I recently made a bench with MDF and when it came time to painting it, I had trouble getting a smooth finish at the ends of the MDF boards – all the paint was sinking into the MDF leaving a rough finish.
Here’s an easy fix I discovered which works like a charm: dilute some wood glue with a little bit of water and apply it with a brush on the ends. Wait for it to dry and then sand it down. Repeat a couple of times until the surface in smooth.
Your paint will glide on easily and leave a perfectly smooth finish!