noob questions: preparing clay, straw vital in cob?

Hello everyone.
I've been interested in many of the topics found here for quite some time.
Recently however I've been fortunate enough to buy an acreage and finally have room for some of my crazy ideas and ideas that people like you have already pioneered and proven effective. Like the RMH.

I do have a couple of questions to get me started.

1. How best do I prepare clay? There are a lot of people giving away free "clay" fill around here. It doesn't look like it'll make the nicest finished product tho.
I've heard that it should be screened first, then what? Do I just take the finest particles and mix them with some water? How do you screen it when it's wet and clumpy?

2. Do I lose effectivity if I leave out the straw in the cob? What's the purpose of it in the mass?

That's all for now I guess. Thank you all in advance.
I'm just glad to be here, every day is a gift.

Ashley Baptiste :Welcome to Permies.com, and a big welcome to the Prmies Rocket stoves/Mass Heaters Forum, With over 17,000 fellow members when you come here to talk
and learn there is a large number of members just like you, who started where you are now, and Want to talk about what you want to talk about, and they show up with widely,
some would say wildly different different view points and opinions !

Location, Location, location ! You need to share your location to your fellow members, The best reason for doing so is the strong possibility that you already have a near Neighbor
with Rocket Mass Heater R.M.H., or Cob Work experience !

Most of your Questions about Clay itself, could be shared with your fellow members in the Cob / Adobe Forums ! First you need to be able to take a sample of Your Clay in a clean
clear glass jar, mix it with water shake it up, and then note how it settles out, This will allow you to learn how much of your sample is clay, how much slit and How much is Sand.
this will allow you to figure out approximately how much builders sand you need to add to your clay to make test batches to further determine how to mix your cob to create -
Three different grades of Cob, Thermal Cob, Structural Cob, and Finish cob ! more on that later ! Google soil settlement shake test, and read up on materials needed, then go and
take several sample at each site, It is highly possible that you will find all the clay you need very close to your building site in belts or distinct layers with clean edges !

Good clay when you find it especially this season should be wet, and sticky you should be able to make a ball bigger than a golf ball up to baseball size, flatten it into a small patty,
squeeze it with out a lot of water running out of it, it should stick easily to your hand even when you turn your hand over, hanging there as you flex your wrist, then fingers !
Next, try to shape and roll it into a rod about as long and fat as a pencil, it should easily form this shape, and bend around your finger with out breaking, then back to the egg-
sized flat patty in your hand, repeatedly pat this patty with your fingers When the water is brought up to the surface your lump should be shiny !

With lots of practice this should be so natural, you can carry on a conversation with someone while testing several batches as you work at your building site !

Think of a fiberglass canoe, The clay and sand are like the resin and hardener, really really necessary, but you would not trust them alone to make a patch on your canoe,
the straw works just like the fiberglass providing the strength to hold the whole thing together, the three together make up the Structural Cob !

I strongly recommend that you go to cobcottage.com to get your PDF Copy $15.00 U.S.D. of Evans' and Jackson's Great book 'Rocket Mass Heaters', there is STILL no
other book in any language with more Rocket Stove / Rocket Mass Heater Family information ! ( and I don't make a dime ! )

While you are at cobcottage.com you should look at Evans book 'The Hand-Sculpted House' and as a companion book Michael Smith's 'The Cobbers Companion', you
can get these books here or through your lending library, or hopefully used copies from Amazon.com or my favorite Albris.com .

While you are waiting on the books you can gather the rest of your materials, and go to Permies.com sister site richsoil.com and click on Rocket stoves this will take you to a set
of Rocket Mass Heater Videos ether built by professionals or from directions from Pro.s This is much better stuff than most of the Jreck in U-tube land ! This will keep you busy a
while !

For the Good of the Craft, Think like fire, Flow like a Gas, Don't be the Marshmallow ! As always comments and questions are solicited and Welcome BIG AL

Ashley Baptiste : This is SO very timely I had to share it ! Please go to the Homestead Forum and Checkout my reply to Jason Millard's Thread/post ''120 acres in the
North Country -''

Here is a gentleman who has a 5 year plan to get moved onto recently purchased land, one Post and he is connected with some one who can help him long distance ! In this
case he got me, a near neighbor with experience. Under the heading of nothing ventured, nothing gained he gained ! Here the odds while a little long, worked in his favor Y.M.M.V.

For The Craft ! BIG AL

wow thank you very much al.

there is a lot of good info there for me and I appreciate it.

so the straw are the fibres in my carbon fibre so to say. ok cool, over time its going to decay though isnt it? as for the clay the stickier it is the more sand I can get away with adding I take it? this builders sand is that something special?


I'll have many many more questions as I go. like this one. I picked up a ton of free cinder blocks today could i lay them down on their sides and say two rows and pump my exhaust through there? they would be both "duct" and mass. I would build a header at either end and cover the whole thing with cob to seal it in. thought?

Ashley Baptiste : O. K., Kinda in order, yes its your fiber,Thermal Cob next to the base of your R.M.H. and your horizontal ductwork, needs intimate contact to seal all the nooks,
cracks, cavities, crevasses, etc. to seal up your duct work, it is also there to make contact so that the heat from the hot exhaust gasses can radiate up though the Cob and here
you do not want straw as it would be insulating.

We don't have to worry about rotting straw - mostly ! If the very best wood we can burn is super dry wood cut and stored last year with a 10% Water Vapor, then thats our
benchmark !

Your (future R.M.H.) works best with wood that dry, however we want to talk about the 60% of the wood that we can get to pyrolyze or release its volatile gases, this is the part
of our burn that gives the super high temperatures, and great efficiencies to our stove, properly consumed in our R.M.H. we end up producing exhaust gases consisting of just
Carbon Dioxide, and water vapor. This is about 60% by weight of the fuel value (= HEAT!) of the wood, leaving - just charcoal !

If we have done our job right up to here the cob will suck up some of the water vapor and some of it will travel through the Thermal Mass, however the Cob itself will rarely see
more than 15% total water vapor 'locked', in the Cob this is practically Death Valley Desert ! Part of the reason for this happening is the tail end of the burn, when the R.M.H.
is at Maximum temperature, (and Its Internal 'Dragon' is happily Bathing in the Heat ) this is when we burn up the charcoal 'mostly' This is the driest part of the burn and will
'pull back' some of the water vapor out of the Thermal Cob, This is a Gross over simplification, but pretty accurate ! Think Desiccated Mummies !

Yes, more sand is better, Clay hides a sinister side, depending what type it is, it Swells when wet and shrinks as it dries , We use Oregon Cob, which means a LOT of sand to 'lock'
up the Clay and restrict its ability to swell! Think two big R.C.M.P.s frog marching off the clay, keeping it from mischief !

For using sand in building we have to consider three (3) types, 1) Sand from the beach, polished smooth, round with no sharp corners = Bad, 2) 'River Bank sand, with corners but
not 'sharp' > usable but :p , and 3) Builders or Sharp sand, lots of sharp corners, a small lump of cob made with builders sand when held up next to your ear and worked will sound
gritty= Best !

Cinder Blocks are Crap, and there is/are lots of reasons why they are cheap, here they don't handle heat well, and they are too porous, we can seal them with a combination of Clay
Slip / Flour Paste, but we will be only solving some of the problems. You can use your cinder blocks to isolate the high temps radiating off of the Bottom of your R.M.H. stoping heat
energy from radiating away through your floor (Can be Good, can be Bad !), if you are stuck using an existing building this will allow you to use a R.M.H. sitting on a wood floor !
Remember that you are adding as much weight as a waterbed ! Additional Bracing may be in order !

Always remember and never forget Cob will not 'burn down', it will not 'rot', bugs won't eat it, and its dirt cheap ! Repeat that to yourself Daily !

If someone wants to deliver you building supplies, AND you have room, and they are willing to use their fuel to get it there, thank them fully (beer works) and use it when you can !

For The Good of The Craft! As always, comments, and questions are solicited and Welcome ! Think like Fire, flow like a Gas, Don't be the Marshmallow , PYRO-Logically Big AL !