How To Build A Cake (guest post by Jake)

This Gencon we decided we'd dress up as Dad Egbert and Mom Lalonde. They're bit closer to our actual ages than the trolls we were dressing up as on another day. Since I didn't want to do another day in greasepaint, and those zentai suits look hot (and creepy), I would need something other than just a hat and tie to sell this outfit. I needed a cake. But how do you create a birthday cake that can withstand the rigors of the one of the world's biggest gaming conventions?

Foam! Craft foam is light, easily cut and glued to provide a reasonably realistic shell. Great stuff makes a lightweight and easily carved core.

The first step is to make the core. I went about it by lining two actual straight-sided cake pans with Saran Wrap and filling them with Great Stuff. You may have some left over. Since you have to use the whole can at once, I'd recommend spraying the remainder into a cardboard box to use for other projects. Great Stuff is, well, great stuff. You can make a lightweight sturdy core for any number of props (like troll horns). Failing that, you could insulate something.

Foam cake interior with the battery pack tucked inside

I had moderate success with my approach. The foam expanded vertically beyond the confines of the pan in both cases. However in one case the foam defeated the Saran wrap protection and popped out of the pan as well. But I got one core with relatively straight sides that cleanly emerged from its mold. I used an Exacto knife to straighten out sides, flatten out the top, and carve a hole for the batteries.

Yes, batteries. This is an electrical cake. While I cannot confirm that having actual fire as part of your costume props would get you ejected from the convention, it seemed prudent to to use LEDs. You can make some aftermarket changes to them to make them flicker, but that's someone else's department. (i.e., mine - Tracy)

To get the look of candles I cut ordinary drinking straws into 2" segments, and then slit the bottom into quarters to provide a base to attach to the top of the cake. The top of the cake itself was two layers of cardboard, a layer of craft foam, and wax-paper stencil for the fabric paint "icing". First, I glued the foam and cardboard together with the stencil taped to hold it steady. After painting the design on top, I cut away the wax-paper stencil, and arranged my candles. I splayed out the base of the candles on the inner side of the cardboard, taped them in place, and glued in a second layer of cardboard to keep them from popping loose.

Thee it was time for lights. I threaded them through the candles so that there was an LED at the tip of each one, duct-taping the loose wire to the inside of the form. This left about half of the lights within the body of the cake, but LEDs are a relatively cool light, and it didn't seem to cause any difficulty with heat build-up. The foam is opaque enough that you couldn't see the hidden LEDs glowing inside it.

After that it was a simple matter of cutting some craft foam for the sides, and hotglueing the whole shebang together.

Materials used:

  • Hot glue gun
  • Exacto knife
  • Cake pans
  • Saran Wrap
  • 1 can expanding foam
  • 2 18" x 12" sheets craft foam
  • Fabric paint
  • White nylon cord (for "frosting")
  • Electronic innards (see Tracy's post for details)
  • Three sheets of cardboard
  • Drinking straws

Written on September 23, 2015