The message
from "visionset" contains these words:

This is to prime the bit of mdf that I've exposed by routing another
profile
over an old one, on some skirting that'll eventually get white gloss.

The MDF primer/sealer I've used was basically PVA. There is a tiny bit
of raised "grain" but then you'd expect to rub it down prior to a finish
coat anyway.

--
Skipweasel
Pay no attention to that man behind the curtain.