I have used this epoxy/sand mix on concrete floors. it is very heavy and very brittle (okay on concrete), I would think it would tend to crack and flake off in chunks over wood or anything that flexes or changes size/shape with temperature changes. It is fairly costly too.
tiny plastic pellets embedded in paint is a much better option. I have even seen ground walnut shells used in a flexible neopreme paint which is light and watertight, but it is not that durable. the walnut shells seem an interesting and light aggregate, though it seems plastic would not be prone to rotting or trapping moisture.
epoxy paint with tiny short chopped fibers, and either plastic pellets or sand seems it would be durable and light. though it should still get painted over (any color you want) to protect it from UV degredation.
It always strikes me as funny how no one would put varnished wood on the roof of their house, or even fiberglass panels, and expect them to last. but this is commonly done on the cabin roofs of boats and decks (and of course the owner always complain about the amount of maintenance it takes to keep it nice looking). Use the materials commonly used on house roofs and decks and it will not only be cheaper, but also last much longer too.
There is a rubbery weather tight latex mixture called "snow roof" to seal metal roofs, and a similar more durable gray mixture for decks. I always thought that would make a good boat deck coating. It is cheap and easy to reapply regularly. I also like the paint with fine sand in it, looks good, easy maintenance, though paint is not quite as durable something made for deck coatings.
