Here's 800 lbs on my old club layout.
One of the other advantages of structolite or whatever is that it has TEXTURE. The plaster has ground up cork in it (lite) and that gives it strength (like straw in adobe bricks) and the texture. Yes you can smooth it but use a stiff brush and stipple it as it sets up it looks great. Second big feature is long pot life 20 plus minutes compared to plaster ? ? ? ? Russ