I have bench work with a thin layer of perfectly smooth plywood overtop the frame itself, is it better to start modeling over top the plywood or should I have a layer of the insulation foam board over top the plywood before I begin laying my sub-road bed and creating my hills and scenery?
There are lots of threads about this (you can search at the right side of the screen). Generally, it is best ot use at least 1" of extruded foamboard over the plywood. It’s more stable and allows you to adjust terrain down. There are some other advantages too.
Welcome to the forums.
I would suggest a layer of 2" foam before you lay your track. The reason being is that you can have below track level scenery such as rivers, culverts and the like.
I have used cheap latex caulk for foam to plywood, cork to foam and track to cork. A very thin layer is all that is needed. A little weight on top for overnight is a good idea. If you are using flex track, T-pins will help it hold the curve while the caulk sets up, still want the weight on top.
Have fun,
I would use foam on the plywood. On my layout I used one inch thick foam. If you are going to be modeling mountains, two inch foam will allow you to go deeper. However, two inch foam can present a challenge when mounting switch machines but it can be done using the right techniques.
You didn’t say how thick your plywood is. If it’s 1/4" thick, you will want the reinforcement of gluing the foam to the plywood. If it’s 1/2" thick or better and supported, an alternative to foam is to cookie cutter the plywood. This means cutting out the sections of the plywood (usually with a jig saw) where the scenery will be below track level. Raise the remaining plywood above the frame on risers and cleats. The cookie cutter method also gives you a way to vary elevations at different points on the layout by adjusting the risers and cleats. The cookie cutter method can also be used with foam on top of thin plywood.
my thoughts, your choices
Fred W
It depends on what materials and fastening methods you want to use, especially for roadbed and track. Another option is 1/2" Homasote and/or Homabed of different thicknesses over the plywood (good for holding track spikes and nails).
Dante
I use 2 inch foam and have really liked it. Just make sure you don’t lean on it, it will sink in some…
Welcome to the site.
Cuda Ken