How do I make a Great Stuff Foam Background?

Few things catch your eye as well as a well planted, grown in vivarium. Mimicking a lush jungle, vivariums are fairly simple to set up and maintain, especially with the advent of Complete Vivarium Kits. One aspect of vivarium creation that is often overlooked is the construction of a background. We’ve already touched on this subject before with our tutorial on How to Construct a Fake Rock Background, but this blog entry will explore a much more simple, straightforward approach – making a background out of wood and spray foam.


There are several supplies you’ll need before you get started. Needed quantities of the various supplies will vary quite a bit based on the size of the background you’re making, so estimate what you’ll need before going shopping.

 Pick up from a hardware store:

  1. Great Stuff Gaps and Cracks spray foam (red can with a yellow top)

  2. GE Silicone II Window and Door Silicone in either black or brown

  3. Caulk Gun

  4. Latex or Nitrile disposable gloves

 Pick up from a pet store /

  1. Wood (many different kinds are suitable, and what you use will depend on your personal taste.

  2. DRY fine ground coconut fiber (peat moss, ABG mix, or tree fern can be substituted)

  3. Net cups (not necessary, but make plant placement much easier later on)

Things you probably already have laying around the house:

  1. Sharp serrated steak knife

  2. Drinking straws (only needed if you’re using the net pots)

  3. Shop Vac


 Step 1: Cleaning and positioning the Tank

Before you start constructing your background, thoroughly clean the inside of your tank with rubbing alcohol, then let it air dry. This will allow maximum adhesion from the spray foam when you use it. For this build, we’re using an Exo Terra Glass Terrarium. Lay the tank flat on it’s back.

Step 2: Placing the Net Cups

If not using net cups, disregard this step. Net pots make planting the finished background much easier, and allow the plants to establish much more quickly (even epiphytic plants, such as bromeliads or orchids, appreciate a well-draining substrate). Stick the drinking straw in the bottom of the net cup, so any water that accumulates can run out the cup through the straw, and does not saturate the net cup.

Step 3: Laying out the Hardscape

Spend some time looking at the empty tank, and positioning the wood how you’d like it. If usingcork flats, lay them flat on the back of the tank, maybe slightly overlapping some pieces to provide visual interest and some depth. ManzanitaForest Branch, and other vivarium woodscan be placed at angles to resemble ledges, stumps, or root formations. Keep in mind that the bottom 4-5 inches of the tank will be covered in substrate, so there’s no need to extend the background all the way to the bottom.

Step 4: Foaming the Background

Now that the hardscape is laid out, and the net cups are in place, it’s time to use a can of Great Stuff Spray Foam and actually get started forming the background. It’s not a bad idea to wear gloves – if the spray foam gets on your skin, it can make a real mess! Use newspaper or something similar to protect surfaces around the tank.

After thoroughly shaking the can of spray foam, start to apply it in think layers. Make sure to put it on a little thicker around the base of any wood, to insure proper adhesion. Also, cover thenet cups with a thin layer. Do not apply any layers thicker than an inch or so – these will take a long time to cure.

After you apply the foam, let the tank sit for several days, until the foam is cured. If the foam was put down too thick, it may shrink and pull away from the sides of the tank a bit – if this happens, use more spray foam to fill the gaps.

Step 5: Carving the Foam

After the foam has had several days to cure, it’s time to carve it. Using the sharp serrated steak knife, carve the foam so that no smooth surface remains – silicone adheres much better to rough surfaces. Make sure that you carve the foam in a way to expose the ends of the straws that protrude from the bottom of the net cups, if you are using them. This will allow any excess water to drain out.

After you are done carving the background, remove any large pieces of excess foam by hand, and use a shop vac or dust buster to get any smaller pieces out of the tank. These will get in the way during the following steps if they are not removed.

Step 6: Preparing the Coconut Fiber

Coconut fiber comes in two basic forms – dry in a bag, or compacted in a brick form. If the coconut fiber is in the compacted brick form, water needs to be added to expand the brick. However, the coconut fiber needs to be completely dry before use. It can be allowed to air dry, or baked on a cookie sheet in the oven at about 175F.

Step 7: Applying the Silicone and Coconut Fiber to the Background

Make sure to wear gloves during this step. Place the tube of silicone in the caulk gun, and apply a bit to the foam. Using your hand, smear it over the foam, covering it in a thin layer. After you’ve covered about a 6” x 6” area of foam, press dried coconut fiber into the silicone. Don’t put down too much silicone – it will dry before you have a chance to press the coconut fiber into it. Allow the background to dry for 24 hours, then use a shop vac to remove any excess coconut fiber that did not adhere. If any foam is still visible, go back with some silicone and cover those areas, followed by a layer of coconut fiber. Typically, the background cures in a few days, and can be planted. Make sure that there is no odor or vinegar smell from uncured silicone before planting the vivarium.


Constructing a background is an often overlooked step in constructing a naturalistic vivarium. Not only does it add to the aesthetic appeal of your enclosure, but it also provides much more usable surface area for both plants and animals, as well as visual barriers. 

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