Some people are using sharp rocks, thorny vines, etc. to prevent slippage between bags. These things may help a little, but barbed wire does a lot more than prevent slippage –– it adds tensile strength to your structure. This point is often overlooked. Tensile strength restrains courses of domes from moving horizontally (expanding outwards from the weight above). Tensile strength also helps hold corners of buildings together. For instance, over time a corner could separate as the walls of a structure lean in different directions. But proper use of barbed wire between courses would help prevent this from happening.
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I have heard that you should use two strands of barbed wire per row. We are building a 4m diameter dome out of WPP tube. We are in a non-seismic area. Do you think this is suitable?
It should be okay because it’s small.
It seems to me that barbed wire with mesh bags (hyperadobe) would be a belt and suspenders sort of approach. It’s probably unnecessary in most areas, and adding some expense (albeit not THAT much – barbed wire is pretty cheap, relatively speaking), but it certainly cannot hurt anything.
Good point. Some people may be focusing too much on cost and speed of construction versus strength and durability. We try to present both sides and let people decide what’s best for them. But for sure barbed wire is not terribly expensive and it does add a great deal of strength.
What about replacing barbed wire with knotted nylon rope. Would it be as strong? Maybe it will be more durable since it will not rust? I think it would probably be cheaper than wire.
Thanks Owen for your earlier comment on this topic.
It all depends on the details. Small, simple structures in non-seismic areas are not nearly as critical as those with long straight walls. Everyone will have to decide what makes sense for them on a case by case basis. But I don’t see rope adding much tensile strength because the bags might still slip. It doesn’t seem like a few knots will hold nearly as well as thousands of barbs.
Necessary even for mesh bags? I thought you were suggesting the little bit of clay sand mixture coming through the mesh would allow for tensile strength? So use barb wire even on mesh bags?
Most people use poly bags, so that’s what I was referring to. Mesh bags probably don’t need barbed wire on small buildings in non-seismic areas.