The use of extruded foam on top of modules is now very popular. Many N-Trak modules have a sheet of ½” or ¾” foam glued to the ½” plywood module top allowing for landscape contours below the track grade. Extruded foam is fairly rigid and, if accidental compressed, it will not rebound to its previous shape. Accidental compression of the foam is generally not a problem, since true ground areas are rarely flat anyway.

However, foam compression can become a problem when it occurs under the area where the rail joiner tracks are installed. Without firm, flat support underneath them, the joiner tracks can sag as trains pass over them, thereby causing uncoupling, derailment or other problems. Some module builders place a 2’ long piece of 1” x 4” hardwood flat along each end of the module to protect an area 3½” in from each side and which fits flush with the ¾” thick foam that covers the rest of the module. Unfortunately, wood and extruded foam have different coefficients of expansion and therefore, over time, cracks appear in the module’s ground cover along the seam between wood and foam. (Figure 1)

You can solve this cracking problem and provide adequate support beneath the joiner track area by still using a piece of 1” x 4” hardwood, but making it only 4” long and rotating it 90°. Cover the entire module top with foam, then center the 4” long piece of wood under the yellow (middle) line at each end of the module. (Figure 2) Since dimensional lumber 1” x 4”s are actually ¾” thick and 3½” wide, this placement will make the piece of wood extend forward and back 1¾” from the center of the yellow line, which is sufficient to underlie both the red (front) line and the blue (rear) line. (Figure 3) With a sharp knife, cut the foam along the edges of the lumber, remove the cut block of foam, (Figure 4) and glue and screw the piece of wood in its place. (Figure 5 & 6) Obviously, if your foam is of a different thickness than ¾” you will need to use an equivalently thick piece of wood. (Figure 7)