DIY textured aquarium backgrounds

Continuing discussion started in NVCichlid's thread over at http://forum.nanfa.o...h...ost&p=39188, so we don't hijack his show-and-tell.

One method for making styrofoam backgrounds is described on http://www.cichlid-f..._background.php . I'm seen many other articles on the same thing, many using "Great Stuff" or other similar brand expanding spray foam.

I'm curious what other materials you could use that wouldn't be as nasty to work with and less chance of leaching something nasty into the water. How about building a mold in wet sand and casting concrete, with some sort of lightweight filler in it to reduce weight? That's what people do to build home-made rock climbing holds, which are very similar (intended to look roughly like natural stone).

Concrete contains lime and so leaches Ca+ and CO3- into the water unless sealed properly. Epoxies are probably better candidates for casting.

As far as I can find out, Great Stuff once cured is totally inert. You can also build backgrounds from layered styrofoam sheets; techniques for this are well-developed by model train, tabletop war game, and other terrain-building hobbyists.

Here is a thread where a guy uses SikaTop Seal 107 instead of cement. He documents it well. It's a good read and seems to be a sound method for 3D background construction
http://ice1forum.sud...c...lay&start=0

Here is a thread I did on a tank I made using styro, greatstuff foam and Acrylic concrete..
http://aquaticpredat...p...=27956&st=0

I've been meaning to put one up one this site that has a more local flavor in design.
Might start that up this week with a new tank I'm about to set up at my work..

Concrete contains lime and so leaches Ca+ and CO3- into the water unless sealed properly. Epoxies are probably better candidates for casting.

Yeah, it'll leach stuff out, but you can seal it adequately. You certainly need to seal expanding foam sealant in the same way, so shouldn't be any harder to seal concrete. I'd assume concrete is actually easier to paint than foam.

I'm envisioning being able to simply build a quick rectangular wooden form on top of sand (same as pouring a patio) then dig a pattern into the sand, embed some real rocks in the bottom, and then fill it with concrete. The only challenge I see is finding a filler material to mix into the concrete that would reduce weight significantly. Maybe packing peanuts that have been run through a leaf shredder to chop them up a bit? If you made the concrete thick enough, they should stay suspended, I'd think. What else could be used as a lightweight filler?

Why am I so set on concrete? It's *cheap*, and tools and methods for working with it are really well developed and documented.

Edited by jase, 05 June 2008 - 09:48 AM.

I don't see why shredded foam wouldn't work, but I'm not an expert caster. If you're going to be sanding or carving the exterior after casting, you don't want any filler there, so you would need to coat the mold with a thick layer of concrete, then use a concrete/filler mix inside the outer shell. If it's a large, simple shape, a block of craft polystyrene could be used instead.

Concrete is the cheapest option, but getting fine detail is a problem (it can be done, but it is difficult and may compromise structural integrity), as are weight issues. I disagree with your assertion that expanding foam needs to be sealed as thoroughly; coating the foam is an aesthetic, not a water quality, issue, and missing a spot will have zero effect on your fish. I also disagree with your implication that tools and techniques for casting epoxies are not well-developed; this is simply not the case, and a great deal of info is available online.

A two-part expanding urethane foam mixture is used by taxidermists to cast mannikins, bases, etc.; it is non-toxic and should be ideal in the aquarium. The only trouble is its cost and its light weight (it would need some sort of weight in the base if not directly attached to aquarium structure).

Another option would be to use great stuff foam for ponds. Ther is an article in last months Aquarium magazine.

Concrete is the cheapest option, but getting fine detail is a problem (it can be done, but it is difficult and may compromise structural integrity), as are weight issues. I disagree with your assertion that expanding foam needs to be sealed as thoroughly; coating the foam is an aesthetic, not a water quality, issue, and missing a spot will have zero effect on your fish. I also disagree with your implication that tools and techniques for casting epoxies are not well-developed; this is simply not the case, and a great deal of info is available online.

I'd tend to guess that sealing requirements are roughly equal. I've done a fair bit with "Great Stuff" and other brands of expanding spray foam. The skin it forms when allowed to cure in contact with air seems solid, but if you needed to shape it all you expose the foam interior. You might not *need* to seal that, but I think you'd want to. You'd certainly want to seal concrete, but if you missed a few small spots I doubt the amount of leaching would be a problem as long as you do regular water changes and such.

I also disagree with your implication that tools and techniques for casting epoxies are not well-developed; this is simply not the case, and a great deal of info is available online.

Oops, didn't mean to imply that. Yeah, casting epoxy is well-documented and not too hard (that's actually what most rock-climbing holds are), but cost is prohibitive if you were trying to do a large aquarium background. Plus, you've got nasty fumes and such to deal with. I may be wrong, but I feel like concrete would be simpler, even if you couldn't get the same level of detail. I'm not so worried about losing fine detail, though.

A two-part expanding urethane foam mixture is used by taxidermists to cast mannikins, bases, etc.; it is non-toxic and should be ideal in the aquarium. The only trouble is its cost and its light weight (it would need some sort of weight in the base if not directly attached to aquarium structure).

Good suggestion, Newt. Same stuff is used by boat builders and others. Advantage over spray foam would be that you can pour it into a mold and have it fill voids better than spray foam, I'd guess. I'd expect you could pretty easily do some rough estimates of displaced water volume/weight and embed enough rocks in the lower portion of the wall to get negative buoyancy. I like the idea of being able to embed real rocks (as you could with concrete), but not wind up with a 300lb hunk of wall. I might try this approach this summer.

Here is a thread I did on a tank I made using styro, greatstuff foam and Acrylic concrete..
http://aquaticpredat...p...=27956&st=0

Could you post a couple of those photos here? Don't want to register with a new forum just to see them...