Fixing polycarbonate sheets in window frames

[Peter Percival]

Can the same putty used to fix polycarbonate in wooden frames as one would use for glass?

[Tim Watts]

On Tuesday 23 July 2013 13:59 Peter Percival wrote in uk.d-i-y:

It will probably work - except that the plastic will flex more than glass and thus is more likely to open up cracks at the putty joint, letting in water.

Is that likely to be a problem?

[Peter Percival]

Could be. I'm glazing (or whatever the word is) a shed. How should I fix polycarbonate sheets? Or maybe you think glass would be better?

Two follow up questions: how do the costs of glass and polycarbonate compare? How do their strengths compare?

For a shed, I'm not bothered with matters aesthetic.

[John Rumm]

Probably not - the poly will expand and contract several mm as it temperature cycles (assuming reasonably long lengths of it). Hence why most fixing systems for it trap it under a rubber seal so that its still free to move slightly. You may get away with more rigid fixing on smaller sheets.

[John Rumm]

If you mean the flat twin (or 3/4/5) wall stuff, then its fixed with glazing bars. These are ali channels that screw down to the rafters, the sheet is then laid into the gap and plastic caps tapped into place on the tops of the channels. You normally need a proper fixing (screws or bracket) at one end to prevent the panel creeping out the end.

If you mean the corrugated stuff (like onduline), then its fixed in the heigh point of the profile using rubber capped screws.

Poly is quite pricey, but very strong, and you can chose various types of finish (clearish, frosted, bronzed etc)

[Tim Watts]

On Tuesday 23 July 2013 15:02 Peter Percival wrote in uk.d-i-y:

Oh - that's easy then.

Stick it in with a bead of glazing silicone (clear) and use 4 wooden beads with panel pins to complete (with more silicone) - the latter leads to a neat job and holds the plastic whilst the silicone cures.

Flexible, waterproof and much easier than putty.

[Brian Gaff]

Also, wheras glass cracks if the frame moves the Pc sheets seem to turn into Rolf Harris Wobble boards after a few years! Brian

[Peter Percival]

Thanks, that's what I'll do.

[John Rumm]

Keep in mind you need to use natural cure silicone, since the acetic cure will cloud polycarbonate.

[Peter Percival]

I'm glad you mentioned that because I wasn't aware that there were two kinds!

[fred]

Watch out too for cheapie places like toolstation (or used to be cheapie places like screwfix) not always stating the cure of their of their silicone products or incorrectly stating 'suitable for glazing' on acetoxy cure when it is not suitable for sealing double glazed units[1]. Make sure it actually says neutral cure and if it has been misdescribed (acetoxy smells of vinegar) then take it back.

Another alternative is to use glazing tapes to secure the poly. Double sided security glazing tape[2] first to secure the poly to the frame which stops casual removal by scrotes then use single sided tape glazing tape stuck to the glazing beads which complete the seal when you tap and tail them in. IMV an easier task with less wet work but I have the tapes in stock here.

[1] I assume this is due to the risk of corrosion of the aluminium tape frequently used over the sealed edges or of the aluminium spacer bars. [2] Smooth foam tape usually about 2mm thick with strong permanent adhesive on both sides. [3] Thicker foam tape, 3-4mm with adhesive on one side and ridges on the other side to enhance the sealing effect when compressed.