Adding thickness to 3D Scan of face in Blender So I have a 3d scan of a face, pictured: 



And it has no thickness whatsoever, I'd like to add some so that it can be 3D Printable (my printer can handle the vrml/obj format and tons of colors).  I've tried solidify but it puts a bunch of cracks through the face:



And I've tried using the bisect tool, then hitting f to fill the holes while what I bisect'ed was still selected, and all of the holes won't fill.  I've also tried some of the solutions from this question: How to make a perfectly flat bottom for 3D-printing topographic relief?
but it creates those same cracks.  

Lastly I've tried selecting every vertice and extruding backwards, and whatever this is happens: 

Any ideas?  I'm sorry if this has been answered somewhere else.
The 3D print plugin is nice for fixing up a mesh but otherwise I used to just use the decimate modifier and create a new mesh from a scan mesh. Also make sure you've tried selecting all vertices in edit mode and using the 'remove double vertices' function (or remove doubles in 2.79). Then using Crtl + Shift + N to set the normals (untick that box in the bottom left corner though) (in 2.79 it's just Crtl + N and there's no tickbox).

What it looks like is that for whatever reason the scan mesh isn't whole, like there's separate islands of vertices which would give the effect of the cracks