A bamboo ceiling was created for the south room (below) using the two large vigas shown in the bottom photo to support the bamboo poles across the span. The term used historically and today in the natural building community for this cross support is "latilla".
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The bamboo poles were precut to length and holes drilled at the proper spacing between the vigas to help speed the installation once on the roof. The bamboo poles were secured into the vigas by 4"-exterior deck screws and 1"-washers. The washers helped spread the clamping force of the screw on the bamboo; and the pre-drilled holes helped prevent cracking and splitting of the dry bamboo.
When the bamboo poles were laid-down, careful attention was paid to select a pole whose orientation would provide a 'crown' for better load distribution and in addition; each pole was selected to best match the pole laid-down before it so the gaps between poles would be minimized.
Preparation of the bamboo involved cleaning the poles with an abrasive sponge soaked with a mixture of water, bleach and a mild cleaning powder. The mix of cleaners was necessary because the poles were under tarps for several years and showed signs of mold.
Another major issue was evidenced in some bamboo holes by tiny holes that meant 'powderpost-beatles' were present. Over time an infestation of these tiny mite-like bugs, can turn these poles into powder. In order to ensure the beatles would not (further) harm the good bamboo poles, they were all treated with an insecticide, then wrapped in plastic overnight. Note that 'Borax' will kill these beatles but I was unable to locate borax in time, so I went with the insecticide.
Finally the poles were coated with a wood perservative and waterproofing sealer that helped bring out the grain and color characteristics of each pole (see above photo).
The vigas and latillas are just the start of the roof structure. In the coming weeks, this blog will detail the buildup of the roof from this point forward.