Further Explorations in Making Foam Rocks

I was so intrigued with Ed Traxler’s foam rock construction article I began to hack and slash away at foam blocks looking for something that might fit in with my Arizona based railroad setting. First effort produced spectacular soaring cliffs that will be installed in an appropriate spot at a later date. I was amazed at how easy it was to obtain really nice results and named the cliffs “Traxler Bluffs” in honor of Ed’s technique. Still, I needed other rocks that weren’t quite so ragged and sharp edged. Older, smoother specimens exposed to water and wind erosion.

In a sort of coalescing of “hints and tips”, the “Ties that bind” article I wrote recently featured a stretch of track that immediately found a spot on the layout isolated by a baranca or desert gulch. I have natural rocks that fill the bill, mostly, but needed a few more to pile into the creek and on the surrounding banks. I wondered if a smoother rock from foam was possible and if it was practical to match the coloration of the “real” rock already in place.

I started by using 60 grit sandpaper on a small block of blue foam and sanded/carved a sort of rock like shape into it. Didn’t look like a rock. I threw it into the trash box under the layout.  But I had another idea and grabbed another block of foam.  I chipped away at it with my thumb nail much like Ed suggested in the first place. When I had it all shaped the way I liked, THEN I took the 60 grit paper to it. It worked!!  When it was rough shaped to my liking I grabbed some 220 grit sandpaper and smoothed things out making sure I had taken all the really sharp edges off and smoothed out the ragged surfaces left where the foam had broken when I snapped off the pieces with my fingernails.

Lastly, I used acrylic paints to color the foam. Use a real rock or photos to determine the proper colors. I also used powdered chalks to add color and texture. There is no reason to repeat those techniques here; they are all over the internet and other model building media.

The three basic stages of rock “construction”. From left to right, finger nail chipping, sanding and painting/texturing.

I had one rock I needed to custom fit in a specific location.  In this case I had to laminate two sheets of foam together to get the proper thickness.  I used hot glue (cool). If this is required, when you get the rock fully shaped and sanded, you’ll need to fill it all around the seam with putty of some sort. I use dry wall compound (all purpose) but plaster of Paris will work as well as hydrocal.  Maybe a paper based material like Sculptamold would also work. The plaster based products absorb the paint about like the foam does and so doesn’t cause a distracting mark if the paint wouldn’t absorb. In the picture you are staring directly at the glue line. It runs vertically through the model but is impossible to see

This custom fit rock is 2” thick (or wide). It was laminated from 2 pieces of blue foam and finished with acrylic paint and texture paint techniques using chalk dust.

Try this, you may never again spend time hunched over, scouring a desert for rocks to fit that perfect spot on your layout, only to look up clutching your bag of boulders, to answer the 5 year old who appeared out of nowhere, “Whatch yer doin’ mister?

The new foam rocks in their places.  This is the extreme railroad East end of the Tonopah Southern.  It is the first place to be sceniced and is the default experimental scenery area on my layout.  It is, of course, unfinished but beginning to come together.  The "rocks" fell right into their slots and it is now difficult to tell them from the "real" ones. 

Warning

Sanding blue foam creates very fine particles that cling to everything including your lungs. Wear protective breathing devices. It also sticks to your clothes, fingers, shoes, hair, arm pits and anything else it can get to. Work over an empty box or trash container and use a vacuum cleaner to remove residue from your local work area as well as yourself. It may prevent a domestic disturbance.