Styrofoam Rocks

I've had several people ask how I made the rocks on my On30 modules. It was amazing to me just how easy it is to create rocks from blue Styrofoam. This is a HIDI (How I Did It) and not a DIY, since I am making this stuff up as I go!

I used the blue Styrofoam that I picked up at my local hardware store, Lowes. Here in South Carolina all I could find was 3/4" sheet. I just consider it as rock layers. You can always fill in the joints with spackle.

Here I have some scrap Styrofoam and plywood, which I will use to demonstrate my method. Note that I deliberately glued the different layers of foam to create a stepped set of layers or strata, making use of the 3/4" thickness of the foam. In other words, instead of trying to hide the layers the Styrofoam creates, I deliberately enhanced it.

First, glue the Styrofoam sheets together which I used Liquid Nails Panel & Foam Adhesive. When using an adhesive on foam, be sure to read the label as some adhesives can melt the foam. While you can use white or yellow glue, they may not set up all the way as they need air to do so.

Once the glue has set, I used a pocket knife to gouge the foam. Stick the blade in and pry up. Foam will fracture and pop out leaving a random texture.  

Use your thumb and fingers. Pry, claw, scratch, twist, poke, or prod to shape the foam.

As you can see, the foam cuts easily. You can use a knife on the foam but remember to create texture even while cutting; slice in and twist the blade. You want it to fracture and not be a clean cut.

I had a sheet-rock saw handy which I sliced off a corner. Yea, nice rough texture there!

I dragged the saw down and across the surface to rip and tear at the material as I continue to shape the foam.

As you can see, adding texture and rock cuts are just that easy.

Now is probably a good time to step back and look at your creation. The foam is really starting to take shape however, the top is a little too nice for my taste so I will continue to shape the rock formations.

This time I scraped the foam with the blade of my knife held vertically to the surface. This causes the blade to jump and vibrate creating more texture. 

Continued with the blade held vertically to the surface, scraping until you like what you see. 

The point I want to make here is that you can use any tool you have at hand including your hands to shape your foam. There’s really no wrong way, well, maybe using the wrong power tool might be a problem.

Now that I’m happy with my results, I will stop shaping the foam.

Touch Up

For some joints or cracks I would like to fill so I use Spackle to fill or fix the problem spots. The Spackle also helps soften some on the sharp edges from when you attacked the foam. Rock that has been freshly fractured will probably have sharp edges however, after a few thousand years of exposure to the elements it will soften somewhat.

We'll take a break to let the Spackle set up.

Scenery

Dave Frary has instructions on using his rock molds. Using Your Blue Ribbon Rock Molds, I use a different process then Dave does but followed his recipe for making up a basic earth color. You mix 1/3 of your latex paint and the rest water. For paint I just used the cheapest flat latex mixed up at Lowes. I picked out what looked like a yellowish, tarnish color. You don’t have to be exact, just don't make it too dark. We will darken it as we go. Let this dry before the next step.

Next wanted to add some color. I used a tea strainer to sift powdered brown tempera paint over the surface. This is just a random sifting.

Spraying with water, wash the tempera into the cracks and crevices. As you become familiar with the technique you will notice you can control the effect. Do this until you are happy with the result.

Here it is after it has dried. Note that the color will lighten some when dry. The effect is like throwing paint on a canvas, the results are random which is what you are trying to achieve since nature is random.

Next I sprayed on some AI wash. Your layout sits in a room that even with bright lights is immensely dimmer then natural light. That means that we have to create shadows that would appear outside with pigments.

Once that dried, I brushed water across the flat surfaces where I wanted to add zip texture and then zip textured (sprinkled on) a 'brown dirt' (see the Sep-Oct issue of Model Railroad Hobbyist). Zip texture is a mixture of plaster and powdered tempera. By sprinkling it onto a wet surface the plaster will set up and you get this hard surface that is colored. The results are great.

As you can see, once dry, color becomes lighter. The zip texture really adds a lot and looks much more like dirt then almost anything else (except the real thing).

Finally we add rubble.

I bought a 10lb bag of floor sweep at the auto store. Floor sweep is used to soak up spills at a garage and is just clay. I used one of those wire mesh strainers you put in your sink to separate the larger clay bits from the smaller. I put the larger bits down as a base then sifted the smaller material on top and secured with scenic cement. You could leave as is, but I would come back with some more zip texturing using the brush technique: load a brush with the tempera 'dirt', wet the surface where you want it to stick and gently the brush against your finger. You can get really good control doing that.

Of course you can now add static grass, ground foam, bushes and trees.

One last thing. We added shadow by spraying on an AI wash. We also need to add highlights. Take your base color and add some white paint to it then drybrush that across the areas that would naturally have highlights. Let that dry and then take some pure white paint and very lightly, drybrush across the extreme edges.

This is a really easy way to create realistic rock formations with little cost. Try it and let us know how it came out.