Cutting ply for deck repair

[FinesseChris]

Hi everyone
There's this great big, very expensive sheet of ply from Robbins cluttering up the place, and I'm going to have to muster the courage to cut it up....

Can anyone point a novice towards advice on:
a) cutting, presume a jigsaw will do it but any ideas on blades?
b) (and most worryring) taking a template of the odd-shaped side deck void -- it's about 240 cm long -- so I end up with a piece of ply that fits. Would I be better off in 2 or 3 bits, accepting the downside of joints?

Any advice or recommendations gratefully received.

Chris

PS Might add that I intend to cover ply with epoxy and cloth.

 

[tritonofnor]

I did a similar, though smaller job last year. hacked out all the rotten wood with a chisel, and then treated the end grain with Ronseal wet rot hardener. Then made a basic card template, which I used to cut out the ply. Used a Japanese pull saw to cut it - nearly as fast as a jigsaw, with no tear out. Then it was out with the block plane and chisels. Trial fit, trim, trial fit, trim, ad infinitum (or so it seemed).
To fix it down to the deck beams and carlins, I first laid a bed of epoxy stiffened with colloidal silica, and then through nailed the ply with bronze ring nails. Any edge gaps were sealed with the same stiffened epoxy. The final covering was glass mat, two coats of epoxy, then deck paint. That moved the drips from over my computer, to over the sink! As far as I'm concerned - success!!
If you do decide to do the job in bits, then consider good scarf joints, but I think this will make the fitting even more difficult. I'd try it in one, with a helper to get the alignment right as you trim..
Good luck!

 

[andrewbodenham]

Unless you're really confident this is the sort of job where time spent in templating will really pay off.
Template first in cheap material such as hardboard, or 4mm or 6mm mdf. Your first template might be in pieces, screwed together as the mark-up proceeds. Use this first attempt to cut a one-piece job, still in mdf. Repeat until perfect. Only then transfer onto the plywood, clamping during marking to avoid accidental slips. For cutting I'd second the advice about using a Japanese saw - though you don't say how thick your plywood is. If you have the kit you could cut a little over-size, then trim to your template with a bearing guided cutter in a router. You won't get a better finish or more accurate job than that.
Putting the ply down in one piece has to be your goal, as good joints are time consuming, and will always be a potential source of future problems.
Good luck!

 

[burgundyben]

You may find that once you have templated the piece you require and marked out in pencil your cuts that a score through the top veneer with a sharp stanley type knife will prevent the wood tearing up on the peice you require.

Not sure if I explained that very well.

 

[jhughes]

The stuff they make house for sale signs out of, thin corrugated plastic, makes excellent templates, it can be cut with scissors and is easy to bend yet more rigid than card and waterproof.
The 6' by 3' sheets of brass I use come protected by the stuff but I have also seen it in bins/skips at estate agents and printers.