MDF Signs - finishing tips beyond use of shellac and type of paint

I’m making my first MDF signs and after reading the previous articles and after I cut them out, I used shellac to seal the wood. It was brush on shellac out of the can, not the spray stuff. The problem is it makes the surface rough and I’m not able to get in there and sand everywhere. The parts not cut are super smooth. On my 2nd sign, I used 2 coats of shellac as a sealer with the same effect, only rougher.

I’ve not seen much info on finishing MDF past the use of shellac and not using the .99 primer. lol

Do you guys sand after applying the sealer? What grit? 220 doesn’t seem to quite get it good for me.

Any tips are appreciated! thanks.

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I sand mdf with 220 and spray with rustoleum automotive primer, 2 coats on the sides let dry a few minutes between coats. Let dry overnight and sand with 220. Comes out very smooth.

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Sanding sealer has worked best for me.

I’ve used sanding sealer with good results and just tried the rustoleum enamel primer a couple weeks ago. I use the little dremel buffing/sanding wheels to get down in the carving smooth if need be.

I thinned my shellac with DNA. Will try the steel wool.

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