I've played around with ferro-cement a little bit and built a tool shed of the stuff -
But my problem with making a roof out of it - especially roofs that need to support exceptionally heavy loads as a root cellars roof does - Is the difficulty of troweling in all the concrete all in one go so you don’t get “cold joints” in the finished shell.
I should think that it would be very weak indeed if it were layered up little by little, but I could be wrong – Seems some folk do it that way.
Seems to me it’s just rebar–reinforced concrete done on a small scale, and with the big stuff I know getting it poured all at once it critical for strength.
I dunno about adding successive layers of wire mesh.
Dunno how you’d tie ‘em into the shell.
In my tool shed I used a cattle panel frame backed on the inside with light stucco lath and covered on the outside with several layers of chicken wire.
The inner fine mesh of stucco lath is essential to keep the stuff you trowel on from plopping through and onto the ground. I experimented with burlap stiffened with portland cement and gave it up and used the commercial stucco lath.
Then with a crew of volunteers we made a go of it and got the whole thing coated in one day.
The finished shell was no where near waterproof so my wife and I added two more layers after that with no wire, just a stucco of cement to try and seal the structure. We eventually used a concrete coating with latex to seal it up.
Well, you can see my post on the subject for full details.
I reckon with a big crew or a stucco pumping machine a feller could coat a pretty big wire structure in one go, but I generally work with little help and on a shoe string budget and don’t always have much help or coin to spend on a project.
That’s why I like concrete block for a root cellar; it’s easy for a feller to stack ‘em bit by bit.
Another problem is you are entirely on your own when it comes to ferro-cement building. No engineer can tell you if it will hold up or cave in on you when you back fill the earth over your root cellar.
Thanks to advice Tobus gave above I’m pretty certain my root cellar will last longer then I ever will.
Eh, I like ferro-cement and my play with it further down the road – I designed a nifty ferro-cement yurt using a simple cattle-panel framework, and I’d like to make a barrel vault out of it someday. But for a root cellar I decided to stick with a ( mostly ) conventional slab.
We poured our slab last Saturday.
Anyone know how long do I have to leave the props in and forms around it anyway??