Advice needed, any boatbuilders out there?

[melandnick]

I have rot in the coachroof sides where water has got in around the portholes.
The sides are in 12mm plywood with a 1.5mm ish veneer on the inside which is now painted.
So I have 13.5mm or so as total thickness and I have some spare robbins elite 6mm ply.
I cut out the rot and then routed the inside to a depth of 6mm to give an overlap so that I can patch the hole in 2 pieces.
My question is:
Is there any reason that I cannot epoxy a couple of layers of 3ooG glass fibre mat in between the two ply sheets? I figure this would make up the thickness to about what I need and should make a very strong repair without needing to fair off any rough epoxy.

PIC OF HOLE CUT TO CLEAR THE ROT:

PIC WITH PATCH IN PLACE WAITING FOR GLASS THEN SECOND OVERLAPPING 6MM PIECE:

HOPE THIS MAKES SENSE OF IT.

Thanks

Nick

 

[ccscott49]

I'm not a boatbuilder, but sounds a good idea to me, bond the two patches together with epoxy and cloth to get the right thickness, then fit the patch. Or could you source some 1.5mm thin ply or veneer and bond that lot together? Mind you thinest ply I've seen is 2mm.
venner available on e bay cheap enough. But normally .6mm thick.

 

[oldsaltoz]

I would not use cloth between the ply sections.

I would install the outer patch first making sure it's 100% in line, then dry fit the internal patch, remove it and drill 8mm holes about 25 mm apart, then add some epoxy mixed with Micro-Fibres and offer up the new patch, the holes will allow any trapped air and excess material to be squeezed out, more importantly it will allow you place the patch 100% at the required level.

Good luck.

 

[ccscott49]

I would not use cloth between the ply sections.

I would install the outer patch first making sure it's 100% in line, then dry fit the internal patch, remove it and drill 8mm holes about 25 mm apart, then add some epoxy mixed with Micro-Fibres and offer up the new patch, the holes will allow any trapped air and excess material to be squeezed out, more importantly it will allow you place the patch 100% at the required level.

Good luck.

Bloody good idea that!

 

[melandnick]

I would not use cloth between the ply sections.

I would install the outer patch first making sure it's 100% in line, then dry fit the internal patch, remove it and drill 8mm holes about 25 mm apart, then add some epoxy mixed with Micro-Fibres and offer up the new patch, the holes will allow any trapped air and excess material to be squeezed out, more importantly it will allow you place the patch 100% at the required level.

Good luck.

Pretty much what I was planning.
but why would you not use the glass to reinforce it?

Nick

 

[oldsaltoz]

I would not use cloth primarily because you can't always get it flat enough so you risk leaving a void under the window,

The mix of resin and Micro fibres will completely fill the void and any excess will fill the holes drilled.

This method also allows you to position the ply in exactly the right place, flush so little or sanding required.

Good luck.

 

[melandnick]

I would not use cloth primarily because you can't always get it flat enough so you risk leaving a void under the window,

The mix of resin and Micro fibres will completely fill the void and any excess will fill the holes drilled.

This method also allows you to position the ply in exactly the right place, flush so little or sanding required.

Good luck.

Great
Thanks for the advice

Nick

 

[TQA]

I'm not a boatbuilder, but sounds a good idea to me, bond the two patches together with epoxy and cloth to get the right thickness, then fit the patch. Or could you source some 1.5mm thin ply or veneer and bond that lot together? Mind you thinest ply I've seen is 2mm.
venner available on e bay cheap enough. But normally .6mm thick.

These guys stock ply down to 0.4 mm

http://www.happyhobby.com/hobb_html/birch.htm

But I agree use some filler in the epoxy and clamping to get the the correct thickness would be easier. Some cloth would not hurt but I do not see it as being necessary.

 

[Thunderbird7]

If you use cloth and don't get it completely flat, you could get air pockets that become traps for condensation leading to de-lamination later and then you would have to cut out.... see above

 

[melandnick]

If you use cloth and don't get it completely flat, you could get air pockets that become traps for condensation leading to de-lamination later and then you would have to cut out.... see above

Problem is that exactly the same applies if I use thickened epoxy on its own.
If anything I think it’s easier to build up thickness with cloth and less chance of voids than using thickened epoxy to give the space I need between the ply sheets.

Anyway, that’s how I did it (yesterday) and its all well clamped, staples and screwed together with just enough pressure to minimise voids but not too much otherwise I lose all the epoxy out the sides.

Thanks guys for the input on this.
I went for the solution that I believe to be the strongest in the long run.

Nick