[Greenbuilding] [SB-r-us] Re:Crushing Clay

[Bill]

First of all I plead sanity to Rob Tom's suggestion that I've used a hammer mill to crush clay.
I think moving to a more ideal place to live that supported other methods would be easier and preferable.
As for how to deal with such a creature, I've found that the easiest way, at least for us, was to soak the clay in water and let it break down.
Some do this easier than others and yes, there are some that really resist dissolving.

But let's start with those that do.  Couple of things we've done include building a a rectangular pit from straw bales on pallets, lining it with a canvas or porous tarp and putting the clay and water into this container.  Once soft, the clay can be mixed more thoroughly with the water, ideally completely and then what will happen is that the heavier aggregates will fall to the bottom and the clay layer will be on top and easy to separate.  It's a little time consuming, but not out of the question if the clay will dissolve.

If the hardened pieces of clay resist the method above one typically has to resort to some sort of mechanical crushing whether manually or by some sort of device.  The best thing I've seen that made sense to me and is the route I would go if I had enough use for, is a crusher that I saw in Denmark a couple of years ago.  It was made by a guy from Holland who produces vertical shaft mixers, various types of machines for compressed soil blocks and a machine that resembles a vertical shaft mixer and does a beautiful job of reducing hardened clay chunks to a powder.  It was relatively small, portable and I think the cost of buying and getting one here could be justified depending upon the quality of work one did with clay.

We've also encountered different situations such as when we were in Nova Scotia, we were delivered clay that was free of aggregates of any sort and that came in dense blocks, still moist, not unlike what would purchase from a ceramic supplier for making pottery.  There what worked best and gets into the the techniques Rob Tom described, was to peel off slivers with a shovel, throw them into a mortar mixer and add a small amount of sand with water to get the clay dissolved.

In short, there's a lot of variation when it comes to clay, the forms it comes in and how to get it mixed to the right consistency for the work being done.  My solution for places as in the above, short of moving west and south, find a brick factory and purchase their crushed and dry clay if possible.  Just did that in Denver and will do it next year in Minnesota.

Bill


On Aug 3, 2011, at 3:53 PM, RT wrote:

> On Wed, 03 Aug 2011 16:55:44 -0400, natural building  
> <naturalbuilding at shaw.ca> wrote:
> 
>> tried the "dissolve-all-of-the-clay-to-make-a-minimally-wet-clay-slip"  
>> approach at a fairly early stage in the process but it was totally  
>> unworkable.
> 
>> The ratio of water to clay necessary to achieve the optimum Proctor 
>> (compressive strength) is in the region of 30 - 35% by weight (water to  
>> clay)and resulted in a ridiculously sticky mixture that was impossible  
>> to thencombine evenly with the aggregate.It just turns into a large ball  
>> covered in gravel.
> 
> The "minimally-wet" stipulation mentioned earlier was intended as an  
> attempt to address the issue of excessive shrinkage (and possibly  
> shrinkage cracking) after the mixture has been placed in the forms.
> 
> However, I don't think that for clay mixes, there is any issue similar to  
> the critical water:cement ratio that affects the strength of the final  
> product as would be the case for concrete where the water is apportioned  
> like a chemical formula for hydration of the cement.
> ie I don't think that there are any chemical changes going on in the clay.  
> Molecular structure changes perhaps.
> 
> That is to say, I strongly suspect that one could make a soupier clay slip  
> than would be implied by the 30-35% water: clay ratio you mention (for  
> ultimate compressive strength).
> 
> ie Perhaps one makes the slip as soupy as is required to facilitate  
> reasonable workability and then set the mud aside (perhaps covered if  
> necessary to control moisture loss rate) to let it dry out to the desired  
> moisture content to reach the 30-35% water: clay ratio  (maybe days, maybe  
> weeks "curing" time) before placing in the forms for tamping ?
> 
> The term "unworkable" is pretty subjective too.
> 
> ie One of the most common mistakes that novices make when mixing  
> cementitious mortars without the aid of a mechanical mixer is that they  
> don't do enough mixing of the properly-proportioned mix and finding that  
> it's too difficult to work with, add water to the mix to make mixing  
> easier when in fact, what they should have done is mix longer with more  
> elbow grease.
> 
> I know that a clay soil that seems fairly dry and hard and not amenable to  
> being worked, will eventually turn into a pliable and plastic material  
> when "kneaded" with sufficient (very high) pressure, not unlike what  
> happens during the floating and trowelling processes in concrete finishing  
> ... a process of compaction that amongst other things, brings water to the  
> surface.
> 
> I'm wondering if the unworkable, large, gravel-covered ball you mention  
> was worked only by hand or were mechanical means tried as well ? (Like  
> maybe something similar to an institutional-sized bread dough mixer ... or  
> a herd of cows  ... or [ ] ?)
> 
> 
> 
> 
> -- 
> === * ===
> Rob Tom
> Kanata, Ontario, Canada
> < A r c h i L o g i c  at  Y a h o o  dot  c a >
> manually winnow the chaff from my edress if you hit "reply"
> 
> 
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