Hi,
in the marine industry there is a high build polyester resin type paint that you can spray(preferably), or brush on, and it dries quite hard and can be rubbed smooth (with wet and dry) and polished
to a high degree. Its used to make fibreglass molds and is presents a perfect surface for release wax and/or PVA.

I used to buy a litre at a time from a place that made fibreglass body panels and flairs for cars, it cost 20 bucks or a box of beer. Great stuff.

Craig