Converted my J tube to a batch box

Much better results with the batch box. Still have a lot of work to do but here is some pictures.

My clay/ insulation brick is peeling away as it dries. Does anyone have a tip to stop this?

I have pottery clay. Tons of it the pottery guys around here gave me.

Denny, are you mixing sand into your clay ?  Pure clay like a potter uses would need 3 times the amount of builders sand mixed into it.  Without sand your clay is not cob.  It will crack without it.

thomas rubino wrote:Denny, are you mixing sand into your clay ?  Pure clay like a potter uses would need 3 times the amount of builders sand mixed into it.  Without sand your clay is not cob.  It will crack without it.

Ahhh I didn't know that. I'm new to this. I thought the sand was just to add more mass to the clay. So I guess ill let this all dry and peel off and get some sand to mix with it. Will the sand keep it from peeling back?

It should bond better. The sand thermally stabilizes the cob, keeps it from moving as it dry's/ heats.   Have you acquired the builders guide yet? It explains all this.

thomas rubino wrote:It should bond better. The sand thermally stabilizes the cob, keeps it from moving as it dry's/ heats.   Have you acquired the builders guide yet? It explains all this.

Ok. No I haven't. Is there a link where I can buy it. I will buy it today.

I'm really liking this batch style heater.

Not really a link but go to amazon and paste in this. ( The Rocket Mass Heater Builder's Guide: Complete Step-by-Step Construction, Maintenance and Troubleshooting  )    

thomas rubino wrote:Not really a link but go to amazon and paste in this. ( The Rocket Mass Heater Builder's Guide: Complete Step-by-Step Construction, Maintenance and Troubleshooting  )    

Ok thank you.

I would scrape that clay off before it dries anymore and submerge it in water and reuse it with  perlite mixed in like you were casting a riser--The Perlite makes it slightly less robust, but it is a better insulator. Then use the sand clay mix for the surface. I like to use a paintbrush and water to smooth the final surface, and if minor cracks appear just use a very loose clay to fill in the cracks--

btw, cob also has straw mixed in, but I generally don't bother with straw in my stoves --makes it easier to take them apart and rework the clay with water  when I remodel, and as fast as the designs are evolving, that is quite frequently.

As a potter, I can attest that clay that is bone dry will wet and break down much faster than clay that is nearly dry (not changed color yet).

As long as you don't need the cob to hold together on its own, eliminating straw would be fine. If you want to make a larger structure like a bench, straw in the outer few inches at least will make it much more crack-resistant. Clay plus perlite (as much perlite as the clay will hold without being crumbly) will be a fine insulator, and a layer of clay-sand-straw cob will give a strong tough surface. For thermal mass areas where you want to absorb heat and not prevent its movement, lots of sand in the mix is best, to add mass and reduce shrinkage.

bob day wrote:I would scrape that clay off before it dries anymore and submerge it in water and reuse it with  perlite mixed in like you were casting a riser--The Perlite makes it slightly less robust, but it is a better insulator. Then use the sand clay mix for the surface. I like to use a paintbrush and water to smooth the final surface, and if minor cracks appear just use a very loose clay to fill in the cracks--

btw, cob also has straw mixed in, but I generally don't bother with straw in my stoves --makes it easier to take them apart and rework the clay with water  when I remodel, and as fast as the designs are evolving, that is quite frequently.

There will be no scraping lol. It's peeling off. I broke a piece off and thru it in water and it broke down. So I'm going to let it dry out and then re wet it. I can't wait to finally have it done.

Glenn Herbert wrote:As a potter, I can attest that clay that is bone dry will wet and break down much faster than clay that is nearly dry (not changed color yet).

As long as you don't need the cob to hold together on its own, eliminating straw would be fine. If you want to make a larger structure like a bench, straw in the outer few inches at least will make it much more crack-resistant. Clay plus perlite (as much perlite as the clay will hold without being crumbly) will be a fine insulator, and a layer of clay-sand-straw cob will give a strong tough surface. For thermal mass areas where you want to absorb heat and not prevent its movement, lots of sand in the mix is best, to add mass and reduce shrinkage.

Thank you for the help on the mixing of clay to make cob. Yeah I'm gonna let this clay dry out and put it on a wire mesh under water to separate the rock from it. Trying to mix rock into it will put a number on your hands.

By the way. I got my clay from potter's. It is their scrap they have laying around wet in buckets. The clay on top is pretty smooth and mushy. Well after that it gets really hard to work with. Is the mushy stuff good to work with or should it be mixed somehow with the more dense stuff?

If there is a smooth mushy layer n top, it is probably lacking the coarse grog (grit) which makes clay more shrink-resistant. It will be better to mix it up; adding sand is also beneficial.