Fixing insulated glazed unit into stonework?

[BigOldMike]

Hi, I hope you are all well.

I will shortly be removing two leaded windows to have them refurbished & encapsulated. They are currently held in by mortar however I don't know how they have been rebated into the stonework. According to my stained glass guru, it's something I'll find out when I chisel away the mortar!

When I come to re-fit the encap units, they will be 20mm thick (as opposed to the single glazed leaded at around 8mm). Does anyone have any recommendations as to the best wat to secure these in place prior to reapplying the mortar? I have been told that adding PVA to the mortar will help it to adhere to the glass but that's about it.

 

[Burnerman]

Hopefully when you get the old unit out you'll find that it has been butting up against a nice flat stone 'land' or rebate - and that will clean up well.
There are several ways of securing the new units.....lets see what the others say but one way is to put a layer of silicone sealer against the land, and at the bottom of the new pane. This should give a nice cushion for the new unit to adhere to, and it'll also take out any roughness in the stonework.
The silicone will hold the pane well, and be weatherproof. I'd be inclined to silicone up the edges to aid weatherproofing before you point up the new unit with lime mortar.
If you come up against anything unusual when the old unit is out, do post a pic.
John