It is important to understand that bales are made of a material that will compress over a period of time, therefore if you do not pre-compress the walls at the raising stage then you will need to wait for a settling period before you start rendering the walls. This settling period will depend on the density and quality of the bales, and the weight of the roof. If you do not wait for a period of compression before you plaster, then you will have trouble with cracking and you will get problems around the windows and doors. To get the rendering under way quickly there have been several methods of pre-compressing the walls used around the world, but the method we prefer is the grippling method.

We like the grippling method best because it requires few tools and uses manual labour. We use 2.5 gauge or 2.5 mm high-tensile wire to tie the strawbale walls from the bottom plate up to, and over the top-plate assemblies. We use one tie-down every 450 mm or two per bale. The medium gripples are placed on opposite sides so we can get even pre-compression, so you don’t end up with a lop-sided top plate. We can normally, with good strong bales, achieve a pre-compression of 50 mm.

John Glassford shows the profile of a loadbearing wall with tensioning wires running vertically up the wall through holes drilled in the timber bottom plate.