Foam Topped Modules

In the tutorial on how to make a quad module with no pieces long than 48 inches long, I mentioned the foam tops I use. I've had a couple of requests for further information. Looking at some photos, I realized there really isn't any good way to show people what's involved unless you take pictures as you're building one, and it was too late for that this time around - so I fired up Sketchup and did a few drawings that I hope will make things a little more clear.

Pros and cons of Foam Tops

Advantages of foam tops

  • Extremely light weight
  • Surprisingly strong in module sized pieces
  • Stable over a wide range of temperatures and humidity
  • Water resistant - landscaping materials won't affect it
  • Easily sculpted with simple hand tools
  • Quiet to work with - ideal for those living in apartments
  • Can sometimes be salvaged from construction sites - ASK FIRST!
  • Easily bonded with Gorilla Glue or low-temperature hot melt glue (my favorite)

Disadvantages of foam tops

  • Susceptible to damage, especially on edges
  • Petroleum based paints and adhesives will destroy it
  • May act as a sounding board, slightly increasing noise level depending on size of module
  • Can be messy if you need to do a lot of carving on them - keep a small shop vac handy!
  • "Foam adhesives" for construction work may or may not work well with it - I don't rely on adhesives for attaching to framework, I ALWAYS use some kind of mechanical fasteners as well.
  • Usually comes in nothing smaller than a 4x8 foot sheet. If you have a small car, you may need to cut it just to get it home.
    • NOTE: Lowes now offers a 24 x 24 inch piece of their house brand one inch thick foam for around five dollars! It's big enough for several T-Trak modules and… it's already green!
  • If you want to put a water feature on the foam topped module, it is necessary to seal the foam before painting or pouring the water - I didn't the first time and ended up with a river full of bubbles. The same lightweight spackling I use for smoothing and filling gaps will do the job here, too.

Get the Right Stuff

What you want is a sheet of extruded polystyrene foam. It comes in several colors - I've seen it in pink, blue, and green. Some varieties have a plastic film vapor barrier that needs to be removed - it peels off easily.

You do NOT want the white "beaded" foam that is often used in coolers or ice boxes. While it may be fine as an insulator, it is completely useless as a module material. It is extremely weak structurally, almost crumbling under load, and disintegrates into the componant pellets if you try to shape it.

How to use it

When you've finished the basic framework, turn the framework upside down on the foam, then take a Sharpie or similar marker and run it around the inside, marking the cut lines on the foam. A utility knife or razor blade is neat, but the foam is really too thick to cut that way. The best method generates some "foamdust", but is much easier. Use either a hacksaw blade (outside of the frame - wrap some duct tape around it to make a handle if necessary) or use a Japanese style flush cut pull saw to cut the foam to shape. Keep the sides as square as possible, and cut to the outside of the lines you drew. It's OK if the foam top is a tight fit in the frame.


Single module with foam top inserted

Here's a line drawing of the foam fitted into the quad module.


Quad module with foam top inserted - Click to view full size and resolution

Once the foam has been fitted into the frame, I drill holes into the sides about 1/2 inch from the top of the module that are sized to be press fits for bamboo barbeque skewers, about 4 inches (100 mm) apart around all sides of the module. I cut the skewers into pieces about 3 inches (75 mm) long, squirt a little Gorilla Glue into the hole, and drive the bamboo "nails" into place using a tack hammer. This secures the foam into place and makes it impossible to remove without destroying it completely. These transparency drawings show how it all goes together.


Quad module with foam top inserted - Click to view full size and resolution


Quad module with foam top inserted - Click to view full size and resolution

You might notice the corner blocks are drilled completely through and are mounted flush with the top of the module. This makes the entire module stronger (they are glued and nailed in the corners) and makes it possible to adjust the height of the module from the top… I also cut a slot in the end of my adjustment bolts so I can use a slot-head screwdriver from the top of the module.

When the foam is in place and the glue has dried, I fill the gaps and crevices between the sides and the foam with lightweight spackling, the material Woodland Scenics sells as "foam putty". It's an extremely lightweight material made for patching holes in plaster or plasterboard, cleans up with water, and dries surprisingly hard, but sandable, in a very short time. There are several brands - the most common one in my area is "DAP Fast and Final Lightweight Spackling"

Once the gaps have been patched and dried, I just lightly sand to smooth them, then finish the module. The finished surface of the module before landscaping looks like this:


Single module - gaps filled and smoothed - Click to view full size and resolution


You can build up layers of foam for landscape features by using low-temperature hot glue to build "wedding cake" tiers, then sculpting them with a Sur-form shaver or similar tool. Keep a shop vac handy to clean up the mess, you're going to generate a lot of "foamdust". You don't have to limit your landscaping to the added tiers, either - using the same tool you can cut into your base and give it a gently rolling profile that isn't really practical with other techniques, and the small size of the modules allows you go a little deeper with these landforms than might otherwise be safe without sacrificing the strength of your module.

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