fiberglass schedule for deck repair

[Xoloski]

Hi, I am relatively new to boats.
I have a 1972 Formula that I am attempting to restore.
The floor was spongy so I removed it from the boat and found core rot in the fiberglass.
The deck board that I removed is roughly 28 inches wide by 8 feet long. I thought I could cup open the deck board, remove the rotted plywood, then refuberglass the new plywood back into the deck floor molded section. The following photos show the deck before, during, and after I cut the top section of fiberglass open and removed the plywood. I came out pretty clean.

I have a few questions:
1) The old plywood looks like it was 3/8 inch pine. I can't seem to find 3/8 marine plywood. Should I just use standard 3/8 plywood to replace the original or is there something better I should use?
2) After I size and install the plywood what order and what materal should be used to glass it into place?
I have read so many discussions that I am confussed. I was thinking:
a) ployester resin to waterproof the plywood and create a base for
b) 1.5 ounce chopped map, followed by
c) 18 ounce roving woven, then
d) repeat this once again, and finally
e) a top layer of mat.
So, that would be chopped mat, roving woven, chopped mat, roving woven, chopped mat.
I have no way of telling what was originally layed up.
Any advise or suggestions will be greatly appreciated.
Besides being new to boata, I am also new to working with fiberglass.
Thanks,

 

[C ☠ dog]

1708 biaxal material and epoxy resin, is it compatible or will polyester resin work better: dissolving glue that binds materials?

 

[Chris1956]

Buy some 3/8 CDX plywood and cut to fit. No one will see it and it is exterior grade. I would cut the hatch opening as well at this time.

Brush a generous amount of slow cure poly resin on the underside of the deck panel and also brush the plywood with it on bottom and sides. A piece of light cloth between plywood and deck panel will help with adhesion, if you have the available thickness. Now clamp and weight the plywood to the deck panel and let cure. Warm temp after a while will help her get hard. Don't skimp on the resin.

Fill any voids between the plywood edges with poly putty and let get hard. Sand smooth and flush. Now cut a some heavy cloth or light mat to cover the plywood, and saturate with more slow cure poly resin and let her harden. Make sure to seal the edges of the hatch opening as well.

Note: Slow cure resin is resin with less than the recommended hardener for the ambient temperature. The slow cure allows the resin more time to seep into the plywood. You will want to add some heat to the panel after a couple of hours, if she is still uncured. Assuming you are working in a garage or outside, a room-temp area wold suffice to cure it. She will harden on it's own, but it could take a couple of days.

 

[kjdunne]

I did a similar project using epoxy instead of poly resin. Search "Best blade to cut fiberglass?" in this forum. I used the West System 105 resin w/ 206 slow hardener, & their 404 thickener between the wood and fiberglass. 6 oz cloth to cover the bottom surface. Very happy with the results and it will outlast me for sure.
Be sure to sand or grind all the old wood residue off the fiberglass panel before installing the new wood regardless of which type of resin you use.