Do I need to glass in my window backing pads?

[MaxCG]

I'm resealing my acrylic windows which are screwed into ply backing pads. The pads are rotten and need replacing. They are glassed in (see photo). Once I've ground the old ones out should I glass over the new ones like was done previously or just leave bare?

 

[Boathook]

I suspect that the wood gave support to the fibreglass by reducing flexing and allowing the perspex to seal. Could try cleaning up and see how much the grp flexes but feel that support will be required.

 

[William_H]

I would suggest that you get rid of the ply and GRP covering and simply screw the screws through the acrylic in to the GRP. No backing pad. If you really need a abcking pad for more stiffness then add layers of GRP or even carbon fibre. Drill and tap the holes for screws. ol'will

 

[rogerthebodger]

I would not use plywood, I would use hard wood strips the thickness of the ply and the width or the top and bottom of the plywood or wood 44mm wide by 22mm thick

I would glue on the strips along the top and button and both side with thickened epoxy

I would also varnish the wood strips to make then look nice

 

[PetiteFleur]

As William H says, screw directly to the grp but use Butyl tape for a secure seal and use a stainless washer at each screw so the Butyl tape doesn't get entirely squeezed out.

 

[MaxCG]

I would like to sack off the backing pads and screw directly into the hull alone for simplicity, but surely the whole ply + GRP covering must have been used for a reason? Although the need to glass in the backing pads seems odd to me. Surely bonding the ply to the hull with epoxy would be sufficient and covering with fibreglass would just trap moisture? The whole thing is covered by a plastic frame and headliner so aesthetics are not important.

 

[Tranona]

I expect the backing pads are there because the GRP was considered too thin to take screws and/or the cabin side flexed leading to leaks. If the ply is rotten then sensible to take it all off and replace with new but not glass it over. Attach it with an adhesive such as CT1 then paint it with Danboline. If you seal the windows to the hull properly they should not leak and rot the ply.

 

[[193211]]

Through bolt with Interscrews? Depending on the thickness of coachroof, you might be able to go without ply backings altogether.
Self tappers are always going to be problematic as everything expands and contracts at different rates. If the wood gets wet, they’ll pull out.

 

[Stemar]

If you seal the windows to the hull properly they should not leak and rot the ply.

The trouble with that is that windows always leak. If they aren't leaking now, they will.

I'd be inclined to build up a few layers of grp to give stiffness and through bolt, either with interscrews or domed nuts on the inside, which can also look pretty good.

The surround is 3mm ply, but it's easily removable and purely decorative