Modeling Rocks

The rocks made here are shown being added to the scenic base of our diorama built in the previous article but they can be applied over any type of scenic base or put to use on any layout.

Rock from Ceiling Tile

There are many ways of recreating rocks, which is good because in nature there is endless variety. An easy way to get started, which requires absolutely no artistic talent or deep pockets, is broken ceiling tile. These fiberboard tiles are common in drop ceilings. They are easy to cut and easy to break. When snapped, the broken edges take on a stratified, rocky appearance. The 1/2 inch tiles can be used individually or stacked to create taller walls. These rocks work very well in cuts around railroad tracks and roads.

tile rocks

A ceiling tile can yield hundreds of rocks for a model railroad. Even a broken or discarded tile can be recycled for your scenery.

To make rocks,

  1. Snap the tiles. The closer you hold the tile to the breaking point, the tighter the grain of the rock will be.
  2. Trim the rocks to fit the space available using a sharp utility knife.
  3. Stack and glue the tiles using carpenters glue (a hot glue gun will also work on the tiles for faster set-up time.)
  4. Blend the rocks into the surrounding scenery.
  5. Add color, depth and highlights.
Rock Cut

After trimming the rocks to size, stack and glue to create the cut.

Sound easy? It is. It’s also easy to experiment. Try different arrangements, stacking tiles on an angle, and different combinations until you like what you’ve got. Small track nails or pins can be used to hold rocks in place while glue dries. Once the rocks are glued together, it is time to tie everything together. To do that, we’ll apply a thin hard shell to the scenery at large, sculpting a few more rocks of our own along the way.

Hard Shell Made Easy

Stiff hard coat

Start with a thick mixture of plaster. This can be worked into many gaps or piles to create new rock. There will be plenty of time to sculp while it sets.

“Hardshell” scenery is one of the oldest methods in the hobby. It is often used over a frame of screen wire, newspaper or cardboard. Our foam base is plenty strong without the shell, but this plaster coating will cover some blemishes and add detail. The shell is made from drywall mud. Use the dry mix, as we’ll need different consistencies for different parts of this project.

First, we’ll start with a stiff mixture that will allow us to sculp additional rock details. Mix the mud in a small container, adding water to the dry plaster. You can also add a little gray or black acrylic paint or dry pigment to the mix. This will help add just a touch of color and prevent a stark white spot if the plaster ever chips down the road. This mixture should be about the consistency of peanut butter, with no lumps.

Wet hard coat

A cheap foam brush makes a great applicator for the wet coat. This is a great way to add texture to rocks carved in the foam.

Place the plaster wherever you want to make rocks. You can also use this batch to fill in gaps or smooth transitions between foam layers. As the plaster starts to set, it can be shaped with putty knives or other flat implements. The drywall mix will give you a long set-up time to work with, and the thicker you put it on the longer it takes to dry. You can continue to carve and detail the rock even after it has set.

Next we’ll mix a very watery batch of plaster to seal the tile rocks created earlier along with some of the other porous foam areas like the sides of the fill. Mix this batch the same way, adding water to the plaster until it gets to a very smooth, wet consistence without any lumps. You should be able to apply this mix with a brush or sponge. You can spread this across all of the scenery. If nothing else, it eliminates the sea of pink. Work it around the tile rocks to help seal everything. When you’re finished, the rocks should look like they are buried in, not sitting on top of the surrounding terrain.



After several washes of paint, the rocks and terrain begin to take on a realistic tone.

Allow the plaster to dry completely before beginning to add color. This may take 24 hours. You can use either acrylic or oil-based paints on the plaster, but it is safest to use acrylics since oils will attack the foam. Thin all of the paints so that they can be applied in washes. To make colors stronger, repeat washes. Don’t try to achieve your final results in one coat.

Begin with a gray or brown base color. This can be applied over everything. You can mix colors as well. Tinting different layers of the rock strata in cuts is a realistic way to add detail. You can further vary the colors by applying additional washes to specific areas.

finished rock

After all the washes and highlights, the rock cut has taken on added dimension.

After the basic color(s) have dried, apply a thin wash of black to the rocks. Allow the paint to settle into all the cracks and crevices. This will add depth.

Lastly, highlight the ridges by drybrushing white paint, or using white chalk on the high-points of the rocks. Drybrushing is a technique where a little paint in placed on the tip of a brush. Most of the paint is then wiped off. Whisking the brush across the ridges will then transfer only the remaining residue onto the surface. The contrast between black, base color and white adds a surprising amount of depth and detail to both the tile and carved plaster rock.

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