Ferrocement is an excellent, well tested building system used throughout the world. This post explores two earthbag structures on our Projects pages that have ferrocement roofs.
For small projects, simple curved shapes of ferrocement make a good roof. See EarthDome House. In this project they used rebar and mesh for the roof and recycled polystyrene for roof insulation. The author provides sufficient detail to enable DIY builders to build a roof like they did.
For large structures, see the method used on the Large Arizona Shop. They built arching trusses fabricated from 5/8″ rebar. Trusses were covered with expanded metal lath over stock panels, wired on using safety wire. The roof was coated with 1/2″ non-shrink construction grout.
I have found a local (almost) supplier finally for the magnesium cement and an article about a beautiful Gekko Sculpture -but the artist used a combination of portland cement and sand with only 15% magnesium oxide plus flyash and an additive called Clinoptilolite…hmmm.
The fellow who runs the company is a cement scientist and very busy but i will try to find out more about this.
What i really wonder is, if portland repels cellulose, then why does my concrete work so well with sawdust, cloth, and paper in the mix? I now add acrylic (bondcrete) and Lime Putty to my mix but not at the beginning and it still worked???
the link to the beautiful Gekko (and the company, Tec Eco) is:http://www.tececo.com.au/files/newsletters/Newsletter73.php
Thank you very much for contributing. This is an important topic we’re still learning about. More research is necessary. Does anyone else have comments?
i am so happy i found your blog- i have been deeply engrossed in experimental concrete work for a while now, especially interested in roofing issues-i have been working with concrete dipped cloth for walls and am now developing a roof system- will look forward to your posts!
Be sure to read this post about magnesium cement: http://earthbagbuilding.wordpress.com/2010/03/05/magnesium-cement-for-roofs-and-plaster/
When applied to walls, it’s typically called cement plaster or cement stucco. Some people have used cement plaster on earthbag (and straw bale) walls, but I don’t recommend it. It’s best to create walls that allow water vapor to pass through. This is less of an issue if you’re filling bags with scoria or similar materials not affected by moisture.
My preference for plaster by far is to use wide roof overhangs and earthen plaster. It’s dirt cheap, easy to work with and non-toxic.
Funny you should mention this. I was considering building a small dome as my first test structure, but truth be told I’m not crazy about the Conehead-like look of those. So now I’m leaning toward a roundhouse (like your article on the earthbag site), and will probably opt for a ferrocement roof on top of that. First though, I have to finish the ferrocement shed that I started late last fall. Got the idea for it here…
http://www.i4at.org/surv/ferro.htm
…and thought it would be a good test structure to see if I like the medium. Do you think ferrocement would make a good outside plaster for an earthbag structure? Or do they need to “breathe” like straw bales?