final grain fill done, which filled in some scratches I had not previously noticed.
Sanding done. Waiting for a nice windless day to paint primer on.
I did a test stripe of a scrap of wood, neat cellulose, side by side with the primer plus cellulose. The latter looked better and coverge was noticeably better, although as @Gareth Hughes says, it is very white.I''m going to put two coats of primer on and see whats shines through.