[Gmsh] prisms and internal surfaces

[Julian Dean]

To any one who can help,

I am trying to creating a specific automated model using qhull and gmsh. First i do a break a cube up into "grains" (volumes) and then i mesh them using gmsh. These grains share internal surfaces and all is good. 

I would now like to expand the model so the internal surface between these volumes is pulled appart (grain boundary) and a layer of prism inserted. Any idea if gmsh can do this and how. Is there a method of extruding an internal surface outwards? At the moment i'm trying to convert the model manually which is tricky keeping track of all the nodes!!

Best regards

Julian