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Why Add Foam Insulation on Top of Plywood?
Roger models in N scale and asks:
“I am going to use cork under my track, but have noticed that foam insulation is commonly added on top of the plywood base. I know it adds some height but why not just place the scenery/landscape directly on top of the plywood? Why not just attach (glue or nails is a whole different topic ) the track and landscape directly to the plywood? What’s the advantage of adding the layer of insulation?”
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The reason for the foam is primarily sound deadening. It also makes scenery easier to do (think a gully or creek). Cork on plywood can work but the foam is better.
On my N scale I only used plywood that I had cut into3.5″ straps for the framing and just used 1/2″ foam on top. The way I can cut into the foam to go below track level. I use caulk to hold the track down. I use Kato Unitrack.
The answer is sound deadening. If you nail or glue track to cork to plywood it becomes one solid piece and the plywood amplifies the sound of the engines and cars rolling. Foam provides sound insulation. A second benefit is that foam allows for the scenic carving of the “land”.
It’s really up to you if you want to use foam above the plywood base. As you mentioned, it can be used to increase height and you can carve into it to form rivers, gullies, etc. Foam does provide some sound reduction, but not as much as you would think, especially if your table is secure. I have some foam on part of my layout because I need a river. Most of the rest of the layout is directly on the plywood.
Horses for courses. Foam is the new kid on the block ( it was promoted by Model Railroader magazine 20 years ago). Both are used for their sound deadening qualities, which we immediately negate by banging track nails through them into the subgrade plywood.
My first layout, which never got finished was 3/4 ” plywood sheets. Cork roadbed, and what fun. Nailed down cork and then had to nail down track.
This time, I studied first — 1/4 ” pegboard with 1″ foam on top glued down. So much easier to work on this time,
Pegboard? Did you get it cheap Jim, or was it a conscious choice? Just askin’.
Sound deadening. I’m not really convinced. Besides until 2010 who’s ever heard a quiet railroad? Half of our club had roadbed nailed to plywood with track attached to roadbed with nails. The remainder had Homasote glue to plywood, roadbed glued to Homasote then track glued to roadbed. Slightly quieter but much more maintenance intensive
Scenery. It’s easier to carve down into the foam than it is to cut away bits of plywood. That being said, there is nothing wrong with laying track directly onto the plywood if you aren’t planning on having scenery bits below the track bed or if you don’t mind cutting into the plywood to do it, that’s how it was done for years.