[GSBN] Tall walls and wet clay

Fri Apr 3 03:48:32 UTC 2009

Hi Laura,

We've tried processing local clay here in Ithaca (sounds like you may have already talked to Aaron). In our experience, it's possible but intensive, and how practical it is will depend on the type and especially quality of clay.

Our first straw bale (near Seattle) happened to be near a halfdug pond with subsoils at a perfect ratio of clay and sand. We just shoveled it in buckets, covered it with water, stirred it up a few days later with a paddle blade, screened it, mixed in some chopped straw and PRESTO - perfect plaster. 

Here in Ithaca, we're finding very pure clay deposits (nearly 100%). The consistency is generally between potter's clay and rock hard depending on seasonal moisture and exposure. We use a sledgehammer &/or pickaxe to break of movable chunks which we've tried processing both wet and dry.

Soaking method: the clay chunks need soaked for many days - even weeks. We've soaked it right in the mixer and run it every few days to break things up and keep the clay particles suspended in the water. Eventually you end up with a clay slip about the consistency of cream plus a lot of big chunks of clay remaining. We pour the slip through screens into buckets and allow it to settle then pour off some of the water to get a thicker consistency. We once tried adding sand to the mix hoping it would help speed up breaking down the chunks, but it didn't make much difference. While this wasn't too labor intensive, it did take quite awhile to amass any considerable quantity of clay for plaster.

Pulverizing method: the clay chunks need dried for many days - even weeks. We spread them on a tarp (with another at the ready in case of rain!) and roll them around every few days to dry them out as much as possible. Once they're pretty dry you can smash them into smaller pieces to dry more. When all the chunks are fist sized or smaller and completely dry, we run it through a chipper/shredder - a very loud, lengthy, and unbelievably dusty process. When you are done you will have a large amount of usable clay powder (though still containing small chunks that you don't find in bagged clay), a lungful of dust (no matter how good of a respirator you wore), and a chipper/shredder in need of a complete overhaul.

Some owner/builders still do this, but we've found it too impractical and have switched to bag clay. Sarah Highland may have had a little more luck with this.  I think she dries the clay and smashes it,and then soaks it - thus having smaller pieces to soak. Even so, much as we'd love to take advantage of this local material,  all of these methods are just too time-consuming and therefore costly. 

The industrial pugmill and papercrete mixer ideas sound intriguing. However, the pug mills I've seen are used to reconstitute clay scraps and might not be hardy enough to deal with stones and other impurities we run into. And based on our experience with the chipper/shredder - sending clay with any moisture through just leaves you with clumps and/or a gummed up machine. Sending it through dry would definitely pulverize the pile  faster than feeding it into a little chipper/shredder - but dang your gonna create one heck of a duststorm!

ej

p.s. Thanks for adding an NBNE representative to your list. We've all appreciated the insight, thoughts, and ideas we've gotten from Mark Piepkorn cross posting some of your threads to our group in the past.

------------------------------------------
ej George
Certified Sustainable Building Advisor
607-387-3602
ejgeorge at riseup.net

Quoting "Laura Bartels" <laura at greenweaverinc.com>:

>Hi Rikki,
>
>This clay is much more like modeling clay as you describe and  difficult to make into a slip. Drying may be the way to go here, which  is what we've discussed.
>
>Has anyone else worked with clay in large quantities in this way?
>
>Laura
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>Laura Bartels
>P.O. Box 912, Carbondale, CO 81623
>Ph 970-379-6779, Fax 970-963-0905
>laura at greenweaverinc.com
>www.greenweaverinc.com
>
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>On Apr 2, 2009, at 8:33 AM, Rikki Nitzkin wrote:
>
>>>>Laura Bartels:
>>
>>>On another project, an office building in PA, they have located  great clay, with little expansiveness, but when sourced, is very  wet and not easily processed.
>>
>>How wet is it? In Denmark the people have clay slip delivered  directly on sight. No dry clay is used. Personally, I prefer working  with "clay slip" (clay the consistency of a thick milkshake) to  using dry clay. If it is too thick you can add water and use a hand- held mortar mixer with a "paint" drill bit to thin it out a bit. If  it needs seiving it is easier to do the thinner the mix. This WILL  change the proportion of sand/straw added to the mix, so make some  tests and be sure to be consistent in the making of the clay slip.
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>>If it wet like modeling clay (humed but solid) it is too dry to mix  well and too wet to disolve easily, so it would be better to dry it  out and pulverize it.
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>>
>>Rikki Jennifer Nitzkin
>>
>>Self-builder, education and consultation Straw Bale building and  Earth Plaster
>>rikkinitzkin at earthlink.net
>>www.geocities.com/rnitzkin
>>0034 657 33 51 62
>>Aulás, Lerida (Spain)
>>
>>Coordinator Spanish Straw Bale Network
>>www.casasdepaja.org
>>casasdepaja at yahoo.es
>>
>>"We have the Right and Responsibility to Create the World we Want to  Live in"
>>
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