[Cob] cordwood vs. cob drying

[phil]

I have worked with both cob and mortar cordwood and though I prefer the cob, both work just fine. 



All corwood walls will have shrinkage issues, and all wood "checks." As to air infiltration, the big problem is where the cordwood meets framing that you have the biggest problem, easily fixed with some form of chinking. Where the wood shrinks and pulls away from the mortar may look like a big problem, but in fact should be a small issue if you have insulated the interior cavity properly. The insulation slows down any air transfer.



If you use cob as your mortar, you only have to rewet the cob around the wood and use your finger to reseal the joints. If the wall is going to be exposed to a lot of rain, consider adding lime putty to your cob mix. Less than 5% should work, but where gloves while working.



While it is possible to plaster cordwood, you will have to expect cracks in the shape of the wood underneath due to the mix of materials and their affect on drying. In the northeast, many cordwood homes have been covered in clapboard, according to Rob Roy. 



Lastly, to avoid large checks in the wood, split anything larger than six inches in diameter. The wedges make it possible to use less mortar and make a tighter more pleasing pattern.



Phil



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