Old 07-25-2011, 06:03 PM
Master Builder
Join Date: May 2011
Location: South Australia
Posts: 621
Default Clay

While out walking the other morning, I came across an outcropping of something I thought was clay, a very light grey coloured mud. When I kicked it, it was very solid, but slicker than wet duck sh*t.
So I broke a little piece off and took it home. It passed the "roll it out and wrap it around your finger" test without breaking, so I shaped it into a small bowl and left it on a fence post to dry. That afternoon it looked fully dried (it was only about 1/4 inch thick). It kinda "rang" when I tapped it with a fingernail.
So, I took it inside, made sure the misssus was safely tucked up in front the TV and unlikely to notice what I was doing with her stove, and fired up a burner on the gas stove. I heated this thing in the gas flame so it was glowing red - which I reckon is about 700 degrees centigrade.
I kept turning it over in the flame, getting as much of it to glow red as I could, then let it cool down.
I ended up with a light pink terracotta bowl. Reckon I found me some decent clay - so last night I did a commando raid with a shovel and a bag.
I have made a start on processing it by mixing it to a slurry with a paddle in an electric drill, and pouring the slip through a screen. Not much in the way of sticks and leaves, and very little sand and rocks being left behind either.

I've done a bit of research, and it appears the defining characteristic of fire clay is a very high melting point. This stuff can be heated to glowing red without even looking like softening, it still "rings" when tapped even when its red hot.
Next step is to mix up a small batch of the homebrew refractory mortar using this clay and see how it goes sticking a couple of bricks together. Then chuck it in a fire for a few hours and see what happens.
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Old 07-26-2011, 02:25 AM
david s's Avatar
Il Pizzaiolo
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 5,157
Default Re: Clay

At the temps we fire to any clay should suffice. Processing your own is fun but quite a lot of work.
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Old 07-26-2011, 03:22 PM
Master Builder
Join Date: May 2011
Location: South Australia
Posts: 621
Default Re: Clay

You are right about the amount of work Right now there are 3 bags of slurried up clay hanging in my shed dripping water. Not much rubbish came out when I mixed it all up. A few dead bugs, almost no tree roots, twigs, rocks etc. Might just about have been able to use it without processing. When I get it all in bags I'll hang it under the carport ion the breeze to speed things up.
I reckon that by the time I come to use it, it will be dry. I have to make my stand first, etc.
My plan is to crush and sieve the dried clay, mix up the 3:1:1:1 sand:cement:clay:lime mix dry, then add water at the last. My reading suggests that trying to use wet clay results in a balled up mess?
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