Aquascaping with Insulation Foam

Using insulation foam as a method to aquascape a tank was an idea that had been stirring in my head for some months now. Ever since I saw this thread from Reef Central on Tanu's tank, I just couldn't help but delve into this subject further, as I was planning to set up a small seven gallon DIY nano tank and wanted to incorporate this idea into it's design.

Now, with a fair amount of research under my belt, I decided to try my hand at this stuff. For those of you who are unfamiliar with this idea, the basic premise is to spray/apply insulation foam to the back and/or sides of the tank, and then push pieces of live rock, crushed coral, or whatever would look interesting and natural as a backdrop, into the drying foam. The foam dries, and hardens somewhat, and creates a "living" backdrop. Additionally, it allows the un-natural looking plumbing, overflows, etc., to be hidden.

I decided to foam the back, and one side of the cube. Also, I embedded a return pipe in the foam to hide its ugly appearance. First, the foam I used was a rigid polyurethane foam. This stuff can be found at Home Depot, but I bought mine at Menard's for a little over $3 a can. The exact foam I used is called "Great Stuff" made by DOW. The type was just the regular, low expansion, rigid type. There are other types for windows, etc. that expand more, but this is not what I wanted. Here is a picture so you know what to look for:

Next, I decided to test this stuff out on a sample piece of acrylic to practice and to just get a feel for working with it. Right away, I noticed a few things about this material:

  • This stuff is very sticky; about the consistency of a roasted marshmallow. If you have ever felt that gooey stuff on your fingers, you know what I'm talking about.

  • The foam will not adhere to a vertical wall, so you have to lay the tank/surface flat and work on applying the foam to one side at a time. Be sure to allow maybe an inch or a half-inch for some expansion of the foam.

  • This is a one-shot deal. Once you start using it, you have to finish within a few hours, as it seals itself shut. (I, of course, read this AFTER I had casually begun my work on the test piece, and then ran frantically to get everything ready for the real thing!)

I sprayed the foam, let it sit for about five minutes so that it started to expand a little, then added some small pieces of live rock. Then, I sprinkled some crushed coral on top of that, followed by some Southdown sand to give the surface of the foam some more texture.

Next, I began work on the actual tank. I followed the same procedure as mentioned above, only I used more rock and crushed coral. In hindsight, I would not have used the sand at all, or not as much; most of it didn't really stick to the foam once it had dried.

I masked off the overflow notches in the back of my tank so that I would still have a working overflow when I was done. I don't think it was all that critical though, as the foam is still somewhat workable once completely hardened. You can quite easily cut it with a knife. Here (right) is a picture of the return pipe enclosed in foam/rock:

Once the back was sufficiently hardened, which took about an hour, I turned the tank on its side and repeated the procedure. Once everything was all hardened and dry, I rinsed it out in the sink, and it was a finished product. (I am planning to do one more rinse tomorrow to wash out any residue that might have been left by the foam).

Top: finished product.
Middle/Bottom: view of aquascaping underwater (with incandescent lighting).

Frequently Asked Questions:

Is this stuff really safe?

Remember that cool kid back in high school? You know, the one that would always try to get you to light up a cigarette, or take a drink? "C'mon man, everbody's doin' it; it's not gonna hurt you…" Well, I am certainly no chemist, so I will resort to the age-old tactic of peer pressure.

This practice of foaming is somewhat popular in Europe, and it's also used in the construction of public aquariums and Koi ponds. While it is usually done on planted freshwater tanks, there have also been several aquarists that have used the foam in reef tanks and reported no ill effects.

I would, however, recommend at least rinsing off the foam and waiting a few days for it to fully cure before putting it to use. I have noticed that water slowly seeps inside, so to ensure a proper cleaning, perhaps a soak instead of a rinse would be more beneficial. And if you're paranoid like me, you can always add some carbon to your filtration regime to cover all the bases.

What if I don't like it? Am I stuck with a "foamed" tank?

There are several ways to get around foaming the tank walls directly. If you really want to try this while your tank is set up, or if you want to keep the foam wall detachable, you can simply spray the foam onto a piece of acrylic, and then attach it to the aquarium wall with silicone, epoxy, or whatever adhesive is most appropriate for your situation. Personally, I just spray right onto the tank walls. There really is little "art" involved, (at least when I do it), just as long as you get the rocks in before the foam cures, you'll be okay.

I also noticed with my test piece that I was able to peel off the entire foam mass from the original acrylic. The foam retained its shape, and the acrylic was unscathed afterward. I can't speak for certain on glass, as its adhesion properties may be different, but on my acrylic tanks, I'm not in the least bit worried that the foam will ruin my tank.

How much area will one 12 oz. can of "Great Stuff" cover?

This will mostly depend on how thick you want the foam to be. In a nano tank, where smaller rocks are used, it is not necessary to spray on a very thick layer of foam, so you could expect to get up to 2 sq/ft per can. On the other hand, if you are going to use larger pieces of rock, a much thicker bed of foam for the rocks to sit in will be needed. For thicker backgrounds, expect to get 1 - 1.5 sq/ft per can.

Remember, you are trying to embed the bulk of the rock in the foam; take this into account when deciding how much foam to use. If the rocks are simply set on top of the foam and they aren't pushed in, or they don't sink in from their own weight, the foam may partially pull away from the rock as it cures, creating the potential for the rock to become loose or possibly fall out of the foam completely. This is why I don't recommend using sand or smaller pieces of crushed coral - they can't adequately be pressed into the foam.

If you have any questions about this article, please visit my author forum on Reef Central.

Reefkeeping Magazine™ Reef Central, LLC-Copyright © 2008

Aquascaping with Insulation Foam by Eric Meier -