Denny Romero

Glenn Herbert wrote:It appears that you don't have a secondary air supply. This is some added complexity, but may make a real difference in completeness of combustion. The best current practice involves a channel recessed in the firebox floor (so the air gets preheated) and a metal tube rising just in front of the port to inject the air where there is maximum turbulence. Look up "pre-port injector" for configuration and sizing.

Hey Glenn thanks for the reply. I do have a secondary air it's under the barrel lid. It's about 1 1/2" squared. I know it's working because if I drop dust or something in front of the barrel it sucks it in. I haven't had the chance to clean it all and try it with hard wood yet. But I will soon.

Here are some photos. The heater is burning amazing. Still no where near done. I'm going to add more section of pipe to make my bench an L shape with a bell at the end.

Mixing clay with anything is really tough work lol. Love decided that I'm going to lay a brick wall all around the bench and fill around  the batch box with clay sand the rest of the way and I'm going to put gravel in the bench. The upper two inches I'll mix clay and sand to seal it. Then on top some slat mortored in.

My question is I'm getting a lot of black dust. Has no smell and it's  dust, wipes right off. Could that be from burning these 4x4 lumber?

Last picture is how I get my draft going works amazing the paper and all that was driving me crazy. I heat for a min in the riser then pit small 4x4 in the back and light them up for about 30sec.

Well on a better note. Here's my progress.

My first layer give or take 2 1/2" thicker in the back, was potter's clay mixed with a lot of perlite 10 bags 8qt each. I couldn't find the big bags well I could but, wanted to get this part done this week and not wait for shipping.
Btw there was no mesh in it so it kept cracking as it dried and I kept filling gaps with more.

Next layer is clay and course sand about another two inches. I did put chicken wire in that layer. Let's see how much it cracks. It's taking a very long time to dry being in this cold basement. I have a fan right on it. The rest will be clay sand straw mix. Can I use hay?

That is the door I'm going to use on it. I may torch some more holes in it just gotta see how much air that one pulls. Gonna build that next because I'm going to bolt it down to the concrete slab.

Hope I'm doing an ok job.

Bruce Woodford wrote:You can build a steel core as you originally planned BUT rather than insulating it, you MUST air-cool it! Whenever steel gets over 900F it will glow red hot and corrode very quickly! RMH temps far exceed this but air-cooling on the exterior will enable you to avoid overheating your steel core. See my 7" steel air -cooled RMH at  https://permies.com/t/69632/Building-tube-steel-air-cooled for more details on safely constructing a steel cored RMH that will last.

I decided to go with a batch box style. I'm still working on it.

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?

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.

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.

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.

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?

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.