Hi,

I am new to this forum but I am not sure why because it looks like a great resource. Anyway I am converting an old hottub room which was an addon to our house to an atrium/greenhouse. The goal is to have both an extra living space and a place to grow seedlings and other plants.

As part of this I have been planning to incorporate a long narrow cistern into the wall. As far as I can tell ferrocement would be my choice because the walls don't have to be super thick and they are durable. I plan to use the cistern for heat/cool storage as well as rainwater storage. It will have an open top initially and I will probably build a wooden cover.

My question is, how do I figure out how much iron I need to put in the walls for them to be stable?

Since it won't be round but sort of L shaped it won't have the weight of the water spread out evenly along the walls. My understanding is that the round shape contributes significantly to the stability of this sort of tank.

Also I was wondering if its OK to use scrap metal? Up here we have a lot of oil drilling :( and there is really heavy duty drilling pipe that I can get fairly inexpensively. We have used a bunch to build trellises outdoors but I was thinking of sinking some deep into the ground at intervals in the walls of the cistern to give extra support.

Any shared experience, resources, or advice would be greatly appreciated.

Thanks,

Kate