So we were building a bathroom. We used bricks, cement/mortar for the foundation but didn't dig the trench deep or anything, mostly just did it right on top of the sand. So for the walls we were mixing straw with mortar and that works great. We ran out of mortar so we switched to clay/sand/straw in various ratios. Mostly clay and straw. We were sandwiching this mix nicely between chicken wire. About 2 inches thick with the intention to coat it in a nice layer of clay at the end. Weekend goes by and we go back out to work on it to find mold and sprouts on our wall. We don't know mold was a cob issue and opted to halt all production for a moment till we figure it out. Should we remove all the portions of the wall that contain clay and just stick with the mortar and straw mix? Also it should be noted that the 8 by 8 structure has 4 4by4s as the corner posts and a few horizontal 2x4s as cross beams. Some of the clay/straw is just resting on horizontal 2x4s as the base. This is our first earth build. Is the mold a temp problem or a long term re occurring nightmare?
Would it be bad to connect the clay to the foundation or just have it suspended on the 2x4s and build with mortar up to it?
The earth it's on is sand.
The weather can be as high as 100 in the summer and down to the 20's in the winter, most other days are 70s and 80s.
I am not an expert, but that looks to be an awfull lot of straw, I was under the impression the straw is there really to stop the daub cracking? (if modern daub is different from historical just ignore my comment)
I think your efforts are commendable! Firstly, mold isn't necessarily a cob issue, it's a straw issue. Most certainly well established within the bales-or at the very least-inoculated, prior to use. Mold can grow amazingly fast especially during the drying process if temperature is in its favor, and it's common to see a bounty of sprouts emerging from damp, moldy bales, even overnight.
The straw looks a hefty amount and I'd agree on the suggestion of a little Borax. Not sure how that would play out on the already-built wall though. Perhaps a garden pressure pump sprayer, but certainly allow breezy airflow into the area. Ideally about 84-86F for 8 hrs will halt mold growth. But it's now Nov. If you've still got walls to get up, relocate and burn any open bales or nearby wet straw and start anew. I would suggest based on your photos to reduce the amount of straw and keep your material ratios consistent.
Also, it appears you've got cob on the ground? I'm not sure what you could do about it at this point; what's done is done. I would however set out your eves aggressively at 3-4ft. Lastly, again if you still have walls to go up, consider using branches proper for wattle, unless poultry wire is all you have. It couldn't be more contrary to earth building, its failure rate being high in most applications.
Best of luck moving foreward!
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