Repairing sealed unit double glazing

[Ken]

Any suggestions for overcoming misted sealed units, is it possible to drill hole and allow it to dry out?

thanks

Ken

[Ian Stirling]

Drill two holes on the outside. (~5mm) Diamond grit bit in a dremel or something.

At this point you may blow through with some fan, taped to the window. it'll take a few hours to clear.

Now, make 2cm*2cm squares of glass, and silicone round the top three edges, leaving a gap of some 1mm and covering the hole.

This should stay clear almost all the time.

[Ian Stirling]

Just realised, if the glass is tempered, as it may be with newer windows (date?) it'll explode into little bits when you do this. On the plus side, there will be no fog on the bits.

[Al Reynolds]

Don't drill any holes in the window if it's safety or tempered glass!!! Apparently the drilling holes trick only really works if you get it when it first mists up. If there's been any beads of liquid rolling down the inside then the water marks will always be there.

We have discussed replacing sealed units in double-glazing a few times on here, and I have just paid to have a large picture window unit replaced. I would consider DIYing in the future, as the procedure itself was fairly straightforward.

I have put before/during/after pictures on a web page, along with a brief description of the process involved, here:

Reynolds

[Al Reynolds]

when I read my post. It should be:

[john]

Why is perfectly good glass replaced in this age of recycling?

Why can't the panes be separated, cleaned and then re-engineered into a unit?? No glass cutting or supplies needed (other than the edges).

[Dave Plowman (News)]

Think there's an article in the FAQ about how to do this?

[Ian Stirling]

Because getting the panes off is decidedly non-trivial. The glue is rather tenacious. And, you've got to get all traces of it off, or the new pane may fog. And if you just throw the glass in a glass recycling bin, it takes relatively little energy to remake it.

[Andrew Gabriel]

They can if you can take it to a sealed unit fabricator and live with a large hole in the wall until it's done. I was warned to dismantle and clean up the glass myself if I did this, as they may not do that well enough, and it is annoying to have a nice newly sealed unit which is still dirty on the inside. Make sure you record how thick the unit was before dismantling though. I didn't actually do this as the frames needed replacing and the rotten sash boxes removing too, so it was new windows all round.

[chris French]

Stuart Turner (I think) posted some years ago here about how he did this, involving a vacuum cleaner and silca gel IIRC, it all seemed a bit of palaver o me TBH. (Google Groups is your friend)

Yeah it's not hard, though does need doing properly if they aren't to fail prematurley. I really don't think it is worth the effort of trying to repair one TBH, a replacement isn't really that expensive

[Andrew Gabriel]

Trouble is, by the time it mists up, the desiccant all round the separator has already expired. Just drying the air alone isn't going to help for long as it will mist as soon as any more moisture gets in (or temperature drops below dew point). I don't know what desiccant is used, but maybe gently heating that also to drive off some moisture so it can work again would get you a bit more time.

[Ian Stirling]

The idea is to vent it to the outside. I may not have made this quite clear. If you do this, then it is less likely to mist over - as unless it's foggy, the air outside is always at a humidity under 100%. As in most cases, the outside pane will be slightly warmer than the external air, it's therefore not going to be able to condense, if the vents are of adequate size.

[Andy Dingley]

Glass isn't recycled though. If you're lucky it ends up as glasphalt (road aggregate), if you're unlucky it goes as landfill. Very little goes back into glassmaking as cullet, and almost none as primary glass for direct re-melting. Glass recycling _as_glass_ is pretty broken in the UK.

[Steven Briggs]

I keep contemplating this route myself. The large window in the lounge (about 4sqm) is just starting to mist up, and its large size makes it worth "having a go" at a repair. Anything under 0.5sqm I wouldn't bother, as new small units aren't too expensive (£40-50 per sqm I believe).

Plan A is to drop the unit out, drill a couple of holes through the spacer bars and blow dried compressed air (at very low pressure obviously!) through the unit, and maybe warm the spacer gently to attempt to dry out the desiccant. A bit of silicone to bolster the seal if any weaknesses are visible. Bit of a problem though as Axminster no longer sell the compressed air drying doodad I was going to use.

Plan B is source some new spacers strips and rebuild, initially separating the unit by sawing through the old spacer. I agree cleaning the old spacer adhesive off maybe difficult.

[Ian Stirling]

It's very absorbative - to dry it out appreciably, you're going to need to heat to maybe 80C. And evenly, or you'll crack it.

Take a coil of hosepipe. Place in a pan of water. Place the pan in the freezer. Wait n hours. Now, if you don't blow air too fast through the hose, it'll come out with very little moisture in. I've also wondered why CO2 is not used, as it would seem to have about the same performance as argon fill, but at a fraction of the price. I can only assume some issue with Al corrosion in damp atmospheres.

I've done this (to reuse the glass for something else). It's a horrible job. The spacers have some sort of gloopy black mastic on them, which gums up the saw, so it doesn't really want to know. Scratching the glass is easy. ... If I was to try this again. I would build a little wood block or something to hold a stiff blade, like a stanley knife, with a little cigarette-lighter "blowtorch" playing on the blade. In the hopes that running this repeatedly over the edges would eventually get the mastic away, and allow the aluminium to be scored through. Actually, I lie. On reflection I'd use a much stiffer guide, and a 5mm carbide burr in the dremel set at ramming speed.

[Chipmunk]

Argon has a low thermal capacity, even at low pressures, that helps with the loss due to convection from one surface to the other, the saving is probably low, but with larger windows used these days than before, every little helps. Plus, it makes them sound high tech.

[Steven Briggs]

In message , Ian Stirling writes

Ah good idea, I was thinking bucket of water & ice cubes, but of I've got one of those coiled air lines, put that in a bucket / large pan of water and freeze the lot solid. Splendid idea.

[Ken]

I think my windows may well be tempered glass.

Thanks for some really interesting answers from everyone

Ken