Cob is Resilient! Cob Bed Demolition Photos and Video

by ziggy on June 18, 2010 -- 4 comments -- Follow


Unbelievable. This is the third incredibly wet year running now. Rain, rain, rain. It really gets old. (And mucky.) But that didn’t stop us from the cob bed and bench demolition project inside of my house. I had been dreading this task for a while now, but boy am I glad we got it accomplished! And it wasn’t nearly as bad as I thought it would be to destroy thousands of pounds worth of cob… but normally, you cannot really say that of cob, because it is so incredibly tough and resilient!


Last week, April, Snack (Wabi-sabi’s work exchanger), and I went about destroying the cob bed in the house. We moved out into a tent, and shoved everything in the house into one corner, protecting it with a tarp. Taking apart that bed was not going to be a clean task.

With pick axes in hand, we took our first swings at the bed. The pick axes left hardly a mark! Those first 8 inches of material were bone dry and nearly as tough as rock. It took serious effort to dislodge any significant amount of material, with lots of sweat and pauses for achy bodies. This video should give you an idea just how strong of a building material cob is:

Thankfully, the random rubble mixed into the bed made it slightly easier to remove larger pieces at a time. But I don’t wish this task upon anyone. Taking apart cob is really, really difficult.

As we got further into the project, we hit stovepipe (literally). It was impossibly to avoid not destroying the stuff, unfortunately. It was sad to see but it had to be done.


As we got deeper down, the job suddenly became easier. The material was actually wet about halfway down, around and underneath the stovepipe. Hm! It seemed as though the bed never dried after it was built. Without exposure to the sun and wind, cob takes a long time to dry, especially in a humid environment, and especially when it’s in a thick form. I’m still guessing that it never fully dried, but it could also be that the stovepipe condensed in the cold, and the moisture ran down throughout the mass, making it damp over winter. Either way, this cob crumbled when we hit it.

Seeing this problem, I was relieved that we were removing the bed from the house. I knew that this would have caused serious problems down the line. A damp bed against the exterior walls of the house? Not good. Around the edge of the bed, the straw in the cob walls was actually rotten at the ends. It smelled like mold. Mold = really not good. Yeck.


Archaeological dig or cob demolition?

Destroying the whole bed and bench ended up taking about a full day of work. We carried all of the cob out in buckets and filled a whopping dozen 55 gallon drums full of the stuff. That’s a lot of material!

When all was said and done, it was a relief. Next up? Replastering the wall where the bed was, redoing that part of the floor, and building a wood bed frame…


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  • Just, wow. That is a massive bit of work. Congrats.

  • Wow, that looks like a LOT of work. But at least it is done now.

  • catastrophegirl

    maybe that was contributing to your dampness problem in the house as moisture leached outwards from the bed base.
    hopefully this will resolve some of that

  • Tom Meyers

    I discuss rocket heater technology in some of my building code seminars. I read your issues with your Rocket Stove with great interest today.

    I wonder if you are wicking water by capillary action from your damp soil. That would carry the water into the walls and your thermal mass bed. Water is an excellent heat storage medium. Might have simply stolen all the energy from your heater…at least what remained following your limited combustion. A lot of energy transfer to the surrounding soil and walls might never allow the building to heat to a comfortable level.

    The key to good combustion is to have sufficient draft. The small diameter horizontal flue and sharp bends will generate friction that will inhibit draft. The north wind probably induced suction at the flue termination that helped the system operate properly. The exterior vertical riser was too cold to induce draft via convection, so it was of no help.

    Lots of lessons to be learned by your experience. Sorry you had to go to so much effort for some gain in insight.

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