Trimming flexistrip glazing tape

[mikefab]

I've just had my first attempt at glazing and have had a bit a struggle with the flexistrip butyl tape. I followed the Hodgson instructions and stuck the tape to the rebate upstands so that it overlapped the edge of the rebate by 2-3mm. The next move following pressing the DGU into place and fixing the beading is apparently to trim it with a curved knife (why curved...? maybe something to do with scoring the glass??) and then pull it away. But this seems really difficult. The tape is hard to get away from the glass, and also seems to stick back to itself as soon as the knife has passed through. When I did manage to pick it up and start pulling it away it would inevitably break off at some point and I would have to start again. The only curved blade I had to hand was a scalpel and a little no 10 blade. Maybe this was too small? So it was a right old faff trimming the tape all around, and the finish isn't too great when I look closely. I've found I can smooth it down a bit but I'm still not too impressed.

What am I missing here? I'd be really grateful if someone who uses the stuff could pass on some hints. The (external) beads were siliconed and pinned in place (no space for another tape in the rebate) and this seemed much easier just to trim the silicon when it had gone off.

I'm wondering if it would just be quicker and easier to abandon the tape in future and just silicon the glazing units in.

Thanks for any advice!

Mike

 

[Harbo]

We had some failed DG units replaced professionally and they were just siliconed in and a very small bead of silicon gunned in afterwards to finish off.

Rod

 

[Woody2Shoes]

Can't help with the trimming problem I'm afraid - I've avoided using tape partly for this reason and partly because I imagine future difficulty removing failed units that are effectively 'glued in'. I prefer to use self-adhesive EPDM profiles like this: http://www.exitex.com/joinery-seals-gla ... azing.html I guess my suggestion is probably too late!

One of the things to be wary of is that there can be incompatibility between silicone/other sealants that come into contact with the edge of the sealed DGU (the spacer is glued in with PIB) - some sealants can degrade the PIB and cause early DGU failure. One way round this is to protect the edge of the unit with self-adhesive aluminium foil tape (but you then have additional trimming tedium!).

Don't forget that the rebate needs to be vented and drained and the DGU needs to be on spacers (using the 'heel and toe' method if an opening sash).

Cheers, W2S

 

[RobinBHM]

I've just had my first attempt at glazing and have had a bit a struggle with the flexistrip butyl tape. I followed the Hodgson instructions and stuck the tape to the rebate upstands so that it overlapped the edge of the rebate by 2-3mm. The next move following pressing the DGU into place and fixing the beading is apparently to trim it with a curved knife (why curved...? maybe something to do with scoring the glass??) and then pull it away. But this seems really difficult. The tape is hard to get away from the glass, and also seems to stick back to itself as soon as the knife has passed through. When I did manage to pick it up and start pulling it away it would inevitably break off at some point and I would have to start again. The only curved blade I had to hand was a scalpel and a little no 10 blade. Maybe this was too small? So it was a right old faff trimming the tape all around, and the finish isn't too great when I look closely. I've found I can smooth it down a bit but I'm still not too impressed.

What am I missing here? I'd be really grateful if someone who uses the stuff could pass on some hints. The (external) beads were siliconed and pinned in place (no space for another tape in the rebate) and this seemed much easier just to trim the silicon when it had gone off.

I'm wondering if it would just be quicker and easier to abandon the tape in future and just silicon the glazing units in.

Thanks for any advice!

Mike

There's no need to bed double glazed units, they can sit in dry.

The unit should ideally be 4mm smaller all round and must sit on glazing shims which should be the same size as the unit, ie 24mm shims for a 24mm unit. Narrow shims wont support the outer pane.

You need low modulus or neutral cure silicone (not available in shops).

If dgu's are black taped this is best removed on the glazing side with a knife blade. if units are silver taped that is ok, the silicone sticks quite well to it (still not as good as just the glass).

It helps to put a bead of silicone in each corner of the sash first to protect the joints from moisture ingress, esp bottom corner ones.

Put in unit, shim up so spacer bar lines up with evenly sightline, and make sure you have sufficient gap at bottom.

gun around a continuous bead of silicone, the bead should not fill the gap to the depth of the glass its important to leave an air gap.

Treat the bottom bead differently -this needs to have the back of the timber bead fully bedded with silicone so there is no gap between back of bead and glass.

Clean off silicone when dry.

 

[mikefab]

Thanks for your replies so far.

W2S: I'm using the appropriate neutral cure low modulus silicone (Hodgson U9). I decided not to go the drained and vented route but the fully bedded route instead. The DGU manufacturer is happy to guarantee the units installed like this (for what it's worth).

mike

 

[ColeyS1]

Glazing people we use just bed in dgu units with silicone. Then silicone the gap around the units before capping off the triangular bead that's pinned all the way around.
Yesterday my workmate had to replace a unit that was fitted this way after 9 ish years- it had a ball kicked at it so that probably helped contribute to condensation. He had a few choice words to say about how well the silicone was still sticking (broke unit removing it )

Coley

 

[mikefab]

thanks Coley. I think I probably won't bother with the tape in future.