Miniature stone retaining walls are a valuable asset to the outdoor model railroader. They are both functional and good looking. Used properly, they increase a layout’s realism tremendously. But creating a stone wall to fill an irregularly shaped gap can be daunting -- even more so if the wall must be curved.

I’ve come up with an easy way to make scale, stone retaining walls that fit realistically into the rocky terrain of my layout.

I use 3/16” thick foam core art board to make a form for the wall. I begin by cutting a piece to fit the location.

One way to do this is to lay a board across the gap, with 1” or 1/2” increments marked on it. Then measure down at each increment. Then simply transfer these measurements to the foam core and cut it out. It doesn’t have to be perfect.

In some cases, a profile gauge (aka “contour gauge”) can be used to measure the shape of small gaps.

If the wall must be curved, gently crease the foam core and bend it to shape.

Next, use hot glue to attach strips of foam core around the perimeter of the cutout shape. You may need to angle these strips inward along the bottom edges of the form, in order to make the wall fit better into the slope of the terrain.

Next, place small rocks into the form. These can be random shapes, or cut stones. For this wall, I used cut stones along the top, and random stones for the rest of the wall.

Small cut stones can often be found in the tile department of Lowe’s or Home Depot, attached to a flexible backing. In most cases you will need to peel them loose from the backing.

Use thin stones along the lower edges of the form.

Next, cut a piece of 1/4” hardware cloth (wire screen)to fit into the form. Again, this need not be perfect, just a loose, approximate fit. Lay the hardware cloth over the stones, being careful not to move them out of position.

Now mix up some mortar. I like to use a roughly 50/50 combination of Rapid-set “high strength” mortar and vinyl concrete patcher. The darker vinyl cement tones down the whiter mortar for a more realistic appearance.

You’ll want to make the mortar about the consistency of thick pancake batter. Too thin, and it’ll run under the stones, ruining the effect. Pour the mortar into the form, and carefully spread it so that it fills the form out to the edges and just covers the hardware cloth.

At this point, you may wish to gently press some thin stones to the mortar along the top edge of the wall, if that part of the wall will be visible. Doing so will make the wall look like it’s built entirely of stones rather than only on one side.

After the mortar has set, carefully peel back the edges of the form. Then turn it over and let the wall drop out into your hand.

Now test fit the wall on the layout. If necessary, you can gently sand away some of the mortar along the edges to achieve a better fit.

Once you are satisfied with the fit, cement the wall in place. For this I use the high strength mortar with a bit of concrete coloring tints added, to match the color of the surrounding rock.

Push this mortar down around the back of the wall, letting it squeeze out a bit through the gaps. Small stones can be used to fill in any large gaps. Rinse away excess mortar with a hose, using a fine spray setting.

For long walls, you’ll need to work in sections. Here, a small form is being made to fill a gap between two walls.

The completed wall, including a stone bridge.

The bridge was built using the same technique, by cutting an arch into the form. After the bridge wall was in place, another piece of foam core was used to form the underside of the arch. Stones were placed over it, then mortar poured on top.

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