I am planning to build a HO layout that is 5' x 12' that is built with 1x4 pine framing with crossmembers. I have looked at various sites and videos and I would like to find out what are the pros and cons as to using just 2" foam on the framework or using 1/4 plywood with the 2" foam on top?
Pros of using foam: easier to form "topography" on the layout; also helps to deaden noise.
Putting the 2" foam on top of 1/4" plywood makes it easier to mount 'Tortoise' under table switch machines, if you decide to use them.
Len
using plywood under the foam protects the foam from damage. if something heavy is dropped on the foam, it won't fracture all the way through.
as a side note to les's response regarding the under table switch motors like tortoise, do not use 2" foam base on your plywood if you use these motors. they are designed with throw rods to reach through about 1" of baseboard. if your base is thicker than that, the rods will flex instead of moving the points.
Plywood gives you something solid to screw through, into your wooden frame, and tying everything together nice and stable. The plywood also allows you to secure things from underneath if you so desire, like wiring, using staples or light wire staples into the plywood and with the foam on top, you don't have to worry about the points coming through and damaging or interfering with anything.
Thanks for everyones input. I did not even think about attaching wires underneath such as for the bus cables and the possibility of something breaking through the foam. I will be going with the 1/4" plywood and the 2" foam. In my area I can only find tongue and groove pink board. Is there a part number for the 2" foam that is not tongue and groove and who makes it?
I have never seen foam above 1 inch thickness that doesn't have some sort of tongue & groove or lap-joint shaped into the side of it.
Sid
Forgot to mention, if you use the Tortoise machines with 2" foam on 1/4" plywood the throw rod has to be replaced with wire that's a bit thicker that doesn't flex as much. K&S has 4 packs of music wire that are handy for this, or you can get 36" pieces. You'll need a hard wire cutting tool though, like the one Xuron makes, because music wire will tear up a regular wire cutter.
Len
If you don't have a hard-wire cutter, a Dremel with the cutoff disk will do just fine.