So I was working with drywall this weekend and I got to thinking about how did the ancient plasterers get their plaster so smooth. From my understanding sandpaper is a fairly modern invention. Did they use sharp chisels to take off high spots after it hardened? Were they just that good that they didn't need any post work?
I mean really, they were working with materials that are far less forgiving than our modern blue board or drywall and yet you see some fabulous results.
Practice.
Plastering is a perfect example of one of those things where you see a pro do it and it looks easy, but when you try to do it yourself, it turns out to be impossible.
Plaster is a bit different than joint compound. It's put on in two or three layers, with the final layer being a fine mix. It is usually leveled out by using a sponge-float (which may or may not include a bit of sand) on the nearly set plaster.