Carving Rock Faces - XPS Foam

A quick look at my technique for Carving XPS foam board into rock faces. This was done for the Rockingham Model Railway Group's HO Layout here in Baldivis West Australia. Check out their facebook page.
While there are many techniques for carving and creating rock faces this is the one I used. As usual any feedback would be appreciated.
cheeers I hope you get something from this