Prepping MDF Edge for Painting

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
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its ready already

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I usually just boom it good with Krylon primer. Two three coats and let it dry over night and you are ready to go.
I'm thinking you sealed it good enough by now. Give it a rest over night and sand lightly and start painting. Greg
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