Polystyrene, cement, stone sculpture

Tools

hot wire for big chunks, sturdy soldering iron, small blow torch with small gas cylinder (as used by bush walkers) gas mask, 

Safety hints

Make sure there is cross ventilation, and you are working in an open area with at least two openings instead of walls, wear safety gas mask because gases will be given off when using hotwire and flames, that may cause you alergic reactions,.

How to sculpt

If you use a hot wire, take off the bulk of the unwanted areas, binning the residue.  If you use a saw, watch for flying debris that may be breathed in by  you, a pet, and cause lung dramas.

With the soldering iron, goudge into the mass, taking more definite bulk from areas that you want to be spaces.  

With the flame, approach your target spot, slowly, from a metre away.  Slowly move flame over surfaces, not lingering for long or you may set the whole thing on fire that continues to keep burning long after you stop.  Melted polystyrene effects can be beautiful.  Experiment to find, then use, the effects you desire.  It stops the sculpture looking like polystyrene, smoothes out edges into more rounded forms.

Finishing touches

Using Zinsser primer, sealer, undercoat, cover the whole surface.  When dry, the surface will accept your acrylic paint, modelling texture and paper mache (for adding mass where you want it.  E.g. when I burn too much, I need to restore the form by modelling).  I use Bondcrete for the glue, undiluted, because it is weatherproof and very strong.