Foam on Plank Module Construction
Why foam on plank
Foam on plank module construction can be a quick and easy method of building quality T-Trak modules while also providing some creative freedom for modeling elevation change and ground contours. Modules can be built in a fraction of the time of standard wood box modules because they are simply just a square of foam and a square of wood glued together. With the foam on the top and the plank on the bottom, you can easily cut, carve and shave to create streams, rivers or other depressions that would be a challenge with a standard rigid top module.
What is foam on plank
Foam on plank module construction is basically rigid foam glued to a solid base. The foam is insulation styrofoam purchased from a home improvement store. Usually blue or pink, it comes in 1 inch and 2 inch thicknesses, and in sizes from 2 feet square to full 4 x 8 foot sheets. As of this writing (January, 2016) a full sheet of 1 inch foam is $20 and 2 inch is $30 in my local area.
The plank can be any rigid material though I prefer to use 1/2 inch exterior plywood. However my modules have a mix of 3/8 and 1/4 inch plywoods of interior and exterior grades, whatever I have lying around. You can also use MDF or even nothing at all, though that technically is foam module construction which is not yet covered here. I have found 3/8 plywood with 2 inches of foam to be very rigid for use in triple length modules without the need for wood side supports.
Legs or feet for the module are the same as the standard module legs. Personally I prefer the slightly more expensive threaded furniture glides. These are a 1 inch round smooth metal foot on a 1/4 inch threaded shaft. I then add an adhesive 1 inch round felt pad to protect table tops. Another advantage of threaded furniture glides is they come with their own plastic version of a t-nut, saving needing to purchase t-nuts separately.
There are some definite benefits and pitfalls to foam on plank module construction. First the good news. Basic module construction is quick (I was able to create two 90 degree corners, two 180 degree corners and two junctions in about 2 hours, before adding track). There’s no complicated joinery. Legs or feet can be added directly into the base board and placement is flexible to suit your scenic or support needs. Costs are low. For a deep single module (about 12-1/8” x 14”) the cost is about $1.40 for the foam, perhaps another $1.40 or so if you need to purchase plywood, and $1.50 for the t-nuts and bolts for the standard feet. And with foam you have easy elevation change.
The pitfalls are that foam is delicate. Without covering (such as a plaster-like coating of scenery or rigid side panels) the unprotected foam easily gets dings or finger indentations if they aren’t handled carefully. Track has to be glued rather than nailed, and I find I need to apply extra glue (a second layer) in order to keep it secure, especially where the track begins at each end of the module. And while you can cut foam with blades, saws and rasps, by far the best tool is an electric cutter which is an added expense. I’ve had good luck with a floral cutter ($20 at craft stores) but they are fragile. More expensive models like the wire cutter from Woodland Scenics would be durable and provide additional flexibility. Styrofoam cannot be glued with CA or spray painted with common paints such as Rust-oleum. Both will melt the foam like acid.
How to make basic foam on plank modules
1. Cut out the plywood base to the exact dimensions you need for your finished module. I like a little extra gap between my modules so my modules are 2mm less at each side than the track. I also like full depth 14” modules. So my single modules are 306mm wide by 14” deep. If you don’t have the tools to cut the plywood, most home improvement stores will cut if for you for a nominal cost.
2. Cut out the foam. You can go one of two ways here. Initially I traced my plywood shape onto the foam and then cut the foam. However as time passed and I made more modules I found cutting the foam a little larger (such as 1/2” all the way around) and recutting after the glueing process produced a nicer, perfectly trimmed fit.
3. Glue the foam to the plywood base. I use Mod Podge but any white or wood glue is sufficient. Apply a good even coating, apply the foam to the plywood, and weigh it down with stacks of books until the glue is dry.
4. If you over cut the foam in step 2 like I do, now is the time to trim the foam. Clamp a straight edge on top of the foam inline with the edge of the plywood base. Trim off the excess foam with the electric cutter. Continue for all four sides.
5. Install the feet. Mark the placement of the feet and drill a hole through the plywood to accept the t-nut. Apply a little glue and tap in the t-nut. Screw in the machine bolt or furniture glide into the t-nut.
6. Glue on the track.
I will add instructional photos and photos of finished modules hopefully in the next few weeks or so.