patching plywood deck

If a spot of plywood delaminated, the rest is probably not far behind. Meantime, either patch will work for now. I'd go with what you think is easiest.

Vanilla plywood, or what we used to call marine plywood, which had glues that would stand up to moisture? I don't think ANY coating could make regular plywood hold up.

Clean up the hole, soak it with polyester boat resin and allow to cure thoroughly, fill the hole with bondo, sand smooth and paint. Repeat as often as new delamination occurs.

Joe

Yes on the resin, no on the bondo. One lady in spike heels will shatter it. If proper marine-grade plywood no longer exists, coat the patch piece on all six sides with the resin, screw it down, and resin over that.

But like the other guy said, if one spot failed, others are likely not far behind. I'd poke around with an icepick and a bright flashlight before I sank any real time or money in the project. Maybe a quick'n'dirty patch to tide OP over until they can save up for a new deck surface.

Rest of deck is solid, it's just this 1 spot. Maybe cuz of puddling in the low spots which I have no idea how to fix other than rebuilding the entire deck. Anyways, I have tried bondo and it separates from the ajoining wood after a year...best patching material for small areas is construction adhesive - just trowel it on in several layers, Sadly I need to repair spots, mostly rusty nails growing thru the coating, every year. Thanks to the builders who saved $10 30 years ago using nails instead of galvinized screws!