Making and painting styrofoam hills/mountains

I paint directly on the foam using latex paint. Then stages of dirt, leaf litter, ground foam and static grasses. By the time you cover it with all of this stuff, the foam and paint will be mostly covered anyway. Trees plant nicely in the foam. All of my scenery lifts out in sections.

The second photo shows using plaster for rocks. The tunnel has a primer coat.

In the '80s, before hot wire cutters, or at least before I knew of them, I would use lacquer thinner on pink styrofoam.  Depending on how much you brush on, the melting styrofoam takes on a somewhat of a rockery shape.

Then I would use acrylic paints and the usual commercially available ground covers.  Finally, Yarrow picked from fields was used as trees.  The Yarrow dries hard and is easily flocked.   

I was in my 30s and probably should not have used this method, but I'm still here.  Of course the cellar doors were kept open.  I may be dumb but not stupid.....LOL

There are a slew of YouTube videos on this subject but as Christopher posted, you can just paint the Styrofoam.

-Greg

This is all blue or pink styrofoam board, carved with Hot wire foam factory tools, interior latex house paint, Scenic Express texture and vegetation. The flat level surfaces have Fusion Fiber on them.   No plaster !!  I tried plaster a long time ago and never do that again.

I don't know why my rails are red in this photo, because they are not 

As Dan alludes to, be careful!  Water-based latex paint might be ok, but I know for a fact that some spray paints will absolutely dissolve some types of styrofoam.  I've even seen where the black "rubber" of a model vehicle's tires ate into the foam after a few months. 

Does this type of foam have a generic name?  How sure are you that your foam has the same composition as what's illustrated above?

Before you go wild on the layout, I would try a little bit in a well-ventilated area, and wait a few days to observe the effects.  My $.02.