Also, in addition to adding burnt umber to the mix I add small rocks, forest debris, tree leaves, oregano, sticks and sand into the Sculptamold. This gives you some nice embedded earthy litter into the ground. It really adds a lot of nice texture especially if you have a tree root or two sticking out.
Another cool thing is when the Sculptamold mix has been applied to the base and is about two-thirds dry if you take an X-acto and start picking holes into the hard crust you can create really distressed looking ground and with the added litter materials really looks like a churned up battlefield.