Today I did a test of the stone walls of the attic. I just did a small piece as a test. I want to make sure it looks good, and doesn't take too long to finish before I start the final set. I went to Lowes and got a couple sheets of this blue insulating styrofoam. It's pretty inexpensive and perfect for this application.
I drew the rock outlines onto the foam, and I used this woodburning tool to melt the foam where the mortar would be. *WARNING* If you choose to do this, do it OUTSIDE while wearing a respirator or a mask. The fumes are poisonous!!!
After I melted out the areas between the stones, I lightly and repeatedly dropped chains on the foam to create intentions and textures in the stones. I then painted the whole thing light gray. I brushed acrylic paint for this. DO NOT USE spraypaint. It will melt the foam and create poison gas.
After the gray paint dried, I painted just the stones a dark gray (mix black, white, paynes gray)
I then roughly painted them a slightly lighter gray letting the dark show through. Then, to bring out the details, I lightly drybrushed white on the stones.
I then used an airbrush and from an angle hit it with black. This helped to create depth. I finished it with some moss and mold. I used much more mold than I will use on the actual set. For this I used scenic grass that's made for toy trains. I'm pretty happy with the way this looks, and I will start the actual set on Monday.