Re: Fiberglass Floor Mat Weight
It all depends on how long you want it to last.
The floor (I'll use floor, I know its not correct) in boat can take a great deal of abuse, seats are bolted to it, people walk on it, its a structural member in the design, plus it will have water above and below it much of the time. Now imagine the beating it takes at speed in rough water.
Either type of resin relies on film thickness to prevent water from reaching the wood, with epoxy being stronger, more water resistant, and with a better bond, it will do a better job.
Both work when used correctly though.
If you look at the charts on water resistance for epoxy it shows you need something like 7 coats for it work well, and yes, thinned epoxy is much less water resistant than un-thinned epoxy.
When you need to build up a thick layer of either type of resin cracking can become an issue, a little less so with epoxy, but its still a problem.
Using glass allows you create a thicker layer of either resin and not have to worry about it cracking. It also adds strength to the structure.
People that apply only polyester resin to plywood will be disappointed rather soon when it cracks and peels off, epoxy will last longer, but if the area is stressed you end up with the same results.
When only resin is used on the underside you will never know how well it holds up unless you keep it long enough for it to need a new floor, which is unlikely since people don't keep boats all that long.
If I was going to use plywood as the floor, I would definitely use glass on both sides, its simple, the cost isn't high and there's no downside.
