[Cob] rebar

[Anthony Novelli]

Damon,

You offer excellent points, though I would caution against over-generalizations e.g., "we don't need rebar too"; as use of cob purely as a mass wall system *may* be achieved without such reinforcement. But when cob is promoted as something you can build damned near anything with - without the necessary caveats - you end up with those unnecessary collapses and messed up contractual arrangements or botched public projects. History is a great teacher, and it is important to note - as you say - that when used in ways obvious to a careful look at what has stood the test of time, you have a good chance at success. Our egos and other factors can get us into trouble as much in building as anywhere... and that can apply as much to what we don't know to what we do - or think we do. Entropy rules.

Tony

P.S. Just one example... a friend who took what he learned in a cob workshop or two and set out to build a large rectilinear cob home... which had two very tall, very thin (I think they were maybe 12-14" at base tapering to 8-10" at top), finely crafted cob walls running parallel with a glass wall at the end, and large timbers spanning for the roof. Without buttressing, shear or other reinforcement and an appropriately light roof structure this building was dangerous to an extreme, and would have been improved by the benefit (and cost) of code.

P.P.S. One more... a permacutlure teacher of mine that had permitted several straw bale structures showed an example of his work in Latin America, where the straw bale walls were left unpinned, had no bond beam, a serious bamboo truss system, and a TILE ROOF. Each of these systems on their own may be fine, but not understanding the shortcomings as well as the strengths of each creates seriously out of balance structural equations when combining them. Cob would have been a superior choice for this kind of roof system, though long unbuttressed or unreinforced cob walls can be problematic as well.



On Jun 25, 2012, at 1:13 PM, dhowell at pickensprogressonline.com wrote:

> Tony: ...the services of tensile strength that rebar offers in earthen and concrete structures is justified to ridiculous extreme.
> 
> Damon: Possibly. But also, cob has been proven to hold up just fine without rebar. So which side is doing it the right way? Whichever side has the most money, I presume. Generally cobbers are poor people and we all should be able to build our homes with what materials we can afford and not be denied housing because of code costs. There are cheaper ways than concrete, steel and sheet metal. Believe me, I think about what will make my building stand up as I'm sure anyone who looks to build their own home would. Tensile strength is an important issue. I bet after a few collapses and possibly deaths, traditional cob builders noticed the more straw in the wall, the more weather resistant. Straw provides our tensile strength, we don't need rebar too. Cob does have its place and California is hard on it. But they are adapting it to their environment. What is required in one place may not be required in another. Let's not pretend like this is a brand new material that the world has just discovered.