After chatting with Peter on the blog and looking around on kiteforum, I think I've finally got a way to make the finish in the top of the board glassy right off the table.
If you search 'Porker' on the kiteforum board builders forum you'll find a really great looking board with a gloss finish right off the table. The maker doesn't give any details of the actual steps except to refer to it as 'pre-cured'. Eureka!!!
I'm guessing this just means a light ply of glass layed up on a sheet of plastic to get a mirror smooth finish on one-side, the side that will face up. Once this is cured it can be used just like the topsheet material Durasurf or PBT which has proven very difficult to source in small quantities in Australia.
So my thinking is just wet out a think layer of 3 or 4 oz glass on a perspex sheet, place a layer of peel ply over the top to blot away the excess resin and leave the surface rough so that you get a good mechanical bond when you use it as a top sheet. But wait, here's the rub. If you use clear resin first, lay the encapsulated graphics down ( I've printed them on tissue paper) then peel ply it. Give it a few hours and then apply a coat of white resin , peel ply it again. By letting the clear layer cure first, the white resin over the top of it won't infuse into the graphics like happened to me last time when I only left it a half hour or so. Any the opaque background means that you won't see any of the voids etc in the layers of laminate when it placed on the top in the lay-up.
Bit fiddly but it means that the topsheets can be made in advance and stock piled.