I'm trying to prepare the edge of MDF for primer and painting.

I've taken the advice from this group and used Glue Size and
put a coat of Drywall Compound on. How do I know when I am done?

I put two to three coats of glue size on each edge. About a 50/50 mix
of water and Titebond III. I assume that can be used.

Then I put a coat of drywall compound on. It isn't totally dry yet but
I test sanded an edge with 180 paper and it is still rough to the touch.

Do I put multiple coats of drywall compound on until it is smooth?

I assume one coat of glue size would have been enough but I did three
before it totally dried.

Going to prime with BIN next. I never painted MDF before, so I have
no idea when the edge is ready.

Thanks

Ken