One very good advice............
Ever thought about covering you scenery with filler, sand this down slightly with sandpaper grade 240 and then painting the model...
Cause I guess you mean smooth as in "not as shiny as it will flash your eyes when light passes over it".
My old favourite is a very thin layer of PVA glue mixed with ultra-fine sand. Apply this, wait for it to dry and then sand it down with fine sandpaper, as Dragonslayero recommended. You need to be careful and not put on too thick a layer of glue/sand mix though. Believe me, I've been down that road and it always ends up in comments like:
"That's a nice boulder."
"That's not a boulder, it's a bunker!"
"Really? You could have fooled me!"
"Look, do you want to continue using my front room for games or..."
A forum community dedicated to Wargamers, Wargaming 40K enthusiasts. Come join the discussion about Warhammer and Wargaming collections, miniatures, tactics, terrain, reviews, accessories, history, displays, models, styles, scales, reviews, accessories, classifieds, and more!