visionset wrote:
In the archives this subject is pretty well covered.
It seems an equal spilt between water and oil based primers.
My inclination would be to opt for oil based.
We all know MDF swells after water contact, so for that reason I'd not go
for water based.
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.

It does swell slightly, but shrinks again later.

So either works. Ive used emulsion, acrylic wood primer and sometimes
oil base. I like the acrylic water based the best.

You MUST do at least two coats on the 'end grain'..sanding between coats.