Can you run down step by step how to make a foam background?

“I have a 140 gal. aquarium with a golden dust day gecko and two anoles in it. I am trying to make a foam background like you have in the picture on the tropical terrarium article. Can you give me a step by step process of how you make the background and how you put the peat moss on. Thanks for your help.

Making a Background with Spray Insulation Foam

Step 1: Get the materials

To make the background you’ll need:

  • Spray insulation / polyurethane foam. Commonly used is Great Stuff Gaps and Cracks.
  • Black or brown silicone sealant without mold inhibitors or other additives in it (lots of it).
  • A calk gun.
  • Disposable gloves.
  • Dry peat moss or expanded by now dry coconut husk fiber.
  • Cork bark, driftwood, and/or plastic net flower pots (optional).

Step 2: Position the bark/wood/pots (optional)

You can just spray the foam on the back of the terrarium, but often a better look is achieved by positioning pieces of cork or lightweight driftwood on the back of the tank and spraying around them so they are surrounded by the foam.

You can also add pots for larger plants this way. If you do this, leave the bottom of the pot bare for draining and consider adding silicone to help secure it in place against the glass first if you think it will be heavy.

Step 3: Spray the foam on

Remember, this is expanding foam. It will grow in size so you do not need to cover the entire back of the terrarium. In fact, if you do spray the whole back of the tank it is possible to damage the aquarium. The foam will expand with no place to go and can crack the glass.

Go with less foam, not more. A common mistake is to spray too much foam and it ends up taking away space from the terrarium. All you are trying to do is create a little texture, perhaps another surface to grow some plants, so just add a few strings, more around and below the items you have placed on the back of the tank (if you have) and don’t go making sculptures. Keep it simple and leave plenty of glass showing. Sometimes all that is needed is a few strings in the corners and one or two around the objects.

Step 4: Let the foam dry

Wait a few hours for the foam to set and fully expand. Even better, wait a day or two. It may feel dry to the touch after half an hour but if you add the silicone and peat/coco fiber too soon there could be issues.

Step 5: Silicone. Coco fiber. Silicone. Coco fiber.

Now it’s time to get dirty. Put your disposable gloves on, grab the calk gun and load it with silicone, and squeeze some lines of black silicone over the dry foam.

Then, using one gloved hand, spread the silicone around so it covers all of the foam and all you see is black without any white foam showing through. Use your clean hand to take some fully dried coconut husk fiber (or peat moss) and sprinkle it on until you can’t see the silicone.

Blow any extra coco fiber or peat moss off of the foam yet to be covered in silicone and then apply more silicone, coco fiber, and repeat. Work in sections, not more than 10 x 10 inches or so, otherwise the silicone may start to set and the coco fiber won’t stick to it.

Also, make sure the coco fiber or peat moss is completely dry. If it is damp it won’t stick well to the silicone.

And careful where you put your gloved hands. It’s easy to accidentally smear black silicone where you don’t want it during this part. If you do get some on the front or side of the tank, let it dry and remove it with a razor blade afterwards. Don’t try to wipe it off while wet.

Step 6: Let everything dry

Now is the hard part. Wait. Give everything a good 12-24 hours to set and dry and then stand the tank up. Knock off all the extra coco fiber / peat moss that did not stick. Blow on it or brush it off.

There will be plenty of holes and spots you missed. Make sure those are clean and free of coco dust so that you can apply more silicone.

Step 7: Patch up the holes

Fill in any white foam showing through with more silicone. Cover with coco fiber. Repeat.

Let it dry again and look for more holes, repeat the patching process.

Step 8: Let everything air out

You too. Take a breath. Don’t keep your head in a glass box full of wet silicone too long. Take breaths while working and once it is finished stick the tank somewhere and let it sit for a week (if you can stand to wait that long) or consider aiming a few fans at it.

If you can take the tank outside on a hot sunny day, even better. There will undoubtedly be a lingering smell of silicone, even after a week or so, but this will eventually go away and it should be safe to plant once dry even if there is a smell.

That’s it!

There are of course lots of variations and I hope you come up with some of your own as well. There are also many other ways to make a background. You can try sculpting Styrofoam pieces, silicone them to the back, and cover them in tile grout, afterwards painting with acrylic paint. You can try using spray foam over Styrofoam so that the background is removable. You can experiment using clay and other natural materials.

Have fun.


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