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Making Sand-Cast Foam Terrain

By Andrew Pieper aka TaleSpinner

About a year ago, I was spraying Great Stuff into some cracks in my house when a thought struck me, "This is liquid foam! I can make terrain out of this." I got a tub of sand and started trying different things to cast the foam. Many of my initial attempts really didn't work, but I could see the potential. After much trial and error, I came up with a method that produces beautiful terrain, for less than a dollar a piece.

Materials Needed:

  • Tub with a flat, level rim
  • Flat board large enough to cover the tub
  • 1 to 1-1/2 inch (3 cm) drill bit
  • Electric drill
  • Waxed paper
  • Tape
  • Sand, enough to fill the tub to the rim
  • Water
  • Great Stuff Large Gap Foam Sealant
  • Disposable gloves
  • About 20 to 30 lb of weights.
  • Paint and whatever terrain materials you need for finishing the piece


1. Drill a 1 to 1-1/2 inch (3 cm) hole through the center of the board.
2. Cover the board in waxed paper and tape it to secure it.
3. Cut an X in the waxed paper through the hole in the center of the board and set the board aside.
4. Fill the tub with sand.
5. Add water and mix it with the sand until the sand is moist and sticks together in a ball when you squeeze it.

6. Ensure that the sand is slightly higher than the rim of the tub, all the way around the rim.
7. Scoop sand out of the center of the tub to make the terrain mold. Remember that this is a negative of how you want the actual terrain to look. The deeper you dig, the higher the terrain will be. Be creative and sculpt whatever features you want in your terrain into the sand.

Note: You don't want a lot of loose sand lying around; pack all the sand together into the mold.
8. Place the board over the sand and press it down to the rim. This will even out the edges and seal the mold.

9. Remove the board and touch-up any loose sand that fell into the mold in the last step.
10. Put on your protective gloves and spray the foam into the mold, ensuring that you spray it liberally at the edges.
11. Place the board over the mold with the hole over the deepest part.
12. Stick the foam straw into the hole in the board and spray the foam until it comes out of the hole.

Note: It is better to spray too much in the hole than not enough. Sometimes, after spraying, I place my gloved hand over the hole and press down for 5 minutes to allow the foam to fully expand inside the mold. The foam will continue to expand and come out of the hole for the next hour or so. If it does not, you probably did not spray in enough foam and some of your detail may not get cast into the foam; see the following picture:

13. Place weights on the board to hold it down as the foam expands. The foam will expand out of the hole.
14. Wait 24 hours for it to dry. (Drying time may vary based on the size of the terrain you are making.)
15. Break the large chunk of foam off of the top of the board. Check inside the hole and see if the foam has fully cured (i.e., not gooey).
16. Lift the board and foam terrain out of the mold and flip it over. If the foam had not fully cured, let the terrain stand until it does.
17. Brush the excess sand off of the terrain.

Note: A lot of sand will be permanently embedded in the terrain. This gives it a dirty/rocky texture. You can vary the texture of the surface by varying the coarseness of the sand you use.
18. Break the terrain off of the board.
19. Cut the sprue off of the bottom of the terrain.
20. Allow the sand and external surfaces of the terrain to dry before you paint it and finish it.
Note: The terrain will shrink for a week or so after casting it as the foam continues to cure. After that, it will gradually return to its original size and shape.
And the final product:

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