"Sealing" windows?

[TobyB]

This isn't woodworking exactly - but it's related ... I'm doing up my wooden french windows - including cutting out a rotten section of the rain sill and replacing it - and repainting.

Having sanded away all the loose paint etc, I'm down to bare wood on all the lower surfaces. There doesn't seem to be much in the way of sealant/putty/etc between the wood and the double-glazing panels too keep out the wet. Can I use something like silicone sealant here - or is there a more appropriate material? Should I apply before or after undercoating?

 

[Joiner]

Be sure they're not dry-glazed with glazing tape, which can give the impression of there not being any seal between the wood and the d/g unit. But whatever is there, you can seal the edges of the bead with a clear sealant, but use an ACRYLIC sealant (it will be marked as 'overpaintable') because silicone will reject any subsequent application of stain, varnish or paint.

B&Q sell the transluscent sealant which goes on white (so you know you've got a good coverage) and dries clear. It's best to apply it after you've treated the windows otherwise, because it dries clear, you'll see untreated areas underneath the sealant.

As the sealant is going around the edge of the bead it won't affect the edges of the d/g unit.