Adam wrote in message
The big advantage that stands out with the ifpsl stuff is that they
supply a carrier for their parting bead, which can be screwed into the
slot left by the old parting bead. This may be much easier than using
mastic or similar if the slot is too wide (as it seems to be with our
windows).
That looks a very useful product. One of the major probs with renovating
sliding sashes is that if you strip all the paint off the top one you end up
with a big gap between the parting bead and the outside edge of the box.
Short of moving the groove or thickening the exposed part of the bead, there
ain't a lot you can do except put up with the rattles and draughts.
I have my doubts about the top and bottom seals. All the flexi polymer
things I've tried have ended up permanently flattened when kept under
pressure for weeks at a time in the winter. IME the only thing guaranteed to
keep its springiness is a hollow silicone bead (can't remember who makes
them) but the slot to take it can't be routed into existing frames.
I think if you solve the parting bead problem and the staff beads on the
inside are carefully positioned you can eliminate most of the draughts and
rattles. Also, too many retro fit seals on old windows look a bit naff IMO.