Wednesday, April 18, 2012

Rock Work 101: Part II

Okay, enough theory! Let's carve some rocks!

The formation I'm currently working on is one I call Baxter's Butte, roughly modeled after all the different versions of the Big Thunder spires. When completed it will tower 100 scale feet above the railroad bed and should serve as a striking central scenic feature for the railroad. Follow along with the photo captions  and the video to see how I go about making it.

Here are most of the basic tools and materials I use to make my foreground rock formations. The main ingredient is a polyurethane carving media called Balsa Foam. This stuff comes in different densities but I prefer the soft version for sandstone rock work. I find the 9x12x1" sheets to be most flexible since I like to work on small sections and then build up a formation from several pieces.

The coping saw is used for cutting out basic shapes in the foam and the good old #11 X-Acto knife is the primary carving tool.

The stuff in the caulking gun is Loctite Power Grab all-purpose adhesive, the best thing I have found for sticking foam to foam or to anything else. It grabs hold instantly but still allows a working time of 15 -20 minutes. For laminating two or more slabs together though, I still use yellow carpenter's glue and pile some heavy books on overnight.

This photo illustrates the sectional nature of the butte and also the rock layers that are being simulated. Three, 9x12x1" sheets of Balsa Foam have been used to construct the butte so far and it narrows from a roughly 1" (4 scale feet) thickness at the top to about 5" (20 scale feet) at the base. This was achieved by building downward in sections from the top and adding more laminated slabs for thickness toward the bottom. When completed, the Butte will sit atop a sloping base of polystyrene foam, built up in layers to achieve the desired height. It should be noted the pink polystyrene foam insulation is much less expensive than Balsa Foam which costs about $10 a 9x12" sheet!

My preferred rock carving tool is a #11 X-Acto knife. The good news is that it doesn't need to be particularly sharp so now I have a use for all of those old dull blades I've been saving. Balsa Foam has a texture that is very similar to actual sandstone and it is an absolute pleasure to carve. I usually work on one small area at a time, bringing it to a near state of completion before moving on to the next. There are a few simple techniques and tricks to this that anyone can master. It all starts with a downward carving motion as shown above.

Then I use a side to side scraping motion to create facets in the rock. It's important to remember that sandstone is basically a crystalline structured rock and therefore breaks and splits at right angles. Over time, weathering wears some of these angles smooth and we get the myriad facets of rock that we see throughout canyon country. From a distance, these facets often look like lines, but when carving them you should always try to get a dimensional look where the different facets meet, with one sticking out a little more or a little less than the other. That's what makes the rocks look real.

Cutting and whittling is used to define specific line breaks in the rocks, like where two layers come together. This gives you something to carve down to when creating the rock facets. I always measure and lay these important horizontal lines out in pencil before carving so that they stay uniform throughout. At the same time though, you don't always want these horizontal lines to be perfect. They should be lost and found, broken in places by rock falls or crevices. When carving rocks it's important to remember that you're not making a brick wall, things should look a little chaotic and random. This is Nature after all. It can be a challenge. Humans tend to look for and create patterns and often times I've found that the row of brocken rocks I've just created all look a little too perfectly spaced. If that happens, just break it up some more, remembering to be as random as you can.

A medium sanding block is used to smooth and flatten surfaces, remove large bits of material quickly, and to remove mistakes and prepare an area for re-carving. 

The last tool in the box is spackel. I use it to fill gaps between slabs and to smooth transitions between separate pieces of foam. Woodland Scenics sells a product they call "Foam Putty" to do this very thing. As far as I can tell it is exactly the same stuff as painter's spackling compound except for twice the price. I use Patch N Paint from Home Depot.
Here's a quick video demo showing a little rock carving.


In the next part of this series I'll be showing how I paint the rocks with artists acrylics and prepare to install them on the layout. If you have any questions, just leave them in the comments section or come join the conversation over at

Click here for part III of this series.
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