Smoker Body: Cast Concrete Cylinder?

[slack]

Found this forum when googling possible problems of cooking in concrete.

Being a noob here, this may be heresy, but back in 2010 I built an electric, closed loop control, web enabled, text messaging meat smoker using two terra cotta flow pots, You can see the build here....

Since then I have nuked the touchscreen, and dedicated temperature controller, and replaced with a single PLC (Siemens S7-1200). Which fires a 25amp solid state relay as the PWM (pulse width modulated) output of the PID controller. The PLC also serves up custom web pages that allow for setting and monitoring grill and payload temperature, but I haven't gotten too fancy with the graphics just yet, nor have I completed the SMS texting bit on the new platform. The PLC approach reduces cost somewhat.

So why cast concrete?

1) The original build I gave to my sister as a combo house warming / birthday present this year, and I am having NO luck replacing the terra cotta. So driving home after another bust at a local garden center I thought I'd just make my own grill body. And concrete seemed the best choice for a layman.

2) Making the mold could be problematic, but I would have control of diameter and height. (I can think of one high tech solution to this problem - a 3D printer).

So my question for you pros is - would you have a recommended diameter to accomodate a 'standard' round grate that is available on the market today, and will be for the near term?

 

[slack]

Found this forum when googling possible problems of cooking in concrete.

Being a noob here, this may be heresy, but back in 2010 I built an electric, closed loop control, web enabled, text messaging meat smoker using two terra cotta flow pots, You can see the build here....

Since then I have nuked the touchscreen, and dedicated temperature controller, and replaced with a single PLC (Siemens S7-1200). Which fires a 25amp solid state relay as the PWM (pulse width modulated) output of the PID controller. The PLC also serves up custom web pages that allow for setting and monitoring grill and payload temperature, but I haven't gotten too fancy with the graphics just yet, nor have I completed the SMS texting bit on the new platform. The PLC approach reduces cost somewhat.

So why cast concrete?

1) The original build I gave to my sister as a combo house warming / birthday present this year, and I am having NO luck replacing the terra cotta. So driving home after another bust at a local garden center I thought I'd just make my own grill body. And concrete seemed the best choice for a layman.

2) Making the mold could be problematic, but I would have control of diameter and height. (I can think of one high tech solution to this problem - a 3D printer).

So my question for you pros is - would you have a recommended diameter to accomodate a 'standard' round grate that is available on the market today, and will be for the near term?

 

[timetosmoke]

That is amazing setup. Looking forward to you next model!

 

[michael ark]

Concreat is heavy. Have you looked at pottery material ? I rember in pottery class our professor made a outdoor kiln that was wood fired that was super lite and real easy to work with. I'll see if I can find out what it was.

 

[ironhorse07]

My other concern with cast concrete besides weight would be depending on what wall thickness yoy would need it could take forever to heat up. Would be really stable when it got there though.

 

[daveomak]

Slack, morning.....  So if I understand you correctly, you want to build a smoke chamber out of concrete....  Concrete has a thermal mass that takes a long time to heat up....  Since you are pouring it yourself, consider making a crete of "hypertufa"...

http://en.wikipedia.org/wiki/Hypertufa

It would be lighter in weight and have advantages to not freeze cracking.....  You could adjust the materials to be "food friendly"....

I have made planters using this method.... never a BBQ though....  They need to have thick walls, due to the porosity, so they won't break...  Fiberglass strands would be a good reinforcing webbing as it won't melt and is pretty inert...  You could use different sized garbage cans for a two-sided mold etc...  and they would act as the required humidity control chamber for the long curing process....

Just thinking out loud...

...  That would be an interesting project....  Keep is in the loop on your venture.....   Dave

 

[slack]

Concreat is heavy. Have you looked at pottery material ? I rember in pottery class our professor made a outdoor kiln that was wood fired that was super lite and real easy to work with. I'll see if I can find out what it was.

I was hoping to avoid the whole Kiln thing. But hey if I could do it in clay - Carolina red clay that would have a nice tie in.

 

[slack]

Originally Posted by Ironhorse07  

My other concern with cast concrete besides weight would be depending on what wall thickness yoy would need it could take forever to heat up. Would be really stable when it got there though.

I always thought the appeal of the big green egg and it's ilk, was the thermal mass vs. metal bullet type smokers.

In any case I will have to consult with the mechanical engineers at work regarding wall thickness. And it occurs to me glass beads or some other inert light material could be added to the concrete or mortar mix to make the end results lighter. Again, I will talk with the mechanical guys about that.

 

[slack]

Hey forum mods, sorry for the double thread. Any chance you could merge them?

 

[slack]

Slack, morning.....  So if I understand you correctly, you want to build a smoke chamber out of concrete....  Concrete has a thermal mass that takes a long time to heat up....  Since you are pouring it yourself, consider making a crete of "hypertufa"...

http://en.wikipedia.org/wiki/Hypertufa

It would be lighter in weight and have advantages to not freeze cracking.....  You could adjust the materials to be "food friendly"....

I have made planters using this method.... never a BBQ though....  They need to have thick walls, due to the porosity, so they won't break...  Fiberglass strands would be a good reinforcing webbing as it won't melt and is pretty inert...  You could use different sized garbage cans for a two-sided mold etc...  and they would act as the required humidity control chamber for the long curing process....

Just thinking out loud...

...  That would be an interesting project....  Keep is in the loop on your venture.....   Dave

Thanks for the link. Will definitely have to consider that, or something similar - tweaked for the application.

For the mold I am thinking about a reusable mold built from 3D printed pieces of ABS that could interlock together (or simply be mechanically bound together at cast time). We have a 3D printer at work, and if I supply the material they may allow me to print freely. Failing that, plenty of online rapid prototype places will do it. The trick will be knowing the maximum working size of the printer, and designing the pieces to fit within that. I'm not a 3D modeler, but for good 'que I am willing to geek out and learn it.

Hey since you are a mod - could you merge this thread it's twin I accidentally created?

 

[ponderingturtle]

I would wonder about dehydrating the concrete and thus weakening it. You can certainly weaken concrete by baking it in an oven, so it could be an issue here.

These concerns might not be warranted in this application but it is making me steer clear of it when I am designing a simpler PID controlled unit.  I wish I knew enough about PLC programing to do this, but I have yet to get to learn that at work.