Hi everyone,
A quick note on fiberglass over foam and compression strength, knees, heels, etc.
I'm not a pro, but I have been shaping my own surfboards for over 20 years and have some experience there. Standard glassing schedule for the top or deck of a shortboard is one layer of 6 oz. and one layer of 4 oz. cloth. Often one of the layers will only cover the area of the deck on which you stand. The bottom of a board is typically glassed with one layer of either 4 oz. or 6 oz. cloth. Adding a gloss coat of resin over the laminating layer (as opposed to a sanded finish) may help resilience a tiny bit, but comes with more weight. Competition boards will have lighter glass and are considered semi-disposable, since professional surfers are sponsored by their surfboard manufacturers.
Even with the two layers of cloth over foam, dents from knees, heels, and even bony ribcages are so common as to be considered inevitable (referred to as "pressure dings" - dents that don't puncture the glass and thus don't break the watertight seal).
Since I hate sanding fiberglass more than I hate sanding wood, I have moved to vacuum bagging wood or cork skins over XPS foam for my boards. In my own experience, 1/8" plywood over foam is significantly more resilient in terms of compression strength than fiberglass, and laying up a sandwich panel for a floor would likely be simpler to construct as well as less expensive than to glass it.
If you're interested in the process for skinning a foam surfboard with wood skins, check out this blog post by the very kind master craftsman Grant Newby, whose process I now use Though I can't get hold of milled paulownia skins and use poplar bender ply instead. Might give foamie builders some interesting ideas!
https://woodensurfboards.blogspot.com/s ... vacuum+bagTT