Foam Is Not Your Friend

We see a lot of people using foam to carve out layout. It has been a popular material for decades now, but it comes with a few serious caveats that must be addressed. I learned them again recently when building the 4' x 8' layout and was forced to start again. The issue was simple, the 2" inch pink foam didn't provide a level surface to run trains. At first, I tried to shim my tracks or use spackle to make it level, but it wouldn't be a very good long term solution. I felt I had poorly glued the foam sheets to the plywood, hence making it warp.

The spirit level never lie... This is a significant dip here.

However, after removing the foam, I did some detective work and started to measure each panels. The thickness varied greatly from panels to panels, with discrepancies worst at the edges. Just to be clear, the panels weren't flat slabs, but having a bulge in the middle like loaf of bread or a cake. The variation was also more important than I thought. After ripping the panels in 2" wide slices on the table saw, I found the following dimensions.

On the edges, for maybe 8", each the panel was 1 15/16 inch thick, then it raised to 2 1/16 in the middle. That was a 1/8" variation across less than 12" (given the "summit" was right in the middle of the panel). No wonder my track was wonky and large wheelbase steam locomotives derailed on the turnouts located near the edges.

The front spline is 1/8" lower than the back one...

Since I had elected to rebuild the layout using foam splicer similar to Woodland Scenic ones, I decided to rip an entire panel, then compare all the strips. I kept the ones closer to 2" and rejected the other ones, they would serve for yard or simply scenic work.

While making the foam splines I tried two methods: kerfing them on a single single and kerfing them on both sides (like Woodland Scenics). The strips that are kerfed on both side are much more flexible and work better, so I went with that method. Kerfing on one side results in stiff and less flexible splines. They are OK for large curves, but aren't that great when dealing with 21" and 18" radius curves. So I would stay stick with alternating kerfs on both sides.

Installing foam splines is a breeze and creating easements too... 

Kerfs on each side are spaced by about 1 1/4" so when taking in account the blade thickness, the foam web width is never less than 1/2". The same principle applied for cut depth which is also set to leave about 1/2". It's no science rocket, just take your time and do it. It may take 1 hour at your table saw, but the versatility and time saved at the layout is significant. And you also do waste material at all, which is always a nice thing.