1/4 inch ply under foam insulation board, n scale...doable? - Model Railroader Magazine

Hello All,

DonRicardo

...but will use 1" foam glued on top of a second 1" foam and sandwich the wiring between the two layers...(Underline added for emphasis.)

That's a really bad idea!

PennCentral99

I don't like that idea. You need to keep your wiring accessible. Digging for it while buried in foam is not good or fun.

I completely agree.

A primary reason for using foam as a base is the ability to carve or sculpt terrain features into the foam.

I wouldn't want to breach a feeder wire sandwiched between two pieces of foam for fear of fire.

Think "Call Before You Dig" from prototypical utility companies.

On my 4'x8' pike I have no underneath access, it sits on the spare bed in the computer/railroad/spare bedroom.

Originally, the base was 1/2-inch Medium Density Fiber Board covered with 1-inch foam.

I used 2-1/2-inch Luan plywood strips; like a facia extending up from the edge of the MDFB, for stiffening.

The MDFB was heavy and prone to sag, even with the stiffening stringers.

To upgrade the base I made an open grid 4'x8' frame of 1"x4"s with stringers on 32"x24" with 1/4-inch plywood under the 1-inch foam to replace the MDFB.

This is much lighter and stronger with limited under-pike access.

For my wiring, I cut straight "utility trenches" in the foam; 1/2-inch deep and 1/2-inch wide using a 1/2-inch wide wood chisel.

I used 1/2-inch Split Poly Loom; used for automotive wiring harnesses, press fit into the "utility trenches." 

This allowed me to paint, scenic, and ballast over the wiring while still allowing access.

When I needed to make direction changes (junctions) I used a 2-inch hole saw and cut "utility pits" in the foam, by hand.

These are covered with small buildings- -for access.

Using this method I was able to run track feeder wires in separate "utility tunnels" from turnout control, by creating parallel paths.

All these "utility tunnels" converged in a 9"X16" central "utility pit" which holds the terminal strips, Auto Reversing unit, and circuit breakers.

From the central "utility pit" to the control panel I cut five (5) "utility tunnels." These pass directly under three (3) lines of ballasted track.

Hope this helps.