Maybe I'm using the wrong terminology, but it's essentially an epoxy coated plywood. You see it used a lot in cabinetry. It adds an extra 1/8" and some weight to the board.
This is a new table I just recently made, that's why it looks soo clean. I had a problem sealing the overflow on my previous attempt, but so far with both tables the epoxy and plywood have been water tight !
I've only had two minor problems that I would like to resolve in future builds.
a. My drain is sealed with an o-ring seal and doesn't sit flush with the bottom of the table. Even though the table is on a slight incline, a little bit of water builds up around the drain and eventually algae builds up. I either need to work on recessing future drains or adding pumice to the bottom to soak up extra water....
b. I forgot what 'B' was. I'll post later....
Suggestions welcome.