What is the ideal overall sand to clay ratio for combustion unit and bench mass.

I've been getting dirty refining some of my dirt from my backyard and in the rocket mass heater book it tells you to add so much sand to your clay to make your mortar for your combustion unit. And add so much for your bench but what if you feel your clay already has a lot of sand in it with some of the tests I have been doing I would say I am pretty close to 50 / 50 for sand to clay.

Should I make some test bricks and let them dry or stick them in my wood stove. I am unsure about getting this mixture right since the clay sand content would vary all over the world. I am also debating just buying potters clay just for my combustion unit to be sure this will hold together well and what ever if is left over if any will go around my pipe joints and such (areas that would be more prone to leaks). Thanks in advance.

John Towne : Consider looking at the permies forum ' Red pottery clay with sand for High Temp Mortar ' !
Even though some types of red clay mortar will 'fire' to be close to the function of the best of 'kiln bricks', there is enough variation between batches to make an answer to a general question silly if not worthless .
Fire up a batch and see for yourself, there is not only a difference in clay - Did you get a cone slump rating for your clay !- and then there is the difference in how 'crunchy ' your sand is ! Without meaning to you
asked a VERY open-ended question ! Be Safe ,Keep Warm, PYRO-Magic-ally Allen L.

This build is getting more complicated at every step. I am just wondering if there is a good ratio, a ballpark figure. I understand there will be a huge difference in clay throughout the land but I am looking for a sand to clay ratio to begin with. I could put a test brick in my wood stove and see how it turns out. The problem is that the process of removing the rocks, sand etc. from the clay is very time consuming, not to mention having to test each mix. If I had a ballpark ratio of sand to clay I could make that first and test that, then go from there. I guess I am just looking for a short cut since here we are in to the heating season. Also the ground soon will be too tough to dig. Maybe I misunderstood that these things can be built quickly, or I am looking to deeply into these things.

I would like to start my combustion unit asap, I have pretty much all the materials to make this part. The bench/mass can be built after combustion unit and pipes are all tested. I dont have the room to gather everything that will go into this. I will have to get the things as I need them. I am also having trouble finding perlite of vermiculite for my heat riser. The horticulture stuff is easy to find, but have read not to use this. I will just keep looking and researching, I really appreciate all the help being put forth as well.

Think insulation supply warehouse when sourcing perlite. I found mine at a roofing/insulation supply house after contacting the mfg of the stuff. I think commercially they pour it into cement block walls that need insulation. I don't know why they say the garden store stuff wont work, the mfg I called said it is the same stuff but more coarse and with water added. Perhaps let it dry out before making slip/perlite insulation and it could work just fine? You are wetting the stuff with the pancake batter clay slip anyway so i dont see what a bit of extra water would hurt.