Mesh thickness for 3D Printing

I found lots of topics regarding adding thickness to a mesh, but still can’t solve my problem. I basically have the mesh and I want to add flat base (thickness) to it. Projecting mesh boundary points on a plane an connect them into one mesh.

I found a way to convert all of this to a solid but it only works with small meshes with huge terrain it takes ages to calculate “face boundaries” component.

Any ideas for more efficient way of doing it ?

Cheers (634.9 KB)

I have done that but I have still some problem at the base. E1 must be empty for a closed mesh. Perphas repair that in Rhino ?? (638.0 KB)

Thank you Laurent Delrieu! Working with meshes is a pain.

Meshes are fun :slight_smile: (1.2 MB)