Seals experiments

This is an area I pondered quite a bit. Originally I was going to use sticky both sides glazing tape. having bought some I decided it didn't have enough give in it to accommodate any movement and would be pig to fit. Hence to order for EPDM (foam rubbery) seals, after I'd tested some with linseed oil on them. Compression of the EPDM was the next thing I had to figure out.

As can be seen on the mock up the idea is the inside face of the sash is screwed on to the main sash, holding the glass in place and compressing the seals. The downside to this is the counter sunk screw holes will need filling, but its a compromise I decided to make.

I made up a mock 24mm glazing unit a tested the 3mm EPDM seals I had bought. you can also see the 5mm bridge spacer I'll be using to keep an air space around the unit.

I wasn't happy with amount of compression on the seals, only squashed from 3mm to 2mm. The ridges on seals were only just compressed. So another order this time for 4mm.

This worked out much better, all the ridges are almost completely squashed and the glass is held firmly. I think this should hold the rain out for a good while.

I then did a little experiment to see how muck clamping pressure is needed to compress the seals this much, so I could be happy with the screw spacing.

This showed me that a 200mm length of 4mm seal needs 15kg applied to compress it to 2mm.
I should think this won't be a problem to achieve with 1 1/2 no. 6 screws at 150mm spacing. The clamping wood is 15mm so I shouldn't think it will distort.