New Research on Straw Bale Walls

I was recently told about some new research results that have posted on line. The Canada Mortgage and Housing Corporation (CMHC) has just published a report authored by Colin MacDougall called “Effect of Mesh and Bale Orientation on the Strength of Straw Bale Walls“. The report is co-authored by Chris Magwood and Steve Vardy.

The findings of the study, in general, support what many of us straw bale builders have believed for some time, although I was surprised by one of the findings: plastic mesh by Tenax may actually reduce the compressive strength of the bale walls. Although not discussed as part of the study, I think it is important to recognize that even though the inclusion of plastic mesh may decrease the compressive strength of the bale wall assembly, it can play a role in the lateral strength of the wall.

Tenax does not supply a lot of shear strength to wall assemblies; however, the use of welded wire mesh can supply significant shear strength as disclosed in Cale Ash, Mark Aschheim and David Mar’s study “In-Plane Cyclic Tests of Plastered Straw Bale Wall Assemblies.” If the mesh is used as part of the overal engineering of the structure, then it must be considered from more than one angle. Of course, the purpose of this study by MacDougall was to test one aspect of the wall strength and so isolation from other engineering affects was necessary to achieve clear results.

According to Don Fugler of CMHC Policy and Research: “The report looks at the effects of bale orientation, mesh vs no mesh, and clay vs cement based plasters on the strength of the walls under compression, and adds to the accumulating scientific literature on straw bale wall testing.”

2 Responses to New Research on Straw Bale Walls

  1. Kingsley Fri, June 19, 2009 at 1:00 am #

    The report says that the testers thought the Tenax(TM) mesh reduced the compressive strength of the wall because it somehow inhibited the bonding of the plaster with the straw bale.

    I notice that they did not test the difference between spray-on plaster and troweled-on, only testing the latter.

    Do you know of any procedures that seek to increase this bond, despite the mesh?

  2. Andrew
    Andrew Wed, July 15, 2009 at 7:06 am #

    I don’t know of anything specific; however, I am not sure why this would be their finding. I have used Tenax on several jobs and have never had a problem with separation. It could be that the mesh was not firmly attached to the bales/frame or that the plastering crew did a poor job. Those two things are often the cause of plaster failures that I have seen. The plaster mesh needs to be attached really well to the walls or it will move too much and cause the plaster to crack. In addition, the plaster must be pressed into the bales with a lot of force from the initial placement to the pressing back to make sure that the bond is solid. I have seen people apply plaster with less than strong muscle application.

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