Another Miami Layout

[nachoman]

I wound up using a combination of MDF and 1/2" plywood over an L-girder framework. The MDF is not the best stuff to use, but I am on a budget and it came free courtesy of my dad's new home construction. Since I didn't have enough MDF, I also used plywood that I got for free. One day, there was a man walking down the street near my house carrying a 3'x6' sheet of plywood (for who knows why - I think he found it behind a store at the corner that sells windows and doors). It was hot outside, and he asked if he could put it under my carport until he came back with his truck. I told him fine. A month later, he had never come back, so I used the plywood for my layout. Neither of these materials are ideal to use, but I have built layouts with low-grade plywood before. It works fine as long as it is properly supported.

The knotholes and irregularities are really only an issue if they are under where the track will go (you don't want dips in your trackwork). I would suggest a floor leveling compound from the home center to fill those holes. Just trowel it on and sand it down. No need for any kind of cloth or newspaper.

Since your entire layout has a plywood base, the white foam will work perfectly fine as a track underlayment. The drawbacks of the white foam are that it is not as strong (unimportant if it is laid atop plywood) and that it is messy to cut and shape (I don't see any mountains or terrain on your layout). If I was in your situation and concerned about knotholes in the plywood causing dips in the track, I would go to the home center and pick up a sheet of 1" thick white bead foam, cut it to match the plywood top, and glue it down with liquid nails or gorilla glue.