[Greenbuilding] Crushing Clay

[natural building]

Chris, I've found (through more than a year of testing) that rammed earth is a very different beast from earthen plasters or LSC. the amount of water necessary to obtain maximum strength is considerably lower than for plasters, etc. where strength is not the issue. The clay content of the mix needs to be 'just' wet enough to activate the ionic bond between the clay particles. At this point it is at its most 'sticky'. Any more water and the clay particles start to flow. While this might make it more 'workable' it also weakens it.

The need to hydrate the clay with 'exactly' the right amount of water is critical. As I mentioned in a previous post, controlling shrinkage is absolutely key to obtaining adequate strength and the margins are very tight.

In order to properly hydrate the clay with just the right amount of water, it is important to reduce the clay to the smallest particle size that is practical. Other wise the moisture does not penetrate to each clay platelet and consequently you do not activate the ionic bond between the platelets. This is critical.

For those who are less familiar with clay, the LARGEST clay particles are 0.002 mm in size. So a lump of 1/8th" can be made up of, literally, 1000's of particles.

I'm not sure if I've explained that very well, but suffice to say that if the lumps of clay are too big the water doesn't adequately penetrate during mixing (mortar/stucco mixers which knead the clay do a better job at this). Trying to  compensate with more water causes too much shrinkage which, obviously, weakens the final assembly.

Inspired by some of the suggestion on this site, I have come up with an idea for a crusher which involves using a horizontally mounted drum of about 3 feet in diameter by 2 feet in length, enclosed at either end, within which would be a smaller heavy drum of maybe 8 - 9" by slightly less than 2 feet in length.

The idea being that as the outer drum rotates, the smaller heavy drum inside will crush the clay passing under it.
Still in the 'concept' stage and I can see the potential danger that the smaller drum might twist and lock within the larger drum...

Any thoughts on this folks?

Regards,
Steve Satow

www.naturalbuildingsite.net
naturalbuilding at shaw.ca

On 2011-08-05, at 6:12 PM, Chris Koehn wrote:

> 
> Steve,
> 
> I just finished work on a straw clay structure on Salt Spring Island, BC. Technique there was to screen the clay, using manual pressure against a chicken wire screen. The resulting 1/2" minus went straight in to a mortar mixer (which is different than a cement mixer) with water. The paddles seemed to do an efficient job of creating slip quickly (15-ish minutes), 4 to 7 gallons per batch.
> 
> Chris Koehn
> TimberGuides Design • Build
> Van Isle BC
> 
> Steve wrote: .."I wonder if I can tap into your collective intelligence and  
>> ingenuity to come up with a simple, cheep, mechanical system for  
>> crushing dry clay into a coarse powder..."
> 
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