can a mesh be smooth without creating "holes" Right now I try to smooth a quite big mesh to the piont you cant realy make out the eges in the final rendering. But every methode I found was just giving no result at all or downsize the singel "mesh tiles" and by that create holes in the mesh. From my understanding i need to enlarge the mesh "resolution" witch i tried with multires BUT the simple setting does nothing at all in my case and the Catmull-Clark setting creates the mentioned holes.  

Original object


Catmull multires
As @RobertGützkow pointed out, this is caused by disconnected vertices.


Select all vertices (Select > All), A
Go Mesh > Clean Up > Merge By distance, Alt+M
Done.