chemicals Parasilico Pro Glass. There may be more but these are the 4 I know are designed for this job.

 

David Robertson is correct, not all low modulus silicone is suitable to bed in double glazed units. He has also named the best silicones to use, there is another one called Timbaglaze but I haven't tried it. I actually phoned Soudal about their product ( Silirub 2) and they are very confident in their product.