Thanks TIG,

The Coolean plug in finally did work. Also I thought intersect was only in Pro. Ill have to look into intersect some more.

What is the most complex objects that can be used. I am trying to make a vaulted slab but it must be too complex because it will not intersect them. it just creates some strange copies.

If I make a simple square and a cylinder it works

Slab intersect Japan.skp