permaculture

["Kirby Fry" <peace@totalaccess.net>]

Hi Paul,

 

I haven't checked out John's or the Lama Institute's site but I've built several ferro-cement cisterns myself.

 

Pounding rebar into the ground is tempting but really it can be a critical error.  Rebar or any steel is not supposed to go directly into the ground.  It will rust in most climates and the rust will travel right up into the structure.

 

Our cisterns had one continuous piece of 20' rebar starting from the center of the floor's tank turning 90 degrees upwards at the wall and bending again at the seem between the wall and lid.  Smaller pieces are used to finish the lid, the important part being that at each joint or seem there is a continuous piece of rebar.

 

A 1 to 3,000 gallon tank doesn't even really need rebar though, and even for the bigger tanks rebar is mostly for stabilizing the remesh until the first coat is up.

 

No footing per say is required simply a two to three inch bottom with all rebar up and away from the ground.

 

In cisterns or anything wet for that matter the galvanized chicken mesh is not recommended, though I have seen it used.  It apparently sets up electrolysis with itself and the steel remesh when moist and ultimatelycorrodes.  And yes it is a labor intensive project, no way around it really except to make the cistern as thin as possible.  At Fossil Rim Wildlife Center the materials for two 6,000 gallon ferro-cement tanks cost us under $700 for both - we worked as slaves back then and labor was not a cost.

 

I think my friend Jack Rowe did not use rebar, lath nor chicken wire.  He tied tar paper to the outside of the remesh and plastered right onto the tar paper and remesh.  Then he removed the tar paper and plastered the outside.  I'll have to double check with him.  He only put on two coats of cement and used the cement adhesive on the second coat.  The tank initially leaks but self seals over a couple of months as the lime and fines seep through and eventually fill the cracks.

 

Personally I would have troweled or brushed on a high lime liner on the inside, I believe it's, 1 (lime): 2 (cement): 3 (sand).  This can be eggshell thin or troweled on and provides lime and fines to seep through cracks and fill them.  I would stain or paint the tank after the cracks have sealed - not always an option though.

 

As far as I know the tanks can get pretty big.  20' in diameter by 9' tall (two bands of 5' wide remesh overlapped 6") is common here in Texas, I believe that comes out to around 22,000 gallons.  The 35,000 gallon tanks I've seen are usually formed and poured - talk about a lot of work!

 

My dream is to build a basement that's a cistern, so the walls of the cistern serve as a footing for the house and the poured lid can be polished, stained and etched serving as the fist floor as well.

 

Good luck,

 

 

Kirby Fry

 

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