Modelers have been using solid spline roadbed for years on their layouts, particularly indoors. I used splines cut from redwood bender board on my previous outdoor large scale layout in California back in the early 90’s. But here’s a new twist on splines that may interest some of you, especially if you live in a damp climate where wood tends to rot quickly or where termites can be an issue.
Until recently, I had been using lightweight PVC lattice roadbed on my layout here in Oklahoma. I am installing some new track work and wanted something a bit stronger for this section. I decided to go back to spline roadbed, but made with plastic rather than wood. The spline roadbed provides extra support for the large number of curved turnouts on the new section. It helps to ruggedize the portion of the layout that I expect to be most heavily utilized and most prone to accidental “step-ons” by busy operators.
I am using 12 foot long 1” x 2” Cellular Vinyl PVC boards -actual size is ⅝” x 1½” - for the splines. The brand was Royal Mouldings™ Trimplank® Premium NeverRot® Moulding & Trim. It is sold at many of the “big-box” home improvement stores and at some lumberyards. This material is perfect for outdoor use. It is waterproof, insect-proof, and maintenance-free. The following photo shows a few of the PVC boards lying on a pair of sawhorses.
Unlike Trex® or other composite decking materials, cellular vinyl PVC is 100% plastic. It contains no sawdust or wood fibers. It cuts, drills, and holds screws just like wood without any of the shortcomings. It does not warp or deteriorate and has a lifetime warranty. There is a disclaimer in the warranty that states “exposure to temperatures in excess of 145˚F may cause some expansion and contraction.” Although it does get pretty warm here in Oklahoma, if it gets that hot I won’t be outside to notice it.
My finished roadbed is 3⅛” wide by 1½” thick. It consists of five individual splines that are assembled with construction screws into manageable sized sections. The screws are driven from alternate sides at approximate 6” intervals. These 12 foot long sections are then bolted together with four 3½” x ¼”-20 carriage bolts through “finger joints” at each end. The splines are quite flexible before being screwed together and can be formed to any desired curvature. They become very rigid when screwed together. The following photo shows me holding a 12 foot long section with a large diameter curve leading into a curved turnout. This same section can be seen at the top right of a subsequent photo lying on the block wall before it was installed.
The PVC boards are white but I spray them with brown paint so that the white will not show through any thin spots in the ballast. In the following photo portions of the roadbed had not yet been painted and you can see where the “finger-joints” between the sections are bolted together. You can also easily see how I interleave the individual splines at turnout locations.
The following two photos show how I use templates to build the roadbed sections that go under turnouts to ensure that the roadbed matches the turnout geometry. They also give you close-up detailed views of how a “finger joint” goes together and how splines are interleaved at a turnout. This particular joint was on a 30 foot diameter curve between two curved turnouts. The paper template for the turnout was placed on a piece of particle board and 2” finish nails were driven in along the outer edges of the splines to hold them in place while they were screwed together.
During construction, the PVC roadbed is temporarily supported with pieces of wood and/or bricks and held in place with grade stakes. After final leveling and alignment, decomposed granite is used to fill-in along and under the PVC roadbed. The roadbed “floats” on this granite fill material.
I spaced the yard tracks at 9 inches on centers to provide a bit of extra room to reach in for uncoupling. The extra space also allows placing a foot between the tracks if needed for maintenance or to access a wayward piece of equipment. Storage tracks and mainline sidings are spaced a bit closer at 7 inches on centers. I’ll take some more photos after the decomposed granite fill is added and after the track is down.
More to come later,
Bob