Hexa Mesh Surface Detection
 

How do I quickly find the surface cell faces of an unstructured hexa mesh ? By the time of writing I have 4 nested loops:

ic= 1...ncells

jc= ic+1...ncells

iface= 1...6

jface= 1...6

{

vertex comparison of iface an jface to exclude iface and jface from the surface

}

it takes minutes for a 50000 cell mesh on an AMD@1GHz !

Please help, thanks in advance