polystyrene & ferrocement pond- build

I'm about to try something a bit different- a small pond made from polystyrene insulation foam sheets with a ferrocement skin.
I'm hoping it will be a fairly easy build, and result in strong, lightweight and clean looking, little above-ground pond.

I haven't made anything out of polystyrene or ferrocement before, so if anyone has any tips and advice from experience that would be cool.
Otherwise I'll just rip into it and hope for the best.

This is my mark II hot wire cutter

Its made from an old drafting machine and scrap timber. It can slide on the x and y axis's and has a 600mm overhang. I still have to attach the wire and power supply, plus build a big base that it will clamp onto.
The foam sheets that I need to cut up are 2400x1200x40mm, so I need a big rig to slice it up easily and cleanly.

did a bit of work today..

I cut up the foam with the mark II foam cutter. It did a much better job than my first diy hot wire cutter.

I loosely put the pieces together to check it fits

^looks like a giant fish box.
The pieces fit together in a lap pattern.
the very rough cuts are from my first hand-held foam cutter. They shouldn't compromise the build because they don't have to be glued to anything.

I'm going to glue it together with styrobond contact adhesive, but first I need to melt out channels to install the bottom drain and pipe work.

The pond will be used to water a vege garden, and will have a fairly complex drainage system.
The pipes will be buried between the layers of foam, so the pond stays simple and clean looking.

No it was very easy to build, just some wood glued together and stuck on an old drafting machine. for the hot wire I ripped apart an old toaster and used the heating wire from that. A line level taped to the top let me know it was cutting at right angles.
To power it I used 3 6v lantern batteries wired in series. I used an old light switch to turn it on and off.
total cost $15

Ta, Its 1200x480x800mm. the walls are 80mm thick so it would hold just under 300ltrs full to the brim.

Well I got the title wrong. Its not ferrocement, its just plain wire reinforced stucco...

But it still works, its just not as strong and quite a lot heavier than real ferrocement. but still very strong.

It turns out that lap joints and contact adhesive are not a good combination:wall:
But other than that it was a fairly easy build. Especially since I probably had a few too many beers whilst making it.

I used 18mm polyethylene pipe for the drainage. I planned on using 30mm pvc pipe, but the fittings would of cost as much as the whole pond. I really hope I don't live to regret that decision.... It was a silly risk and I wouldn't do it again.
I used a piece of wood with a wire loop attached to the battery pack to cut channels to lay the pipe. I thought I had taken pictures, but the combination of polystyrene fumes and beer had me a little confused that day I think.

I pinned strips of real estate signs to the foam, and bent the wire mesh around the pond-

I used a metal ruler and a plank of wood to bend the mesh.
I heated tie wire with a lighter and stuck it through the foam to tie the two sides together.

this is the finished pond-

It took two coats and two and a half bags of 30kg mortar mix to render. Which is about twice what I thought it would take. It's rapped in plastic for a month now, to fully cure the cement.
I reckon it weighs about 80-85kg which is not lightweight, but light enough for two people to move with a little effort.

I plan on making a couple of wooden caps to cover the green plastic taps.

Its very monolithic looking, but it should suit the little courtyard its going to.