What material for backing a large fibreglass repair?

[Polly1]

Hi
The previous owner of my boat cut an extra wasboard into the entrance that I wish to glass up. The entrance wall is about 1cm thick solid fibreglass. To save on resin and cloth and to support the repair I was thinking of using a perspex plate in the centre as a sandwich and then glassing the front and back.
I thought the thermal expnasion of the two mught be a little different but not enought to matter.
Any thoughts on this idea as a suitable repair or alternative materials?
Thanks

 

[Deleted member 36384]

I would buy a GRP panel and bond that in.

 

[Poignard]

I would buy a GRP panel and bond that in.

+1

 

[macd]

Any thoughts on this idea as a suitable repair or alternative materials?

Why not use the proper stuff? Lightweight PVC foam or even paper honeycomb are designed for the job. Available from any good specialist GRP supplier.

 

[fisherman]

Many things from ply through foam, balsa, to nidaplast that are better than perspex, which is in no way designed for this job. If you could get a small pice of Nidaplast that would be great, but a full sheet is too expensive. Otherwise just lay up a sheet of grp on a flat surface with plastic sheet on it for separation, then bond it in.

 

[PaulRainbow]

Assuming no structural strength and that there has most likely just been a ply panel as a washboard, use a piece of ply and glass over it.

 

[savageseadog]

Assuming no structural strength and that there has most likely just been a ply panel as a washboard, use a piece of ply and glass over it.

I agree. A plywood panel embedded in the lay will do well. Balsa would be stiffer and lighter though.

 

[Polly1]

Thanks for the replies maybe I will just glass in the old ply washboard

 

[vyv_cox]

Polyester resin does not adhere all that well to plywood. To give it a decent chance remove any surface varnish, wax, paint or dirt, roughen it up with coarse abrasive paper before glassing. My wheelhouse is plywood with a grp layer on top. The whole lot disbonded and had water beneath it. I replaced it with epoxy and glass, which is very well adhered.

 

[fisherman]

Polyester resin does not adhere all that well to plywood. To give it a decent chance remove any surface varnish, wax, paint or dirt, roughen it up with coarse abrasive paper before glassing. My wheelhouse is plywood with a grp layer on top. The whole lot disbonded and had water beneath it. I replaced it with epoxy and glass, which is very well adhered.

It can, without too much difficulty. I skinned my wheelhouse with extra ply and bonded it to the deck in 1995, it has been intermittently under water since then with no problems. The trick is to paint resin onto the abraded ply first, then start again with another layer of pre-wetted resin and mat. it's the same as wetting a wall before plastering. None of my work with ply has disbonded to my knowledge, including a hauler cabinet from 1983.

 

[vyv_cox]

It can, without too much difficulty. I skinned my wheelhouse with extra ply and bonded it to the deck in 1995, it has been intermittently under water since then with no problems. The trick is to paint resin onto the abraded ply first, then start again with another layer of pre-wetted resin and mat. it's the same as wetting a wall before plastering. None of my work with ply has disbonded to my knowledge, including a hauler cabinet from 1983.

I should add that the wheelhouse was not built by me! Judged by the workmanship on many other parts of the boat the person who did it was not very competent. I agree with your method, which I have used myself.