Clean clay a problem?

So I'm looking at making a rocket stove with an attached cob bench. I've never worked with cob but have been researching it extensively. I've recently begun gathering materials and received an excellent tip on a source for clay and the one thing that I noticed right away is that the clay is very clean, next to no silt or anything besides clay. And in my reading I've noticed people reference "clay rich soil" which I'm curious about.

Does it matter if I use pure clay (without "soil") in my cob mixture or should I be grabbing some dirt from my back yard to mix in as well?

Quinn Mas-aboudara : A slightly late Welcome to Permies, as you will be building a Rocket Mass Heater R.M.H.,and Thermal Bench, you may want to post further questions as
a new posting in the Rocket Stoves Forum Threads !

A little silt in with your clay is not a problem, The size, and grittiness of the Sand that you mix with it is much more important ! Clay swells when it is wet, the sand retards the
amount of swelling, and also the shrinkage in drying ! Clay also expands when heated,and shrinks with cooling, every batch of clay has it own swelling and shrinkage rates !
The sand retards both the swelling and the shrinkage preventing , or a lest reducing any cracks from to rapid drying !

If you had bought your clay in powdered form in bags, the best would be Fire clay. It is the best not because it withstands heat the best but because by not expanding/shrinking
as 'much', it is not as likely to crack as compared to other clay out there ! Reducing friability and failure makes It 'good fire clay' again gritty 'builders sand' buffers the shrink
-ing and expanding of all clays ! If this interests you you can do a search for grog for additional reduction of swelling,shrinkage with high heats !

Please consider going to rocket stoves.com to get your PDF copy $15.oo U.S. of Evans' and Jackson's great book - ' Rocket Mass Heaters ' - there is no greater source of
'Rocket Stove Family information' in one book in any Language ! ( there are adaptations out there in French and Spanish for those who comprehend better in these languages )
-And I don't make a dime ! This will help you with your understanding of the R.M.H.s, and the vocabulary of your fellow Permies Rocket Stove members !

For our Craft and the Future ! Be safe, keep warm ! PYRO Logically Big AL ! - As always, your questions and comments are solicited and Welcome ! A. L.

Thanks for the reply! I've been experimenting and messing with the clay/sand mixtures (my wife would like a cob "gazebo" in our back yard) now that I'm getting the mixture down.

I had actually simply found a clay bank that was super clean. I dug off the top foot or two of clay and collected clay from under that. It was amazingly clean! I did a water test and it showed a very low amount of sand and silt and primarily clay. The clay is super clean with barely anything in it! I'm currently drying half of it to powder it for easier mixing and have been experimenting with the other half making cob bricks.

So far I've found that it gets super thin and "soupy" then I start adding sand and it starts to firm up a bit but it doesn't look like anything I've seen in videos on making cob or in the various books/manuals I've found so I've been experimenting with various soils.

So far wood ash seems to be excellent to get that consistency and in the test bricks I've made it seems to hold together real well.

I've also been experimenting with different "rebar" material such as straw, cedar bark, and combinations and so far I've been super impressed with the cedar bark even more so than the straw.

I just finished several different bricks and I've tested them by dropping them from approximately 12' onto solid concrete. And so far the jury has come back with the verdict that the cedar bark bricks are amazing! One of the test bricks I dropped three times from my test height before it developed any major cracks! That's exciting since I figure that I won't be dropping my bench so it should have some amazing strength and resiliency!

Another thing that I discovered was that I had wondered why everyone used their feet to mix the cob. Now after mixing about 50lb of test batches by hand I've stumbled upon the true secret... It saves my back by doing it by foot!

Quinn Mas-Aboudara : Fantastic, There are a couple of people I would like to share that news with and will do so - but tell me how do you prepare the cedar bark !

As an avid woodsman, I prefer a simple wood fire at night a short distance away from my tent. For that reason I have always carried a small cheap lighter and a
candle. Recently I have added two pieces of cedar bark, both about the size of Playing cards! Both pieces are made from longer strips of bark that I place down
on the gravel of my drive way. Running over them repeatedly softens them, and partially breaks them down ! One of the pieces I 'char' like char cloth !

Always having a lighter whose spark will still work even if it runs out of fuel, and the two different stripes of prepared before-hand Cedar bark (and a candle) means
I will always have the ability to have a fire !

I mention this because Im thinking about Cedar bark prepared by crushing/shredding under the wheels of my car ! Please post back and tell me how you prepare
your Cedar Bark !

For the Future/Good of the Craft ! Be safe, keep warm ! As always, comments / questions are solicited and welcome ! PYRO-LOGICALLY Big AL !

Late note ! Wikipedia says there are 13 different types of Cedar wood. Im using Eastern (american) Red Cedar, very common for Fence posts because of its rot
resistance, the bark is usually peeled off and discarded, the Red Cedar posts dry better that way, and handling is easier ! Where are you and do you know what kind
of cedar you have !

I'm in southeast Alaska and I'm using pacific red cedar (Thuja plicata) bark. I typically harvest it in mid spring and let it dry then once dry I simply sit back in my reclined and peel it strip by strip from the top to bottom. I've tried breaking it up several different ways and have found it much less effective than just doing it by hand.

Quinn Mas-Aboudara : I am familiar with peeling the bark off of our Eastern Red Cedar and White Cedar, Rob Roy, 'D.I.Y. Home Builder, and Author', Is Famous for
being at the front when Cordwood house construction had a re-birth down here in the lower 48. In fact he lives about an hour away ! With several books out there and
blogging on his own, and sometimes here at Permies, it would be very easy for me to have missed any mention of using Cedar bark in Cordwood housing - he is a
member Here !

As we were talking about using the Cedar bark as Fiber to make stronger Cob, I was interested the whole process, Of PreTreating/Treating, cutting to size, mixing, and
Ratios and Amounts used ! - I do understand that this is a work in progress! AND, It is Your work in progress and takes up all the time you can give it ! Anything
you want to share, and can find the time to do so, will be useful and appreciated!

I have never heard of using Cedar Bark in this way Before, and I am Very pleasantly surprised to find that the bark could be used that way. I would have thought that the
Cedar Oils would have made a problem in 'Setting-up' the cob,( ?like concrete? ) and also increased the likely-hood of Fiber loss do to Charing !

I re-read your Earlier posts, and find myself even more impressed with your results! I wanted to ask Several People if they had any knowledge of anyone having similar
results, It would be very nice to turn a waste product that composts poorly into a Large Plus as a reinforcement/strengthening material !

If you want to, and have the time to answer these questions, I think this topic should be shared here in the Cobs Forum with links in Rocket Mass Heaters R.M.H.s ! I
would think that a New forum topic/thread like '' You've Got Cedar Bark In My Cob '' should create a lot of visits to your Topic, and hopefully generate the Creation and
Dissemination of more Knowledge in building with Cedar bark in Cob ! I promise to do a careful google search for information here, and am looking forward to reading your
next post(s)!

Thanks again for sharing your discovery, seemingly small things like this - have Snowballed into Avalanches of new information, widely shared by the 17,000+ members
here at Permies.

For the Good of the Craft ! Be safe, keep Warm ! As always your Comments and questions are solicited and are Welcome !

Quinn Mas-Aboudara : -And there it was, In the Cob Forum, right under my nose! A forum/thread - ' Eastern White cedar Bark ' - the entry by Jay C. White-Cloud is
interesting, and I expect very accurate as an over view of the whole process of working with the Bark of Eastern White Cedar ! I have played with the inner bark and
can report that preparing the inner bark is a lot of work ! Somehow I assumed that you were using the outer bark only. My mistake,what part(s) are you using ?

I realize that I did not even think to address the issue of the two layers, so now we play a little catch-up ! I believe that irregardless of the amount of work involved,
using the cedar bark in a Rocket Mass Heater R.M.H. is very do-able and will certainly quickly show you if you want to proceed with your Outdoor project !

I had thought to P.M. Him, and invite him into the conversation, what do you think ! Again, I think there is much potential good in this line of research, and if there is
something that can be learned here I want to be part of it !

For the Future Good of the Crafts ! Be safe keep warm ! As always, your comments and questions are solicited and WELCOME ! Big AL !

Ok so apparently it's been a while since I've been on here and to be honest I haven't had a whole lot of time to spend experimenting with everything, however I did manage to do one thing this summer that may help out with some of my future endeavors.

Last summer I built a smoke house, nothing fancy, just four walls, a small door, hanging racks, etc. Now when I built the smoke house I built it in the way that has been passed down in my family with a small open fire pit on a bed of sand and gravel in the center of the smoke house which we then build a small, green alder fire and maintain at a decent smoulder.

This summer I felt that this may be able to be improved upon and I also wanted to try experimenting with the idea of a smokehouse/drying area since my wife doesn't particularly enjoy the smell of fish or venison drying in the house and absolutely adhors the image of strips of meat hanging from the ceiling above our bed.

SO! That said I built a horseshoe shaped fire ring in the smoke house using cedar based cob and a clay wash. I allowed it to dry and firm for about a week and then fired the entire thing in the smoke house using green alder (which reaches temperatures high enough to forge metals with and was utilized in pioneer days in lieu of coal which was sometimes difficult to obtain in Alaska).

And it turned out beautifully! Granted because of the open design of the smoke house the structure did not retain the heat required to dry meats, so we still had meat hanging over our bed for the summer, but the cob fire ring worked nicely and I was able to get some insight into charring recently after a horrible windstorm blew over the smoke house.

The short of it is that I ran out and grabbed the fire ring which was being exposed to some very nasty weather (the clay wash was holding up very nicely however) and because I realized that I would be having to rebuild anyways I simply broke open the fire ring. Besides the fact that this was actually a bit more difficult than I had initially anticipated and required the use of a hammer I was also anticipating that the cedar would be heavily charred as had been mentioned previously. To my surprise I could not find evidence of charring in the cedar bark! And this is with direct heat to the cob itself (granted there is a thin clay wash but not enough I would think to dissipate the heat?)!

I would like to note also that the fire ring/smoke house was heavily utilized this summer, averaging about 35-40 hours a week between myself, my brother, and other friends and family, it was used pretty much the entire months of July and August... much to the horror of some of my more "civilized" neighbors...

Needless to say I am impressed and amazed and am looking forward to some favorable weather so I can begin working on the RMH project again.