Hi Koi,

re:
> I´m not sure what you mean.. Actually I built that solid ffrom a surface with ´shell´. Firstly I tried
> to built it with profiles and networks. When I joined them in the end, I just got a joined surface
> every time..

The way Shell works for thickening an open surface is it builds a surface offset and then connects the edges.

Instead of using a surface offset method (including shell) it could be better to draw a second set of curves for the inner surface, creating it in the same way the outer surface was created.

- Michael