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What kind of clay am I digging up

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Ok I have a project I am doing a my home...digging out the crawlspace under the house... Yeah

I have tested the soil by mising it with water and letting it settle our after doing so I found that it is about 5% sand 94+% clay and silt was negligible.

I am at this point completely trashing all of this  by bringing it to the dump, giving it away, etc.

I also have a furnace for melting metal and was wondering if and how I could use this for molds.

The consistency of the clay I am digging is three basic layers. Out of 18 inches I am digging it is made up of about 5 inches of dry cracked material at the top, about 5 moist and very sticky, and the rest very wet and sticky as well. There is almost no rocks or plant material that I can see in the material.

I am hopeful I will be able to use some of this material with minimal processing because I have about 65 cubic yards of it. So far I have gotten rid of about 15000 pounds of it and am about 25% done with the job.

The strength of the material is as follows the top hard and crumbly. the middle breaks apart in large chunks and generally sticks together in larger pieces. The bottom level is very wet and seems to stick together BUT if I pick it up it seems to shear off and the ends of my hand so if I grab it in the middle it will break on both sides of where I am holding it. 

The lowest level when I actually dig it up it does seems to shear in places meaning it simply seems that a section breaks free and slides right of the original piece leaving a very clean break.

The main question I have is this: Is any of this usable as it or would it require a lot of manipulation in order to use it for molds?

Other questions I have are as follows:

What are the technical terms I should be using to describe the clay under my house.

Does processing this clay mean I have to add water and filter and then dry to a specific moisture level

What is the process I need to go through to make a clay mold from this material and which of the types would be the best to actually try it as is?

Thank you for your time


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No not yet I do not know which level to use the clay from and how long it needs to be dried and then how do I fire it. I am leterally just beginning and know absolutely nothing about how to use clay to make permanent molds for pouring metal.

I am a DIY person. I built a small furnace and have made ingots of copper and aluminum and my next thing is to make a bronze out of aluminum and copper and then make rings from that thus the needs for molds. I was just hoping I could at use least some of this clay.

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Test all three levels.  Form marble sized balls of each.  Make sure they are bone dry and dry them in the oven (slowly) for an hour or so at 105 degrees Celsius to be sure they really dry.    Just fire marble sized balls of each in some kind of container in the kiln to the hottest temp you guy.  Note if they melt or not

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To be technical, you need something that is "refractory".  That is, it doesn't melt.  Purchased clays are almost always blended to give different properties.  Unfortunately for you, your clay is unlikely to be refractory, so when testing make sure you put it in a waster-bowl so that if it does melt it won't ruin your shelves.

I dug some clay from my garden and from the local scout camp and tested it to 1,000C and it held up fine, but I haven't got round to trying it any hotter.

Good luck, and let us know how your tests go.

Edited by Chilly
missing word !

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