DIY clay growing media firing clay

There are many types of clay growing media out there such as turface or hydroton, used for potting soil and aquaponics. They give a mix the clay advantages of high cation exchange capacity and water holding ability, while avoiding a sticky pudding or brick. They are inert and long lasting.

I'm wondering if one couldn't make the stuff on a small scale locally. I'm not sure how exactly it is made so that it is porous, but I know it involves pretty high temperatures.

I've got two ideas:

1. For small scale testing of recipes and temperatures, would a microwave kiln work? These are small inserts that go inside a standard microwave for making glass or ceramic ornaments.

2. For large scale production, what if a rocket J tube was made of clay, perhaps with straw or sawdust mixed in, and let to dry. Then it could be wrapped in rock wool insulation and fired. I imagine that it would not hold up too well, but before it fell apart, would the clay have turned into something like the desired product? Any organic matter would have turned into biochar, which is a good potting mix ingredient on its own right.

Any other ideas on how to achieve this? The background is that I'm trying to start a permaculture nursery which would use all recycled or locally sourced materials, and I've got a giant pile of clay subsoil in the back yard.

Or could I coat the inside of a brick rocket J tube with my mixture to be fired?

Depending on your definition of "local", you might consider using cinders from Dotsero Volcano. I bet that simple accounting would show that it requires less fuel to import cinders than it would to fire clay.

(Edit to add: OK, I did the math. It takes about a gallon of fuel to import a ton of cinders from the volcano. It would take more than 30 gallons of fuel to fire a ton of clay.)

I think that there are three coal burning power plants in the Denver metropolitan area. Perhaps you could acquire cinders from them.

Is there commercial mining of cinders there? I wonder how they would work.

I guess we would have to factor in the impact of cinder mining on the local environment. Also, of course, the clay idea may be impractical, in which case it is a moot point.

Gilbert Fritz wrote:I guess we would have to factor in the impact of cinder mining on the local environment.

While considering externalities, I hope that you consider the environmental impact of mining clay.

I bet that if you visit the stone yard of the company that supplies your local landscapers, that they will have cinders from the volcano. Around here, they often come screened to "pea-gravel" size, which is about 1/4".

When I consider externalities, I often find that doing things myself requires more energy than using materials that are acquired in bulk in far away places... For example. On a per pound basis, it takes more fuel for me to take vegetables 10 miles to market in my pickup than it does to bring them 1200 miles from California on a semi.

The externality question is an interesting one; I've heard in a similar way that rising lamb in New Zealand and flying it to England is more environmentally friendly then raising it in England.

But I'll have to open another thread on this.

As for the clay soil, clay is "mined" in the already heavily modified environment of the Denver metro area as a result of building construction. But if it was done on a large scale, then I guess yes it would be damaging.

On the other hand, if I fired the clay with carbon neutral wood (planting enough trees to take up CO2) then that would be better then burning oil to transport cinders.

I'm also wondering about crushed bricks.