trying to find clay to buy that is reasonable priced is been a very difficult task around here....
so I started doing some research...I think that the cheapest unscented ground clay cat litter would do the trick? not talking about the bentonite clumping litter but natrual ground clay litter?
any body ever tried this or have any thoughts about this?
Anthony; What is your location ? Cat litter is not going to work well for you. Clay is found almost anywhere. Try talking to your county road crew they will know where they have a clay problem on a road cut, or talk to a local building contractor , they will no doubt have a foundation excavation loaded with clay. Fire clay in 50# sacks is available but shipping is cost prohibitive, so locating some and doing a road trip to acquire it may be an option. In spokane it costs roughly $10 a 50# sack.
I live in west central Minnesota, I am sure I could find some natural clay in the ground here, but was curios why ground clay cat litter will not work? its just clay? from my research?, when I dig clay from the ground do I need to clean it?
I understand some cat litter is partially fired so that it doesn't behave entirely like natural clay. Most of it also has perfumes or something that I probably wouldn't want in a building or heating appliance.
Whether you need to clean the clay depends entirely on your local source. Some places (Georgia) have clay you can dig out of the ground and use straight on a potter's wheel. Other places (my land) have clay that is about 50% gravel or rock, 30% sand and 20% clay. That actually turns out to be perfect for cob building once you remove the larger stones, but wouldn't work for many traditional clay uses.
Dig about 20kg of soil up and put it into a large round rubber tub.
Add at least 50 litres of water.
stir it for a few seconds with a garden spade.
Get the largest stones out the bottom of the tub to make more stirring easier.
Stir it for a few more minutes.
Scoop off the organic matter that is floating on the top. Stick it on your compost heap or directly on your growing areas.
Leave it to settle for a day.
sand and stones will settle to the bottom. Next layer is silt. The top layer of settled out material is clay.
So even if you only have 10% clay soil, this gets you 2kg of clay with just a few minutes of effort.
(20kg is roughly 44lb)
(50 litres is roughly 12.5 US gallons)
My guess would be that most cat litter contains bentonite - that's what they were excavating in the "kitty litter mines" when they found pleiosaur bones a while back.
And it's the easiest clay to make into those little nodules, because it shrinks and cracks readily when it's dried out.
The extreme shrinkage of bentonite is what makes it hard to work with. You have to soak it forever, the clay-slip holds so much water it's translucent, and then you need enough good-quality sand to hold against the terrible strain of that clay trying to shrink back down 20x smaller as it dries. Any of those little nodules that don't get thoroughly smeared out into the sand will want to start a crack as they shrink. Too much bentonite clay, and the project basically rips itself apart and turns back into slightly larger-scale kitty litter as it dries.
Minnesota has a lot of silty soils from the glaciers, but you should be able to find clay pockets.
You could certainly try making test bricks, if you are the "show-me" type. You could have a local kitty litter product that I haven't seen.
But "fire clay," mortar clay, or hobby-potters' discarded raw clay are not that hard to find, and they will most likely give you better return on time and money spent.
Community colleges and ceramics studios are often quite willing to let go of large bins of "recycle clay" for a good cause. (Anything that does not involve paying the art teacher overtime to process porcelain, terra-cotta, stoneware, and miscellaneous discarded tools and bisqueware into a usable, kiln-tested home blend may be considered a "good cause." Bring your own bins. They mostly save out the "recycle clay" to protect the sink drains, re-using the clay for pottery is often a lost cause unless the students are REALLY well trained to grade and separate. But it's great for building projects. Potters who throw on a wheel often have tons of spun-off and trimmings that are likewise mixed and hardened, useless to them, gold for your project.)
If using pure clay, you will only need 6% to 15% of the project's final weight. Depends on the clay, depends on the rest of what's in it (surface areas, etc). But you can make a couple of tote-bins of recycle pottery clay go a long way, sometimes we add less than a half-gallon to each batch, with 3 buckets sand and one bucket of the most "clay-ey" soil you can find locally. (4-5 gallons is a bucket by my measure).
Hope that helps.
If that's not enough "why," then definitely try it and see.
Mix several different proportions with sand, very well. Make bricks using a form (could be a planting pot, filled level to the top) so you can compare before and after to measure drying shrinkage.
There's more detail in the 'mud guide' on our Kickstarter, or in Appendix 1 of our new book (see signature), or in cob builder's handbook (becky bee), or cob cottage company has several titles with general info.