Every once in a while some innovative model railroader will come up with an idea, technique, or material that makes modeling a bit easier or more realistic. We can't say who started using styrofoam plastic for model railroad baseboards, but the first time we saw it was on Jim Shiff's N scale open pit mining layout; the same layout featured in the Summer 1971 issue of 1001 Model Railroad Ideas. Modelers have used the material for scenery and for insulation since it was first introduced but never for a complete baseboard. Jim's " secret," to our eyes, was that he had discovered a type of styrofoam that was far finer than the type that is used for packing Japanese radios and the like. The material Jim found is actually called Urethane foam and it is similar to the material used by florists but far harder. If you live in a major city you may b e able to find a supplier under the telephone book's yellow page heading "Plastic, Foam." We also found that several building supply firms and lumberyards carried a new roof insulation material that is almost the same. The "stuff" you want has the density of the florists material but is about as hard as the common white packing material. We've seen it in white, a marbled biege, and green but the color is not important since you'll want to paint it anyway the stuff will literally powder off in your hand if you don't seal the surface with a coat of paint.
The best application we've found for the material is for the small shelf type of layout like an industrial or freight yard. You can obtain the Urethane foam in several thicknesses; the most common and useful one is about two-inches. This material is self-supporting for a span of about two-feet. A lightweight framework of 1x2 lumber is enough to support chunks of the material up to 4x8-feet. The material has very little holding power - if you hand-spike your rail to individual wood ties, stick to the proven materials for baseboards; the cardboard like Homosote or Upsom board wallboards. The Urethane foam is only use ful for those who use sectional or flexible track with plastic ties already "spiked" to the rails. Even with these types of track we'd recommend that you hold the track in place with at least one-inch nails or s traight pins. The main reason we like the material is that it is so easy to "sink" the ties into it up to the level of the bottom of the rails. Most railroad yard and industrial trackage, and the majority of the track on some branchlines, has been used so long or was laid right on the ground so that the ties have all but disappeared from sight leaving only the rail and a dim outline of the ties showing above the ground. With a conventional typ e of baseboard the "ground" must be built up to the level of the rail's base web with sheets of cardboard or a layer of plaster - both difficult and time-consuming operations. With the Urethane foam all you have to do is mark out the location of the track, remove the track, and rub away the powdery foam material with a hard typewriter eraser until enough has been removed to allow the track to "sink" into the baseboard up to the rails. If you do decide to use the Urethane foam for the baseboard, we'd recommend that you use this method of "sinking" the track for its greater realism and, more importantly, because the depressed "troughs" you make for the ties will hold the track in place far better than spikes could.
The track is held in place, temporarily, with common straight pins or similar-size and length nails. When the final position has been determined the edges of the ties are marked off and the foam below them rubbed away into powder with a rough eraser. A mixture of plain Latex wall paint is used, along with an abrasive-type filler sold by better paint stores to give a rough texture to floors and boat decks, in a mix that is simply brushed into the troughs where the track will lay. The track is replaced while the Latex paint and texturizer mix is still wet. The mix acts as both simulated ballast and glue to hold the track in place. If you want even more ballast you can mix equal parts 6f powdered glue and scale ballast like that sold under the Campbell and B&H labels. Pour the mix onto the track and distribute it exactly where you want it with a fine brush. Then spray on a fine mist of water and a few drops of detergent from a Windex type spray bottle. Be sure to keep the ballast and glue mix away from the points and other working parts of any switches.
The one-inch thick sheets of Urethane foam can be bent enough to be used as baseboard for the hillclimbing grades of a mountain-type model railroad if the material is glued and nailed securely in place. A plain knife is all that is needed to cut the material into straight strips and curves to match your track plan. The only reason why Urethane would be used for this type of construction, though, is to save weight on a portable lay out or on a very small N scale layout; Homosote or Upsom board would, again, be best for the "country" and mountain portions of most miniature railroads. Use the Urethane for the yard and industrial areas or for the smaller portable railroads.