Boolean union deleting surface

I have two surfaces which I want to create a union with. The computer either gets stuck “creating meshes” or it seems to delete one of the surfaces. I’m Rhino 5 windows 7.boolean problem.3dm (111.9 KB)

One of the surfaces is a a solid, the other is closed but open on the ends. Rhino is not recognizing that the one surface is open on the ends so it is deleting the “Interior” part of the other surface. Also the desired result would have non-manifold edges which Rhino does not like and tries to avoid creating.

BooleanUnion works if thickness is added to the outer “frame”.

More on Boolean operations:

Booleans are really solid spatial operations. They work on non-solids by, conceptually, considering a non-solid to be part of a larger solid. The union of two sets is the set of everything contained in either of the original sets. Since the solid object is completely contained in the 4-sided thing, the correct result is just the 4-sided object.

Thanks David have got it to work. thanks also for the link, very interesting create awsome stuff before its too