Ideas for pulverizing hard clay dirt

Do you have any ideas for pulverizing clay dirt?  I’ll be working on the walls of my cob house this summer (yeay!) and I’ll need to “process” a lot of clay soil. Ideally I want to break the clay into a relatively fine powder so the sifting and mixing is easier. 

Even though the clay is somewhat broken up when it’s delivered, there are still many small to large clumps, up to 12”, of hardened clay.  I don’t have any heavy machinery so I’m looking for creative and efficient ways to get the clay ready for mixing.  Last year I used a car to drive back and forth over bags of soil.  It broke down some of the lumps but it wasn’t a good process for large amounts of soil.  Thanks for any ideas!

I've reduced material with a cement mixer and some round rocks, about fist size. You have to remove the paddles inside the mixer. Sounds like you need something larger though.

Roto-tiller? (spelling..)

Jeff

Jeff,

The cement mixer sounds workable.  I'd hoped to avoid renting major machinery but I've got to use my time there efficiently.  Did you also use the mixer to make your cob mix?

As for the tiller, I can borrow one of those.  I'm thinking, create a big pit, throw in the clay and use the tiller to crumble the clay.

Thanks for two great ideas!

This one is slow but will work if the clay is coming from the field.

Step 1
Plant root crops: turnip, carrot, radish, daikon, beets, rutabaga, maybe some peanuts and potatoes for good measure.  Mulch with hay.

Step 2
put up a fence

Step 3
Get yourself a pig

The growing plants will break up the clay soil some.  The pig will dig up the roots as it forages for a sammich.  The mulch helps to retain moisture, slowing the development of hardpan.  Some of the hay will get mixed in as the pig does his thing.

Do you have a couple of years?

BALL MILL
To the cement mixer, add some 2" steel balls.  As the machine turns, the balls will roll and thunk around, smashing the clay into dust.  Same idea as the round rocks mentioned by puffergas.  If steel balls or rocks are not available, bricks may get you by, but they will be destroyed over time.

SCREENING
Run the tiller, shovel up the loose clay, run it through a ball mill.  When the stuff is pulverized sufficiently, run the material through a screen to sift out the small powder.  Put the coarse material back in with the next batch.  1/4" construction fabric would be durable enough to do the job on the scale you are involved with.

WET/DRY
Sloppy idea, and lots of hard work.  Water down an area where the clay is coming from or dumped.  Work the clay into a slurry with the tiller.  Shovel this mess onto some visqueen.  The trick is that it be wet and runny enough to level out.  When dried in the sun you would have a thin layer which should break up as you pull up the plastic.  The result is smaller pieces to put into the mixer/ball mill.  Wear rubber boots.

PERCUSSION
This method involves the use of a sledgehammer or pickaxe for those 12" clods.

My ex-father-in-law was a potter, so I've watched him work with clay quite a bit.  If the clay is coming in hard, dry lumps, the best way to be able to work other substances into it is to moisten the clay into a slurry -- don't get it any wetter than really necessary because the more water, the longer it will take to dry out to where you can work with it.  You'll still have to do some breaking up of lumps manually, but should be able to get by without renting a cement mixer.  Just start each day's batch of clay a day or two (or three -- experiment and see how long it takes to dry to the right consistency) ahead of time.

Kathleen

my thought would be to wet it also.  If you can sift it through a large screen then throw the chunks into a big garbage can and ad just enough water to saturate it.  Once it is moistened the clumps are easy to break down.

I'm planning on using a cement mixer for making my cob.  I've done it in a commercial hobart mixer but it is small for housing only makes a couple of gallons worth at one time, but does make the mix remarkably smooth (I actually used it to mix paper clay before cob experiments) 

I got a gas cement mixer on a sort of close out, handles a couple of bags of ready mix and does a nice job, and I've seen a variety of them rigged for cob.  It was about 350.00 which is a lot of $$ but if it works as well as I think it will save hundreds of hours.

There is also someone building with cob that basically throws everything onto the ground and drives back and forth over it with a tractor and then uses it, word is it works great, seems to me would be best if there were a number of folks cos it would get rather spread out, and have to be scrapped together, but I'm guessing on that.

Ken:
I love the pulverizing idea that involves having a pig forage for sammiches ...but I do want to complete this cob house on a faster schedule than that.  I will keep that process in mind for rehabbing the field though.  The land where my house sits is in very poor shape (packed clay soil where little grows but wild cedar and carpetweed) and I have visions of helping the soil recover its fertility and vitality.

Re your other suggestions, the ball mill and the tiller are my likely options.  I tried the slurry thing but even after an overnight soak those big clay clods don't break down without a fight!  Bad news for my back, good news for the cob house!

Kathleen: I tried the soaking/slurry method and it worked fine but only if I used well powdered clay.

Serenity: thanks for the info on the cement mixer.  I'll keep my eyes open for a used one and compare that to the option of renting.  What do you mean by having the mixer "rigged for cob"?

I used the cement mixer/balls to grind up charcoal and to pulp retted weeds. Yes this is a ball mill. Kind of hard to find round rocks so SOMEDAY I plan on trying to make them from cement formed with my hands. Kind of like making meat balls but a bit larger.

I never used a tiller for anything so best ask someone that uses one how they think it might work.

One more thought on the cement mixer; you could buy a used one then sell it when your done. Hard for me to believe that a small mixer could produce enough clay for a house but maybe it's just used as a coating, I don't know anything much about cob houses.


Jeff

Oh, I forgot. Another scheme to the cement mixer would be to use a 55 gallon drum layed down on four caster like wheels. Next you would need to decide how to turn the drum. Maybe a V-belt around the drum to a motor or turn two of the wheels. If the clay would break down fast hand turning MIGHT be an option..........

Maybe the drum would get dented up and not turn on the wheels.....

Jeff

puffergas wrote:
Oh, I forgot. Another scheme to the cement mixer would be to use a 55 gallon drum layed down on four caster like wheels. Next you would need to decide how to turn the drum. Maybe a V-belt around the drum to a motor or turn two of the wheels. If the clay would break down fast hand turning MIGHT be an option..........

Maybe the drum would get dented up and not turn on the wheels.....

Jeff

What about one of the drum compost tumblers?  I've never examined one closely, so don't know if they are sturdy enough, but it might be a possibility.

Kathleen

More options...

For a pile of clay dumped on the ground, spreading it out, then running over it with a harrow can handle most of the bigger lumps.  A means of towing the harrow would require a tractor with a 3 point hitch or put a 2" ball hitch on the thing somehow.

In lieu of a harrow and tractor, a chain link fence can be dragged behind a truck or car repeatedly. This will take longer than a harrow which is considerably heavier.  Placing some large rocks/blocks/clay clods on top of the chain link may give you some advantage.  You will need lots of turning room otherwise you have to unhook, drive around, hook back up for each return trip.

Seems to me the biggest obstacle is getting the big chunks down to a managable size.  I'm thinking for the money, a pickaxe may be your best bet.  The bigger the chunk, the fewer.  A few swings breaks up a big one to a size it can be loaded into the mixer.  With the issue of the biggest out of the way, you can put your attention to getting the stuff down to what you need for construction.

Kathleen Sanderson wrote:
What about one of the drum compost tumblers?  I've never examined one closely, so don't know if they are sturdy enough, but it might be a possibility.

Kathleen

I don't know Kathleen, I never use one before. It would have to take some beating from the rocks/balls.


Jeff

In theory, rolling is the most efficient way. This theory only holds when the rollers are large enough and held at the appropriate gap stiffly enough, but it's possible that if you raked an even layer of dry chunks onto some pavement, and took a lawn roller to them, you would make some headway without too much extra work.