Ballast: How to lay rock so your model trains will roll
 

Like a fine paint job on a locomotive, ballast is the finish coat on your track. It covers the many blemishes of roadbed construction, such as joints, shims, screws, and wire holes. More importantly, if done properly ballast adds a lot of polish to a layout.

Ballasting is usually the last finish work I do on any given section of the railroad. I like to at least add the basic scenery adjacent to the track to be ballasted, as there’s nothing worse than dropping a glob of white scenery plaster or paint on track once it’s ballasted. My layout happens to be HO scale, but these ideas apply regardless of scale.

 Preparation

The first step is to establish a ballast profile foundation. This will vary with the type of track: main line, branch line, or spur. Spurs and sidings typically have lower profiles. Such cross sections vary with the railroad and the period of the prototype.

Ballast slopes can be shaped using plaster, Styrofoam, or a filler material like sand to augment the slope of the wood, cork, or Homasote roadbed base. Glue filler materials in place as necessary.

In general you want to avoid the trap of 45-degree jigsaw cuts and sharp edges and create a natural angle of repose for the ballast material. The steepest slope should be no greater than 1.5-inch of horizontal run for each 1-inch drop—in other words a 1.5:1 slope. Slopes of 3:1 and 4:1 are not uncommon.

Get rid of any sharp edges on the roadbed—such as the jagged corner on cork—and remove any little bumps of plaster along the right-of-way. They tend to stick up through the ballast. While you're shaping the ballast profile you can also make drainage ditches, although those should be allowed for when you design your overall scenic plan.

 
Painting the base and track

When you're happy with the right-of-way profile, airbrush the track and roadbed a flat base color. I like to mask areas such as switchpoints and paint those by hand. I use a dark brown such as Floquil Roof Brown, but other colors may be more appropriate to your locale. This paint takes the gloss off of plastic ties, colors the rails, and blends in any filler materials. Clean off the tops of the rails as soon as you finish painting.

 Ballast material

I use rednip ballast top up with fire ash and coaldust in order to acheive that authentic look. All loose ballast is slightly dusty but this will dissapear once the glue stage is complete

Securing ballast

Once the loose ballast is positioned, you can begin to wet the ballast. I use water with a couple of drops of dishwashing detergent in a hairspray bottle, which provides a very fine mist compared to most other pump spray bottles.

Initially point the sprayer up and let the water cloud gently fall on the ballast. This light mist tends to keep the ballast from being blown around. Once the surface is slightly moist you can be more direct with the spray. Use enough water so that it soaks deep into the ballast. If only the surface is wet, then the adhesive won't soak in and the result will be a loose, crumbly crust. If a detergent bubble forms in the ballast while spraying, creating a mound, burst the bubble and soak the spot. If a little ballast gets out of place, you can generally nudge it back, but be careful.

Once the ballast is soaked, dribble on a 50/50 mixture of white glue and water mix . An old glue bottle to apply the mix will do, and is less tedious than an eye dropper. As long as the ballast is well soaked, the glue mix will spread throughout. If the underlying ballast isn’t thoroughly wet, the adhesive mixture may float some of the ballast. Spray some water on the spot to correct this.

Precautions and final touches

The glue can lock switch points into place, so to prevent this, apply light plastic-compatible oil to the ties under the points. As the glue sets, move the points back and forth to free them. Keep the ballast in the point area at a minimum, well below the tie tops.

Once the adhesive sets, but before it's completely dry, knock off any stray pieces of ballast that have adhered to the rail sides or tie tops. In high humidity it may take a couple of days for the glue to completely set. I find that ballast is darker after it has been glued.

As a final touch, lightly overspray the track structure with thinned roof brown or another appropriate color to slightly weather the right-of-way. Not only does this represent dirt and wear and tear from passing trains, but it also cuts some of the stark contrasts present on newly ballasted track.

With a bit of care, ballasting can transform toy-like track into a realistic scale model.