Use Exclude Srfs in the Properties menu to separate some of the imported surfaces after they have been joined using Join Surfs, or specify surfaces to which Join Surfs should not be applied.
Use Exclude Surfs to select surfaces to be excluded from a topology. You can add or remove surfaces from the excluded set.
Some surfaces may appear joined with the quilt even after exclusion. These surfaces can be excluded only in groups because they were joined as a quilt during import.
The original surface is broken down into multiple surface patches because of discontinuities in surface curvature or tangency, or both. These surface patches are not individual surfaces. You cannot completely exclude them from the quilt using EXCLUDE SURFS.