<p>One part of my garden has a heavy, dark clay soil. It is now waterlogged with a lot of surface water that does not shift at all even after a day of waiting. When pressed into a 4mm thick ribbon, it breaks under its own weight after about 10 or 15cm. </p>

<p>I do not have a photo to hand, but may try to upload later.</p>

<p>I took a large handful of the material and compressed into a ball. I rolled it around until smooth and left it on my outside windowsill to dry. When I came back to it late the next day, it was completely solid, like a little cannon ball. It is not quite as heavy as an iron ball, but it has that same dark faded metallic grey iron colour, though much less metallic, more like slightly reflective but matt. Knocking it on the wall, it doesn't flake, chip or crack. It's solid as a stone.</p>

<p>Is this normal for clay? I was under the impression it needed to be fired to become solid like that. The reason I ask is I have a partly demolished wall that I would like to restore, and I am thinking that perhaps I could just excavate this area of the garden to use as a building material, rather than try to solve my drainage problem. If this is not normal for clay, how could I identify what it might be, and if/how to use it as a building material? If I can make a cob from this, would that be suitable for an outdoor wall?</p>

CC BY-SA 4.0
2020-06-10T07:27:15.900Z
You don't need to fire mudbricks, they have been used to build for more than 10,000 years with just sun drying. See adobe for instance, or rammed earth: https://en.wikipedia.org/wiki/Adobe
Jean-Marie Prival
CC BY-SA 4.0
2020-06-10T07:50:57.093Z
@Jean-MariePrival Yes, cob is like adobe, but it requires the addition of sand and fiber for tensile strength. As far as I understand it, it is rain proof. Though I cannot understand why cob would be rainproof and dried clay not.
Frank
CC BY-SA 4.0
2020-06-10T07:55:27.000Z
@Jean-MariePrival Hmm. Apparently cob needs some sealant. I think I might be wrong about cob properties in water.
Frank
CC BY-SA 4.0
2020-06-10T09:07:16.970Z
this might shed some light on this topic https://en.wikipedia.org/wiki/Clay it is about the properties  and uses of clay.
trond hansen
CC BY-SA 4.0
2020-06-15T18:47:58.417Z
It could just be a very dense clay, but there are some stranger natural soils. Plinthites can alter irreversibly from workable to permanently indurated when they dry out. I'd wait a month or so and then put it in a bucket and see if it softens. Can you look up a soil survey for where you are to give us a hint what kind of clays you have?
cphlewis
CC BY-SA 4.0
2020-06-15T20:26:46.647Z
@cphlewis That's very interesting! Well since posting this question, my Mrs has discovered the same properties and has joyfully launched herself into lining various baking tins and wotnot with baking paper, stuffing this clay substance into them, and hollowing them out into various potential items of crockery. We shall see in a month, as either there will be a heartbroken husband with a house full of malformed pots, or a heartbroken wife with a broken top of the range Siemens dishwasher choking on soapy mud. Soil maps for around here exist, but my garden clay is in one area and not another!
Frank
CC BY-SA 4.0
2020-06-15T20:31:17.157Z
@cphlewis I am told by locals that in bygone days there was a brick factory here. Oddly though, a few hundred metres away, is a retired peat 'factory' and a large area of peat. My clay is very dark and doesn't give an indication of containing much fibrous matter, but it stinks to high heaven, probably because of the surface waterlogging. I will research tomorrow and post what information I can unearth.
Frank
CC BY-SA 4.0
2020-06-16T00:34:24.053Z
Some firing clays appear as strata directly under strata of coal or soft coal. Not too strange to have them near other materials.  If there was a brick factory, I think you should try firing them... and water-test the crockery outside!  Cob, in wet places, needs a `hat and boots' of roof and rocky foundation, it isn't itself waterproof.
cphlewis
<soil>
Is it normal for clay soil to solidify into a very hard, but not brittle, material in air, and if not what might this soil be?
Frank
# Is it normal for clay soil to solidify into a very hard, but not brittle, material in air, and if not what might this soil be?

(Asked by: username_0 on 2020-06-10)

One part of my garden has a heavy, dark clay soil. It is now waterlogged with a lot of surface water that does not shift at all even after a day of waiting. When pressed into a 4mm thick ribbon, it breaks under its own weight after about 10 or 15cm.

I do not have a photo to hand, but may try to upload later.

I took a large handful of the material and compressed into a ball. I rolled it around until smooth and left it on my outside windowsill to dry. When I came back to it late the next day, it was completely solid, like a little cannon ball. It is not quite as heavy as an iron ball, but it has that same dark faded metallic grey iron colour, though much less metallic, more like slightly reflective but matt. Knocking it on the wall, it doesn't flake, chip or crack. It's solid as a stone.

Is this normal for clay? I was under the impression it needed to be fired to become solid like that. The reason I ask is I have a partly demolished wall that I would like to restore, and I am thinking that perhaps I could just excavate this area of the garden to use as a building material, rather than try to solve my drainage problem. If this is not normal for clay, how could I identify what it might be, and if/how to use it as a building material? If I can make a cob from this, would that be suitable for an outdoor wall?

**Tags:** soil

> **Comments:**
> **username_1**: You don't need to fire mudbricks, they have been used to build for more than 10,000 years with just sun drying. See adobe for instance, or rammed earth: https://en.wikipedia.org/wiki/Adobe  
> **username_0**: @username_1 Yes, cob is like adobe, but it requires the addition of sand and fiber for tensile strength. As far as I understand it, it is rain proof. Though I cannot understand why cob would be rainproof and dried clay not.  
> **username_0**: @username_1 Hmm. Apparently cob needs some sealant. I think I might be wrong about cob properties in water.  
> **username_2**: this might shed some light on this topic https://en.wikipedia.org/wiki/Clay it is about the properties  and uses of clay.  
> **username_3**: It could just be a very dense clay, but there are some stranger natural soils. Plinthites can alter irreversibly from workable to permanently indurated when they dry out. I'd wait a month or so and then put it in a bucket and see if it softens. Can you look up a soil survey for where you are to give us a hint what kind of clays you have?  
> **username_0**: @username_3 That's very interesting! Well since posting this question, my Mrs has discovered the same properties and has joyfully launched herself into lining various baking tins and wotnot with baking paper, stuffing this clay substance into them, and hollowing them out into various potential items of crockery. We shall see in a month, as either there will be a heartbroken husband with a house full of malformed pots, or a heartbroken wife with a broken top of the range Siemens dishwasher choking on soapy mud. Soil maps for around here exist, but my garden clay is in one area and not another!  
> **username_0**: @username_3 I am told by locals that in bygone days there was a brick factory here. Oddly though, a few hundred metres away, is a retired peat 'factory' and a large area of peat. My clay is very dark and doesn't give an indication of containing much fibrous matter, but it stinks to high heaven, probably because of the surface waterlogging. I will research tomorrow and post what information I can unearth.  
> **username_3**: Some firing clays appear as strata directly under strata of coal or soft coal. Not too strange to have them near other materials.  If there was a brick factory, I think you should try firing them... and water-test the crockery outside!  Cob, in wet places, needs a `hat and boots' of roof and rocky foundation, it isn't itself waterproof.  

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## 0 answers

