DIY : Styrofoam Sculptures
Polystyrene (trade name DOW Styrofoam) is aquarium-safe because it's completely inert. After manufacturing, fresh polystyrene is sent to warehouses for 3 weeks to outgas, so by the time it's available commercially, it's inert.
This article documents the assembly procedure for the styrofoam tier shown in the tank above.
Figure 1
This structure (Figure 1) went into a built-in 65g planted African cichlid tank with very hard & alkaline water conditions. This fish-plant-water combination was going to be hard on plants, so I went with a system of double pots for each plant. Lower pots are surrounded by dolomite, upper pots (planted) use fluorite. A similar egg-crate grill was used to protect the root systems, and a foam liner kept the red fluorite from mixing with the white dolomite. Some planting goes directly into the structure. A spot in the center is reserved for a large Amazon sword plant, and indents on both sides were made for Java ferns. To raise the gravel up around the pots, the structure is a 4" high wall. To reduce maintenance, I've created an automated gravel vacuum, by integrated some UGF plates into the structure and connecting them to a Fluval canister. An Eheim canister does the main filtration.
Figure 2
Referring to Figure 2, material used:
A: GE clear Silicone for Doors & Windows
B: West System Resin 105
C: West System Hardener 206 (205 ok as well, but less working time)
D: DOW extruded Styrofoam (better than expanded polystyrene used for packing materials)
E: various wire wheels
F: various rasps & files
G: modified hack-saw blade
H: plastic pots (Canadian Tire) siliconed to Plexiglas base
I: 3 UGF screens
J: plastic drywall anchors
K: plastic egg crate
Figure 3
Referring to Figure 3, red trims were to add surface area for siliconing to glass bottom. Holes in Styrofoam mark locations where anchors were imbedded to lock siliconed layers together. Exposed anchor heads are to increase silicone adhesion to underside (silicone flowed around the anchor head), see Figure 4.
Figure 4
The following assembly order can also be used for making Styrofoam backgrounds. The biggest concerns are to seal any paints used, with the epoxy resin, and to ensure there is sufficient silicone bonding to counteract the buoyancy of the Styrofoam. Water weighs about 55 lbs/cu.ft, where Styrofoam weight about 1.5 lbs/cu.ft, leaving over 50 lbs/cu.ft of buoyancy to overcome.
Assembly procedure:
1) Build cardboard template (tank bottom or back wall for a background). Mark all interferences & clearance needs.
2) Obtain materials (ie: extruded polystyrene, sand(s), paints, rocks to match etc). Use the thickest Styrofoam available to avoid stacking layers (4" is max, when available in H/W stores). I siliconed my layers together. Next time I will try putting epoxy on both sides and while tacky clamping together.
3) Rough cut and dry fit into empty aquarium periodically. A design on paper helps tremendously.
4) Cut, file and trim as desired. Check fit with any accessories (siphons, heaters, filter outlets).
5) Pass a heat source (hot air gun or propane torch) over all exposed areas to seal surface. Exercise caution, as Styrofoam is flammable & toxic. Careful heating will only cause it to melt into itself slightly.
6) Paint. I used white acrylic latex primer but this is not overly critical, if it is fully dry, and then covered over by the epoxy resin. Color can match other rocks used. Darker colours look natural faster but darken the tank. Keep fish colours in mind for contrast. Try to stay close to the colour(s) of the sand which will be used.
7) Apply 1st coat epoxy.
8) When dry, apply 2nd coat epoxy and sprinkle sand over the structure.
9) Repeat epoxy/sand until satisfied with results. My 1st coat was 100% white sand, and each following coat had more brown sand mixed in until the 4th coat was 50/50 white/brown sand, imitating sandstone. Without colour layering, 2 or 3 coats should be sufficient.
10) Prepare surfaces for siliconing. For backgrounds, it may be sufficient to only clean the glass, and use a generous bead of silicone at the perimeter and across the middle. However, I think that this would be insufficient to overcome the buoyancy of a structure at the bottom of the tank. The Styrofoam would lift leaving the silicone on the bottom glass.
To prepare the underside of the structure, I used 3 methods. Exposed Styrofoam was roughened with a rasp and given 2-3 coats of epoxy (which provides better adhesion than Styrofoam in my tests). I install plastic anchors so they were 1/4" above a countersink and flush with surface (the silicone would flow around these providing greater adhesion). Maximize surface contact areas to silicone. Referring to Figure 3, I used red plastic trims and filled areas of the UGF screen with epoxy coated Styrofoam (not shown, see dashed lines).
11) Dry fit and determine how the structure will be held, while the silicone cures (ie: clamps).
12) Apply silicone (clear herbicide-free adhesive, not sealant) to structure, press into place, and remove. By looking at the pattern of silicone left on the glass, add more silicone directly to the glass to fill any gaps in perimeter bead, or wherever needed.
13) For aquarium use, I would allow 4-7 days for curing time.
14) Rinse, by adding water, and then changing it after 1 day.
Note: For bottom structures, a concrete base plate can also be used, instead of siliconing to tank bottom. Run plastic anchors into Styrofoam underside, and seat them into a curing cement-sand mix in a temporary mould. This is more suitable for smaller structures which can be intricately carved with caves, but are still removable for catching the fish.
2004 update:
The structure in the pictures has been submerged for about 2 years now. It has darkened from various algae growths over the years, making it look more natural, but darker. I changed to a large diameter gravel of a closer colour to the rocks used. The potted plants didn't do as well as I'd like, either from the water hardness or the pot restricted water flow too much. If I was doing it again, I'd use thicker silicone sheets (less work fastening them together) and I might integrate more pots (the Amazon sword is doing very well).
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