I'm not sure what the original construction layup was, however, recommended weight for deck repairs would be approximately 20oz for the outer skin (example, a 17oz biaxial with 3/4oz mat on both sides). Something thinner for the inner skin would suffice (10oz cloth with 3/4oz mat on both sides), except in highly loaded areas.

I'm not sure how much mat would be required for a pure mat repair. However, it would be straightforward to make some test pieces.

Most importantly: use vinylester or equivalent for repairs, not epoxy. It is much easier to work with, and future vinylester repairs may not work as well on epoxy. Unfortunately vinylester is not readily accessible in small quantities (Svendsens has it by the gallon).

--brendan