I want to make a beach pebble mosaic table. Pebbles stuck to an mdf board with a holding timber frame/barrier creating a tray depth of 40mm. Some pebbles will sit higher than others. Maybe some smaller pebbles will be glued on top of each other to reach a max height of, say, 35mm. Can I then pour resin in one go (I am assuming GlassCast 50 would be most suitable) or should I build it up in two or more layers. And finally would it be advisable to use a top coat of GlassCast 3 to give the best finish?