How to Build an HO Scale Tunnel

Survey your layout--whether it̵7;s still on paper, already under way or now running on plywood--and decide where to locate your tunnel. On a typical HO layout with a loop at each end, a tunnel in one corner is pretty standard. It can hide an unrealistic curve as well as a parked train, and it covers a largely unusable piece of real estate. Whether you choose a corner or somewhere else, avoid enclosing a turnout or leaving trackwork inaccessible.

Mark the start and end points of your tunnel, which is where you̵7;ll install the portals. While you can make your own portals, they̵7;re available in abundant variety, finely detailed and moderately priced at hobby shops or online from manufacturers like Woodland Scenics and Chooch Enterprises. Buying commercially also should ensure proper clearances, whether your portal spans one or two tracks. Attach the portals, perpendicular to the track, with white glue.

Add sidewalls behind the portals, just long enough to act as view blocks. These panels can be fashioned out of anything from card stock or foam core board to commercially available precast wall units. Keep in mind, however, that the walls may have to parallel curved track, so be sure their material has enough flexibility.

Create a reason for the tunnel to exist. Typically that means building a mountain to enclose the trackwork, following any of many time-tested methods. One of the simplest is hard shell, which uses a latticework of cardboard strips covered with newspapers and plaster. Sketch the outline of the mountain̵7;s base directly on the layout, then turn large corrugated boxes into inch-wide cardboard strips, using a utility knife to cut across, not with, the corrugations.

Staple long strips every few inches along the mountain̵7;s outline. These will be the framework̵7;s ribs. Extend them up and over the tracks, adding pieces as needed to extend their length, then staple them once again on the other side of the tracks, either to the benchwork or a backdrop. Next, interweave horizontal cardboard strips, alternately over and under the ribs, stapling or hot gluing each intersection until the latticework is complete.

Cover the framework with newspapers, giving you a rough visual of the mountain. Traditionally, at this point you would soak paper towels in a bucket of plaster and apply them over the newspaper. A cleaner and easier (albeit more expensive) approach available today uses plaster cloth, the kind that immobilizes broken limbs in a cast. Available in rolls from scenery-supply houses, the cloth can be cut into manageable sections, soaked in water and easily applied to your mountain.

Let the plaster cloth dry thoroughly, then brush on a light coat of diluted plaster. After the plaster dries, you̵7;re ready to apply rock molds and other scenery.