Articles - Foam Modules
02/07/2015
My plan was to build a completely self-contained, stand-alone modular diorama, made entirely out of 3/16"-thick foam board (e.g. Foam-Cor®). I realized I needed two 4'x8' sheets to build the 4'x'3'x28" 3D box. A local art supply store did carry those, but they are some distance away, and they cost around $18 each. At the hardware store I found 1/2" insulation board for half that price. Since this was an experiment, I decided to go the cheaper route. Below is a scan of a sketch I had made.
Foam Modules
This diagram shows the front view dimensions. It is supposed to become a "shadow box" module.
Foam Modules
This is a drawing of the side view of the module. Actually, it is more of a slice through the module from front (left) to back (right). The brown section near the bottom represents the 1/2"-thick ceiling tile that I'll be using as a roadbed. Since this module is to model a coal yard, I plan to make it one continuous surface upon which the ties are laid (no individual roadbed profiles). The gray below that is the ground-level. Under the ground are vertical strips that will securely hold the "ground" up. There is no surface below that, so those are open (for easy access to wiring, mechanical things, etc.).

At the top of the module is a 1-1/2" space for lighting, hidden wiring, etc. The yellow strip is a diffuser panel behind which the LED lights will reside. The diffuser panels are typically 2'x4', so the back 10-1/2 inches at the top will just have a block of foam board, or a coved sky.
Foam Modules
The insulation board has a very thin aluminum layer on both sides. The first thing I did was cut a 3-foot section off of one of the sheets, which is the top of the module (4'x3'). The top is laying upside-down on the table. I am getting ready to glue the back panel to this, but it needs to be flush with the back edge.
Foam Modules
I have clamped two measuring squares to the workbench. The squares' vertical will provide a hold to the back panel, while the top panel is pressed up against the squares.
Foam Modules
I am using "Liquid Nails for Projects" as the glue, since I am not really gluing foam-to-foam. For clamps, I am using masking tape. This allowed me to pull the back panel flush against the underside of the top panel, and also deal with the slight bow that is in the foam sheet.
Foam Modules
Here is the set-up from the other side. If I may be honest here, the vertical panel you see in the photo is actually the bottom panel. When I tried to install the side panels next, I thought it was odd that they didn't match vertically. After some head-scratching, I discovered my mistake. I should have labeled the panels, but I thought "how hard can it be to keep 5 panels separated?". Oops! Anyway, I removed the panel (the glue takes hours to cure anyway), and put the actual back panel in its place.
Foam Modules
The two side panels were also attached using the same method and using masking tape to act as clamps. I set this assembly aside to let the glue cure overnight. Note that the module is upside-down in this photo.
Foam Modules
By the way, the corners were a bit of a challenge, but a careful application of the masking tape helped bring them back in line.
Foam Modules
Here is the assembly so far, right-side up this time. The glue cured in a few hours. I included the rest of the garage in the photo, to give you an idea of how big a 4'x3'x28" blob is. It was actually kind of a challenge to store it in the garage while trying to park the truck in there as well.
Foam Modules
After cutting the base of the scenery from the foam, I made a number of 5-inch wide strips. These were then glued to the bottom of the scenery base. The front piece (shown in the back in the photo below) is five and a half inches tall, because it covers the front edge of the scenery base. To get that piece to stay flush to the front I used another spare strip of foam, and pushed the scenery base against the cabinets. Some wax paper was used to protect the floor from glue being squeezed out. The weights are used to hold the whole thing in place while the glue sets. Lots of creative items are used to weigh down the 5-inch strips.
Foam Modules
This is what the scenery base looks like when it is right side up.
Foam Modules
Turning it around, this photo shows the back side of the scenery base. This module was going to have a creek flowing along the back of the modeled space, so I tried to mimic its shape and cut a piece of the foam off. I used a jewelers saw blade to make the cut. This piece has a 2.5" strip glued to it underneath, so that the cut-off foam piece becomes the creek's bottom.
Foam Modules
The next step is to install the ceiling tiles which represent the roadbed of the track. The track goes 18.75" into the module from the front. However, after looking at prototype photos, I noticed that there seems to be no elevation change between where the track sits and the surrounding buildings. Therefore I used the full ceiling tiles (12" square) and glued 8 of them to the top of the scenery base. Between the 5-inch strips, the 1/2" foam, and the 1/2" ceiling tiles, this brings the bottom of the ties to be at 6 inches from the bottom of the module, which is what I wanted. Again, lots of creative weights were used to make sure the tiles are glued down. They were a bit of a challenge to slip into each other, because the glue grabs them right away.
Foam Modules
The ceiling tiles add quite a bit of weight to the base, especially since I had been getting used to working with the lightweight foam. When I grabbed the assembly, the front vertical strip broke off. So, the next step was to add the internal framing you see in the photo below. This makes the base a lot sturdier. Tapping on the base, I can tell a difference in sound between the bare foam on the section covered by the ceiling tile. The ceiling tile dampens the sound quite a bit. The foam acts more like a speaker. So, the idea of inserting some sort of insulation material in the cavities may be necessary.
Foam Modules
Back on the workbench in the garage, I am installing the creek bottom (the small section I cut off from the scenery base's back.
Foam Modules
And here is the scenery base being installed. I have a weight in the interior on the left, because the base wanted to pop up there. Pieces of leftover foam and clamps were used on the left and right outside panels to hold them against the base.
Foam Modules
I used the glue to fill in the gaps between the ceiling tile panels.
Foam Modules
So, is this a viable alternative to building a module, either for home layout use or for modular layout shows?

Pros:
1. It is lightweight.
2. It is remarkably strong once the glue has cured.
3. It can be built with a straightedge, tape measure, glue, and a utility knife.
4. Without the top and sides it might be workable/usable.

Cons:
1. The full-enclosure I had built was too unwieldy to be practical.
2. Lots of support is needed while the glue sets (no screws, nails, or clamps can be used).
3. It is hard to cut a straight edge with a razor blade, and only slightly better with a utility knife.
4. Wood reinforcements would be needed to make it compatible with modular setups and to integrate legs.

Although this project, for me, was a "fail", I am keeping this article on my web site, just in case someone is interested in pursuing this idea.
Foam Modules
Attempt #2
Not one to easily give up on what I thought was a good idea, I went back to work on a second attempt using 3/16"-thick foamcore board. I went to Texas Art Supply in Houston to buy five sheets of 24" x 36" x 3/16" Uniwood Fome-cor® foam board ($3.69 each). I also picked up a 24" x 48" x 3/32" cork roll (but that is also available in other local stores; Hobby Lobby has a two-inch wide roll, which is perfect for S-scale roadbed). Two of the foamboard sheets and the cork roll are specifically for the module I am building. To build the basic framework shown in the rest of this page you only need three 2'x3' sheets of 3/16" foamboard.

Cutting List
Based on 3/16"-thick foamcore board, this is the cutting list to make a 2' x 3' module:
    one: 24" x 36" (top board)
    two: 24" x 3-13/16" (front and back panel)
    four: 35-5/8" x 3-13/16" (side and interior panels)
    nine: 7-3/4" x 3-13/16" (interior cross brace panels)
    two: 35-5/8" x 1-1/2" (interior edge brace)
    two: 20-5/8" x 1-1/2" (interior edge brace)
    132: 3" x 2" (interior corner braces)
Foam Modules
I did some research on the Web and found out that many people reported no problems using their table saw to cut foamboard. So, that's what I did. It worked well. The next photo shows the materials I cut (on the left) to glue to the full 2' x 3' sheet (on the right). Some paper "fuzz" was left from the cutting, but a light touch with sandpaper removed those quickly. Not shown are the small 2"x3" glue blocks, which I cut later. A flat work surface is a must for this project.
Foam Modules
I spent quite a bit of time trying to decide how I was going to deal with the fact that the side panels will be edge-glued to the top board, and that the boards all have a slightly curvature to them. I finally had the idea of gluing strips of foamboard to the underside of the top board to form a rabbet. I first marked 3/16" lines along all four edges of the top board.
Foam Modules
I could then glue one of the 35-5/8" x 1-1/2" interior edge braces in place, lining it up with the pencil mark and making sure it stayed straight by using the straight edge (which also kept the top board flat against the work table).
Foam Modules
I then glued the other long one to the top panel, and the two 20-5/8" x 1-1/2" interior braces, which fit in between them perfectly. I now have a complete "rabbeted" edge all along the top panel against which I can glue the side panels.
Foam Modules
I started with the front (or back) panel first, since it spans the entire 24 inches of the module's width.
Foam Modules
I clamped a square to the vertical board. I then placed the straightedge on top of the squares' other leg (not shown) so that it forced them to be at a 90-degree angle with the top board.
Foam Modules
To make sure the entire vertical panel stayed flat while the glue dried, I used a long straight board and clamped it against the front edge of the top panel. In the back, the panel is up against the wall, which provides the counter force. Note that the glue will likely ooze out a bit, so the wood board needed to be pried from the module a little bit (the message here is to not let that board remain attached to the module too long). I used Aleene's Tacky Glue for this entire module's construction. For most of the gluing we are gluing foam to paper, and Aleene's glue works well and grabs fairly quickly, which allowed me to keep working on the project (only taking about 15-20 minutes to let the glue set a bit at each glue-up).
Foam Modules
I glued the other 24-inch wide board to the other side. Next up is the long edge. It fit perfectly between the two shorter side panels. The setup is somewhat similar.
Foam Modules
I used these magnet clamps to hold the corners square while the glue set.
Foam Modules
I used some scrap foamboard pieces in the back to push the top panel against the back wall, using the wood board and clamps in the front. This worked well, and all four side panels wound up flush and straight. This was my biggest concern with this concept of using foamboard to make a module. If the side panels aren't flush and straight, you might as well start over again.
Foam Modules
With all four side panels done, it is now time to work on the interior bracing. I am doing that to make sure the module can handle the occasional move and perhaps somewhat rough handling. Because I put the rabbet edge on the underside of the top board, the interior braces that span across that need to have a notch cut out of them. I made them slightly larger than 1-1/2" long and 3/16" tall.
Foam Modules
I could then glue them into the module. Once three were so prepared, I was then able to glue the long interior brace in place. I used a piece of yellow masking tape to act as a clamp while the glue set (only on the interior braces; I didn't want to damage the paper on the outside side panels).
Foam Modules
So, the interior braces running from left to right in the photo below (the long ones) are one piece. The nine that run from top to bottom are the individual pieces that are placed in between them. They all fit perfectly.
Foam Modules
I thought that the interior braces' butt joints would leave the whole structure somewhat weak, so as a safety precaution, I cut a bunch of these 2"x3" pieces. These were made from the leftover foamboard material. I glued four to each full interior intersection, and two at each end intersection (with the side panels). So, each interior edge joint has two supporting pieces. This module isn't going to come apart any time soon! The only ones I didn't do are the interiors of the outside corners. That is because those are going to receive wooden blocks, which will later allow the attaching of legs, or attaching the module to some other benchwork.
Foam Modules
I bought these 1-1/4" cube blocks of solid oak wood at Hobby Lobby. I didn't feel like cutting my own and risking my fingers on the table saw. I drilled a hole in the center of the block, big enough to allow a 1/4" dowel or a 1/4" bolt to go through. That can be used to mount or install the module on some other benchwork in the future. One block was then glued in each inside corner of the module using yellow carpenters glue (gluing wood to paper).
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And this is the completed foamboard module as viewed from the underside.
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And here it is viewed from the normal viewing angle. I am happy with how it came out. So far the foamboard module experiment is a success, so I am going to keep going with it.
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Conclusion
I started working on the module by applying two extra layers of foam board to represent the sub-roadbed, and then a layer of 3/32" cork to represent the roadbed. Next, I painted the entire top and then went to work on installing the ties. I stained the ties. Later I noticed a slight curvature to the top. I ignored it. I then spent three nights meticulously hand-laying one of the two-foot sections of rail. I got out the level, and noticed that the top had curved even more. I took the module to the garage where I have a large, flat workbench. Much to my horror I discovered that the entire module was turning into a concave bowl! It wasn't just the top, but the entire module. Even the sides. It was like there was a large bowling ball hanging down from the underside-center of the module, just weighing the whole thing down. So, again, I have to declare this project a "fail". Foam-cor board is not good for structural purposes. After a week of working on the module, its sides were already showing some wear from me accidentally bumping into it. The wooden blocks, into which the legs were screwed worked well, but they made the module wobbly. However, I learned a new technique for hand-laying rail, so the whole effort wasn't a waste!

Update
Five months after I posted this web site article, I come across the "Meet Gatorboard" article by Dave Meyers in the May 2005 Model Railroader issue in my library. This article plainly states that Foam-cor board warps. However, Gatorfoam/Gatorplast has a wood-fiber veneer on it that prevents it from warping (the author soaked a piece in water for 48 hours and it fully retained its original shape). Because of that, though, Gatorboard is more expensive. Considering all the time and effort I put into these experiments, hindsight being 20/20, it would have been well worth doing it right. So, if you are considering doing a project like this, use Gatorboard. It comes in thicknesses from 3/16" to 1", and in sizes up to 4'x8' sheets.
Foam Modules