foam sheet - wet slurry question

hey guys,

just wanted to get a clarification on some great advise from a past post of mine. I will be doing a lot of glass work on a male mold using sheet foam core.
it was suggest to use a wet slurry on the foam panels.

it is all hand work with polyester and "no" vacuum bag

the question is there is a lot of verticale surface work, the sheet is primed with catalyised resin, is it necessary to make a low viscosity putty / slurry and cote the core face and let kick off, or just use the slurry and start the lamination process.

thanks, mark