Need help understanding what clay I should buy to use in cob.

Hello,
Thank you for taking a look at my question.

I have done enough reading to understand that most people don't need the answer to this question. Because they use what they have. Simple enough.

My situation is not as simple.
I live in north idaho and have not found any clay bearing earth. I have a very small amount of soil, on top of sand and gravel. This sand gravel mix goes down more than 4 feet.

I have all the sand and aggregate I could hope for.

I want to buy clay to make cob, this is possible because the project is not so big as to make buying the clay a problem.
I have my pick, and I see many choices.


So my particular question is this:
Is there any clay I should NOT use?


I am new to this so feel free to offer any advise but I particularly want to know the answer to the above question.

-Josiah

Hi Josiah;
#50 sacks of dry Lincoln 60 fireclay are available in Spokane, WA  at White Block Masonry Supply on Trent Ave.
It was $12 a sack the last time I bought there.
In Missoula, it is $7.50 a sack at Mutual Materials.

You certainly do not need fire clay, but there is no reason not to use it.
It sure is cheap enough.

Thank you Thomas. That sounds cheaper than what I have seen so far. I like the price!

How far north are you?  Bonners ferry?
Sandpoint is famous for its blue clay
I'm 28 miles over the border in Western Montana and I can dig clay out of my driveway (if it wasn't frozen)

I am between sandpoint and CDA. A place called carywood.

I know there must be clay here, but I have not seen it yet.
Its good to know sandpoint is known for it.

I came here expecting to see clay and earth like other places I have lived along the west coast. But was surprised to find we live on absolute mountains of granite sand and gravel! It is unlike anything I have seen till now.

Do you have similar earth there? As I understand it this sand and gravel was produced by flood waters that might have originated in Montana and swept all the way down to the Oregon coast where I used to live. (the bandon dunes area)

Sure I know where Carywood is located.
Where I live is the Clark Fork Valley, east of Lake Ponderay also known as Lake Pend Oreille.
The ClarkFork Valley is where the Glacial Lake Missoula broke its ice dam (three times) and released all the stones and gravel that passed through north Idaho on its way to the Columbia River basin.  
So some spots in the West slope have lots of clay and others (your home) have Rock Mountain gravel instead.  

Thomas, that sounds like an interesting history of the movement of soil etc.
BUT, Josiah, how is your name pronounced?
Buying in a truck load of clay may be better, it can be used in the garden as well.
You dont want an expansive or soluble clay for building.

John C Daley wrote:Thomas, that sounds like an interesting history of the movement of soil etc.
BUT, Josiah, how is your name pronounced?
Buying in a truck load of clay may be better, it can be used in the garden as well.
You dont want an expansive or soluble clay for building.

Hello, I missed this question for quite a few months. Figured its late but why not reply.

It is pronounced Joe-sigh-ah more or less.

Have you ever bought a truckload of clay? I am curious how much that would cost. The sacks of clay will work this time. But ultimately I hope to find some clay on my property for our next cob based project.