Replacing a DG unit.

[John Brown]

I have a fogged DG unit, and I'm planning on replacing it as soon as the weather improves. It's fitted in an oak frame, with oak beading pinned on outside. I've never done this before, as all my previous dwelling were single glazed. Can anyone advise me on the correct methods, or point me at a useful guide? One thing I'm a bit concerned about is possibly having to buy miles of sealant strip and only using a few metres.
P.S. If it makes any difference to the procedure, it's a non-opening window.
P.P.S I just checked out Flexistrip prices, and it seems my fears were unfounded. I probably saw a price for a giant roll somewhere, and got the wrong end of the stick!

 

[deema]

I’d use 3mm security tape on the frame, pop the double glazing unit, which will stick like glue to the tape. (Make sure you add glazing [plastic] spacers so it’s centred) Low Modulus silicone around the double glazing unit. Bead of silicone around the glass and the frame and then stick in the beading. Pin if the beading needs it. I try not to pin, makes it far easier to reglaze with no down side IMO. Just check that the silicone is compatible with DG units, some destroys the seal.

 

[rogxwhit]

Low Modulus silicone

Low modulus neutral cure silicone ... is the ticket.

Use stainless (or brass) pins if you need to replace any. 30mm is a likely length but it depends on the bead height.

 

[okeydokey]

Wherever you buy the glass/window will advise the best way of fixing and most probably provide suitable lengths of tape or whats needed for negligible extra cost. I have bought replacement units from a local double glazing firm who were happy to help - they make a profit on the sale without any effort, Take a photo of the window in position it might help

 

[Doug71]

Wherever you buy the glass/window will advise the best way of fixing and most probably provide suitable lengths of tape or whats needed for negligible extra cost. I have bought replacement units from a local double glazing firm who were happy to help - they make a profit on the sale without any effort, Take a photo of the window in position it might help

My local glass supplier (who I don't use as they are useless) supplies people with the wrong type of silicone.

I pointed out to them that it says on the tube something like "not suitable for use next to double glazing edge sealant", they told me that's a load of rubbish, it's all the same and the manufacturers only puts that on so they can charge more for the other stuff

This is the silicone I generally use

https://www.reddiseals.com/product/silfix-u9-sealant/

 

[rogxwhit]

Dont forget when sizing the glass that you need a gap (about 4mm should do) all round the unit, and it mustn't sit on the rebate at the bottom but rest on spacers. Not all frames are silicone glazed - some use dry glazing, but with that method the rebate must be drained ...

Also be aware of glazing regs regarding where toughened glass should be used ... (google it) ...

 

[eribaMotters]

Working from the inside, make sure everything is clean dry and primed. Sit unit on glazing blocks, fix into place with 12 x 3 mm double sides glazing tape, smear of butyl putty on the face of the internal glazing bead and on the top edge of the outside trim to cover the raw edge of the tape and throw any water.
I would not use silicon as paint does not like sticking to it and as mentioned above silicon can effect the DG seal.

Colin

 

[John Brown]

Working from the inside, make sure everything is clean dry and primed. Sit unit on glazing blocks, fix into place with 12 x 3 mm double sides glazing tape, smear of butyl putty on the face of the internal glazing bead and on the top edge of the outside trim to cover the raw edge of the tape and throw any water.
I would not use silicon as paint does not like sticking to it and as mentioned above silicon can effect the DG seal.

Colin

There is no paint, the frames are just oak.

 

[John Brown]

Thanks to all. I think I have enough advice to feel a bit more confident about this task.

It's a funny thing, in my late teens through to my forties, I imagined that I knew how to do anything and everything, and generally muddled through.

Now that I'm an old fart of 70, I have a tendency to overthink things, and spend ages researching(OK, googling)stuff.
In a logical universe, I'd expect the opposite to apply.

 

[Richard_C]

When you order you need to be clear about the measurements you give. It's either the size of the recess, in which case they make the allowance and provide something a little smaller, typically 4 to 6mm all round, or the actual glass size you want in which case you have already made the allowance. If they add their allowance to your allowance you end up with a unit that is too small. How do I know this? Not telling.

 

[ian33a]

Generally, you measure the rebate in X and Y and subtract 10mm from each. That becomes the dimension of the glass. That said, if the beads are skinny, most units have about 11mm spacer bars around the outside and an associated primary seal. You don't want the primary seal to be exposed as it quickly degrades in sunlight and looks horrible if it is visible. Some companies will sell units with a skinny spacer bar (for heritage windows) but these don't tend to last as long as the standard units. You really want the units sized so that the spacer bars sit just inside the bead edge - but the gap around the outside is important.

As others have said, the units need to stand on spacers at the bottom. This sets the sight lines correctly but, more importantly, keeps the units from sitting in water if water gets behind the beads.

You can attach the units to the face of the rebate either using galzing tape (and the spacers) and this will hold them in place. Equally, you can attach them using silicon. A thin layer all around the edge holds them in nicely.

As for the beads, dry glazing is simply that you nail the beads into place. Water will drain off the units and down into the bottom of the bead. It's vital to ensure that the water can vent away, otherwise it will puddle and rot the bead and the unit. Generally, a nailed in bead is enough but vent holes to the bottom of the frame are preferable.

Personally, I prefer a wet beading. I run a continuous line of sealant all along the inside of the bead (where it contacts the window) and then nail the bead into place. I do not put sealant in the gap between the bead and the frame as this provides a water channel (to some degree) for any water that does find its way behind the bead to escape.

Some people put a bead of sealant on along the line where the glass meets the bead. I find that unsatisfactory as it's always too thin and prone to coming a way.

Low modulus silicon sealant is what should be used. The silifix U9 is good stuff but most decent brands (such as Soudal or Dow) should do a reasonable job. Don't buy really cheap sealant, it's false economy.

 

[Doug71]

Here is Hodgsons recommended system if using Flexistrip

https://woodenwindows.com/media/resources/WW-hodgson-glazing-guide.pdf

 

[scholar]

I am replacing some external window heading (and have a blown DG unit to replace). I found this video from Ollie Bradshaw very helpful and am following his technique.



Cheers

 

[John Brown]

Thanks. His use of silicone differs from the Hodgson method.

 

[scholar]

Thanks. His use of silicone differs from the Hodgson method.

The windows I am working on were glazed it seems with the Hodgson method. The silicone bedding seems to have worked well, but the glazing strip is problematic - I dont actually know, but likely it is Hodgson’s Flexistrip or something similar - this seems to remain non-setting and sticky.

The two problems I am dealing with are:
- some of the internal glazing strip has seeped out from under the beading where the windows are exposed to full sun; and
- on the external bottom and overlaid muntin beading, the seal between the glazing strip and glass has started to fail resulting in a build-up of black staining visible from inside - whilst the beading itself is ok, I am having to remove it as just sealing over the glazing strip would leave the unsightly staining visible.

The windows are rather overdue for repainting (about 16 years since installation), but these problems have been apparent for a long time.

So I am hoping that the Bradshaw method will prove better. I am thinking I will need to gouge out a few mm of the gooey glazing strip all round and add a Hybrid polymer sealant to the edge as per the Bradshaw method (this is going to be very tedious).

Cheers

 

[RogerS]

When you order you need to be clear about the measurements you give. .....

Oh dearie me...yes. I was renovating a house, measured the window sizes for the units, ordered them from a local DGU firm...good prices and qualty. After a few days rang 'em to ask if they were ready. "We've done one" she said "but would like you to check it before we do the rest".

I popped round to see them. "I'll go and get it," she said and returned empty handed...well, her hands were behind her back. Smiling she brought out this perfect miniature DGU 'cos this muppet had dropped off the hundreds from the measurements We did have a good laugh, though.

 

[John Brown]

Just decided to start this, as weather looked helpful. Naively hoped to be able to remove external oak bead... No chance! Silicone everywhere! Removed bottom bead in splinter sized pieces with brute force and old chisel.
Any tips on the best way to remove? I'm happy to make new beads, and I have an oscillating multitool. I'm thinking of using the multitool between bead and frame, but wary of using it between bead and glass. Help me!!

 

[deema]

I use a Stanley blade or a very flexible scraper to run around the beading next to the glass. This cuts through the silicone. I then use a glazing knife or glazing hacking knife and force it in between the frame and the glazing bead. I usually try to push it in either end and in the middle, or between where I think the nail pins will be located. usually takes a bit of effort to start lifting the beading. The Hacking knife is hammered to cut the nails for the first head.
If you have cut the silicone against the glass the bead will pop out in one piece. The remaining beading is rinse and repeats and are usually very very easy compared to the first one that’s usually sprung in.
I usually try and start with the longest side which allows the beading to flex enough to come out of the mitres in the corners.

 

[ian33a]

Exactly what Deema said. Just take your time. If there is a load of silicone between the glass and frame, use a knife to cut away as much of that as you can before trying to remove the glass. There should be little or no old silicone remaining when you start to put the new unit in.

 

[scholar]

I have been doing this recently, removing some of the beading on DG units that are being retained.

I have been putting a piece of 6mm ply on the glass and then using the multi tool carefully to cut the beading at an angle a few times - this allows me to use a narrow chisel to remove a section and then attack the beading end-grain on - after a while you get where the pins are going to be and can cut accordingly with the multi tool.

I have done a load of windows flat on the bench, but now have to do some in situ for which I will need an extra hand or two.

Have fun.