I paint tons of MDF. I use an acrylic primer (interior house primer), but you can use an aerosol primer. Typically I’ll brush the edges first and the spray the whole thing.
The next step is important, sanding! I use 220 to smooth all surfaces as the MDF will soak in the primer and become rough. I then prime again. Sand once more lightly with 220, not too aggressively though just enough to smooth out and small bits. If you are going to use a gloss, I’d suggest using 0000 steel wool to get all the scratches out.
Then paint with your desired color, I usually do a minimum of 2 coats!
These puzzle had 2 primer coats, sanded, at least 2 color coats and then a couple coats of water based Varathane clear satin. I use a HVLP spray gun which works great!
Good luck, with your project, it looks great!
