Electric Mixer Cob

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Cob takes a tremendous amount of human energy to create. A batch might take an experienced cobber 15 – 20 minutes. It takes me a little longer, since I have to bring materials from 200 feet plus to the site.
Now that I’ve moved some 50 tons of material I decided that I need a worker bee!

First Impression

Since I can’t really afford to pay people what they are worth I, and workshops are even more work, I purchased a electric mixer.

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The IMER, Wheelman,110v Electric Mixer – made in Italy.
http://www.imerusa.com/
What I liked about this model is that it has wheels, so you can roll it around and pour it out where you want it. This is particularly wonderful for me since I don’t have a hose to clean it on site. It’s quite, and well built. At around $400.00 USD it’s an investment, but one I hope that will return many times over.
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Other cobbers have said that they like the mortar mixers better because it squashes the clay chunks better. Mortar mixers have an apparatus inside the barrel that turns, while cement mixers turn the barrel it self. Since mortar mixers are quite a bit more expensive I went with the cement mixer. It’s worth a try -right?

Now, will it work for making cob?
At first I wasn’t sure. I started with water, then added clay to the mix. I tried hard to scrape the clay off the pile, as to avoid big chunks. Then sand. It seemed like I had to add a lot more water to get it to mix, otherwise it just kinda sticks to the sides. More water.
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While the mixer is turning, I can go gather the next batch of sand, clay and water. After about 10 minutes of mixing the cake batter like mud is ready to pour out. It comes out pretty easy, but it definitely wants to hold on to the insides of the mixer. A hoe can get the rest out.

This mix is very wet for traditional cob. However, I am a fan of mixing cob wet and then letting it sit around for a while. It’s always easier to get the straw throughly mixed in with wet cob. Straw also seems to absorb a fair bit of the moisture.

I dump the mix on a tarp and add the straw by hand & foot. This allows me to go after any rogue clay chunks that still exist in the mix. I didn’t have to mix it too much before it was ready to go. Now it’s time to make some cobs and set them aside to ‘cure’ or dry. After a few hours they are in perfect condition. Moist, tough, malleable, and solid. You can pick the cob up and it all holds together.
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After working with the Wheelman one full day I was pretty sure that the investment was worth it. Instead of acting as a human stomping machine, I can save some of my energy for gathering the ingredients and applying the cob to wall. Hopefully it will be worth the added steps of adding material to the mixer, taking it out, then stomping it. Cleaning the mixer after every use is an added activity. I wonder how it will impact the electricity bill.
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Overall I’m in favor or the electric mixer. It has turned my one-man-band into a one and a half man band. I need all the help I can get. This cob stuff doesn’t mix itself and jump on the walls – though that’s what I’m working on next…

Second Impression

( Updated august 6th 2005 )

I think it helps when the clay gets a little rain. It makes it softer and not so hard.
Today I tried mixing the clay and the sand together dry and then added water.
I was mixing 2 5 gallon sand and 2 5 gallon clay rich soil. The clay has some sand in it. It was a pretty good mix.
Sandy, but held together. I was able to add less water this way. It amazing how a little water can be just enough to keep it moving.

Well. I think that’s the prefered method. Add dry, let tumble, add water – just enough and presto. Mixer cob.
After it sits around for a while in partial shade and 72 degree weather it dries out to a prefect consistency.


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5 Responses

  • lynda says:

    thinking of using cob along with recyled bottles, jars and pine logs for low impact construction in Central Portugal. (high humidity, lots of autumn/spring rain and high summer temps) I came across this site whilst resarching cob, thanks an invaluable resource.

  • Michael says:

    Hey Cobhobo!
    Ya I got mine at an ACE hardware / Rental Store.
    Multi-tasking is overrated, but when your a one-man-band you take any help you can get.

  • cobhobo says:

    Can you buy these in North America? I enjoy getting my feet muddy, but it is nice to work on other jobs while the cob is mixing. This is excellent news…actually…cobtacular!!!

  • cfriend says:

    I’m glad to hear it works. Also…I volunteer to be a worker bee as needed…

  • Arthur Org says:

    I’m all for the electric mixer, too. I agree with your handling of the rogue clay chunk problem, it sounds like you have found a creative solution. I enjoy the site. Keep up the good work!