by Andrea Madeley

Introduction

I have a 2' cube destined to become the new home for some seahorses and wanted to maintain as much open area as possible to provide room to plant some macro algae (for hitching).  So I made a coral rock wall and bridge, made from dead coral that should in time become alive.  In time it is hoped it will support some soft corals with the ledges.  If done again, would make the wall section in two parts, making it easier to handle and install.

DIY rock installed in the tank.

Side view of rock in tank.

Front view of rock in tank.

Materials

• Eggcrate
• Bleached / dead coral - various sizes (pieces smashed up with a chisel and sledge hammer gives lots of options)
• Black Waterfall Foam, 2 cans used in this project, appears to be only available from www.waterscapesaustralia.com.au @ $37 a can
• Epoxy resin.  Note that is not a fibreglass (polyester) resin and can be harder to find in a hardware store.
• Putty (aquarium safe) for gap filling
• Fine sand and courser coral sand for top layer
• A Dremel tool or similar is handy.

How To Do It

Step One

It is a good idea not to attempt building a structure out of the foam without a support structure.  Eggcrate is something handy to use as this and also provides something for the foam to grab onto.  There is a decent amount of weight in the wall, and without something like eggcrate, it is likely to break.  Depending on the location of the wall, plan to leave some sections cut out, such as to accommodate a powerhead or allow water to flow to the overflow.  Also ensure that you consider the size that will be able to get into the tank, as the tank braces do take up space.

Starting structure of eggcrate to support the wall.

Step Two

Take the black expanding foam and get to work squirting and setting the rocks. The foam expands around the rocks, so it is best to place the rocks on carefully and resign to the fact that a lot of the foam will end up being cut away.  The foam deflates as the rocks are set into it.  Timing is important, you want the rock on in time to stick to the foam (so before it begins to lose it's tack), but not so soon that it completely gets engulfed by the expanding foam.  The can of foam has to be used in one hit.  Best to plan where each rock is going before hand.  Any foam that gets stuck to the rock can be removed by sanding.  It is best to get the foam under the rock so that the supporting structure can absorb the foam too.

Rock embedded into the foam

Close up of rock embedded in foam

Start of a bridge piece

Step Three

Now let the foam cure.  For any of the curing steps, best to keep the pieces flat, to avoid any deforming.  Once it has, get to work cutting the foam away from the rock using a nice sharp knife. A hobby razor blade is ideal for tight areas. A Dremel tool can be used to sand the foam back, the foam sands really well.

Step Four

At this point you apply the 2 part epoxy resin. Simply pour and spread with a paint brush (and artists brush is best). Then, using a sifter, sprinkle the finer sand over the epoxy. Let this layer of epoxy and sand cure. Now apply another good coat of epoxy , then pack the coarse coral sand (e.g. 3mm) and pushed the sand on firmly.

Any area of the foam that is cut back needs to be well sealed with epoxy, otherwise the foam will soak up the water. It is only the skinned layer of the foam (pre cutting / sanding) that has the water proof membrane. Don't worry if you get sand on the rocks - it blends in and what you don't want you can Dremel / sand away. Finally I made ledges (which a probably hard to see because of the front view) and these are basically pieces of the dried coral stuck to the set in rock with Aqua Knead It ... and then well covered in sand to hide it. I also used bits of silicone here and there because the sand sticks better to that.

Caption

Final Product

The finished wall piece.

The finished bridge piece.

Finished bridge piece, close up of top section

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