[Cob] Sawdust and shavings in cob

[Lance Collins]

At 06:07 10/06/2009, Mia wrote:
>Does anybody have experience using sawdust or shavings in the actual 
>walls and not just in plasters?

Not cob exactly but I experimented with various mixes to make blocks.

A mix of half soil and half sawmill dust worked very well.  The 
blocks were strong, dried quickly and were half the weight of soil 
alone and thus were easy to lay on the top of the wall I built.

The sawdust was from the breaking down stage of milling.  Looking 
with a magnifying glass I saw the 'dust' was actually shredded pieces 
of wood about a centimetre long not at all like the dust from cabinet making.
Also my soil may be unusual.  It's broken down mudstone and makes a 
good cob with any additives.

There were a few left-over blocks in a small enclosure which were 
exposed to the bushfire we had on Feb 7th.  After baking at 1000 deg 
for a few minutes the blocks had so little strength they were hard to 
pick up without crumbling to a fine powder.
For those of concerned about carbon emissions I've seen estimates 
that we put 100 million tonnes of carbon dioxide into the atmosphere that week.

Lance
(in Aus)