Cutting and shaping Styrofoam.

There is one other method that I experimented with a few years ago - you can "etch" the styrofoam into shape using straight laquer thinner in your airbrush.  I was cleaning enamel paint out of my airbrush and sprayed the laquor thinner on some white styrofoam that was sitting around to see if it was clean.  I guess if you dilute it with some water it will melt the foam into hills, bumps etc. but can be hard to control which seems to give a more life-like product. Pools of thinner make great bomb craters. Haven't found the perfect way of doing it yet, but have dicovered that the "small balled" styrofoam can be carved into finer detail than the courser stuff.  Just spray it on thin, let it work and then reapply as necessary. Doesn't take long - the thinner stops eating the foam after a few seconds.  After it has cured, apply spackle and your groundwork.  Sorry, don't have any photos of a finished product, just enjoyed an afternoon of melting down a large stack of styrofoam!

There are basically two ways to shape styrofoam, hot or cold. Hot uses a hot-wire cutter and / or a hot knife, both available from online shops like Micromark or also found in craft stores. A hot-wire cutter is just as the name sounds, it is a hot wire that is mounted to a handle which melts through the foam, a hot knife, ditto. The main problem with these is the smoke, which is noxious. Good ventilation is a must. I don't use these.

Cold cutting styrofoam is a messy job. It is statically charged and flies all over your work area. Big clean-up. Outside of the normal X-Acto knives, razor saws, gouges and other implements of destruction, my tools of choice are riffler files. These are curved jewelers files with coarse teeth that come in a variety of shapes, very useful for carving things like foam. Keep the shop vacuum handy, you'll need it.

Dremel tools with cutting burrs can also be used, but this really makes a mess, foam bits will be flying everywhere!

Keep in mind that the foam only provides the basic shape. Once you cover it with the plaster bandage, most features are smoothed over. You don't have to cover the whole area with plaster bandage either. Sometimes I leave areas in raw foam, just to cover them with a thin layer of plaster. Other times I cast rock outcrops from latex molds and implant these into the foam, spreading plaster around them to blend them in, but leaving the cast rock texture exposed. Here is an example;

You need to decide ahead of time where you want certain features and be able to add these to the wet plaster as you work. Tire ruts, foot prints, shell craters, etc., need to be planned out carefully, as you don't have a lot of work time. You can also work in separate, small areas, blending each area into the next, so that you don't have to do all the work at once.

Assemble a collection of plaster-working tools. Spatulas, pottery-making tools, old coarse-haired brushes and my favorite, a tree branch with a rough, jagged, broken end, useful for poking texture into places where there is none.