Cinder Block (CMU) Offset Smoker





Introduction: Cinder Block (CMU) Offset Smoker

For a small fraction the price of a heavy steel smoker, you can setup a large capacity cinder block version. Not only will it be cheaper it will be better insulated. Follow the instructions attached for a very effective, efficient and not bad looking unit.

Step 1: Design & Dimension

Review design dimensions.

Step 2: Clear Area

  1. Clear appropriate sized area with offsets as needed.
  2. Soften and level dirt or ad layer of sand.

Step 3: Procure Cinder Blocks & Bricks

  • Cinder Block: 8x8x16 (Qty. 60)
  • Cinder Block (1/2): 8x8x8 (Qty. 15)
  • Cinder Block (Caps): 8x2x16 (Qty. 16)
  • Clay Brick: 4.5x9x1.75 (Qty. 24)

Step 4: Base Layers

  1. Place base layer of cinder blocks and use level to confirm flatness.
  2. Alternate seem on each level.
  3. Eliminate all air gaps.

Step 5: Complete Firebox

  1. Build firebox with rotated CMU bricks for air inlet and outlet as shown.

Step 6: Complete Chimney Structure

  1. With a chisel, break a 1/2 brick into half again so that the chimney has an opening as shown in picture.
  2. Stack chimney to 3 blocks high for appropriate air draw.

Step 7: Add Top Caps

  1. Place top caps on alternating seems from cinder blocks underneath. (Top caps will ad a flat surface for lids to seal better)

Step 8: Lid Construction

Lid Dimensions: 30.5" x 38" (Qty. 2)

  1. Cut plywood to dimensions.
  2. Procure Heat Shield Insulation (4 ft x 6 ft) and cut to same dimension as plywood.
  3. Using a staple gun, apply insulation to bottom side of wood.
  4. Fasten two lid pieces with hinges in middle and and handles.

Step 9: Add Clay Bricks

  1. Line the inner firebox with clay bricks for extra heat protection for the concrete blocks.

Step 10: Rebar Grate Support

  1. Measure off alignment for rebar supports. (3 places)
  2. Using a 1/2 inch concrete drill bit, drill holes through only one side of blocks.
  3. Insert 25" long, 3/8" rebar.
  4. Procure or cut, 3/4" X 13 ga. flattened expanded metal sheet to 22" x 53"
  5. Place expanded metal on top of rebar for a cook grate.

Step 11: Fire Box Lid

  1. Procure 29" x 31", 3/16" thick carbon steel plate.
  2. Drill and bolt in handles for easier removal (not shown)

3/16 steel plate is necessary for firebox as temperature here will be too extreme for thinner materials

Step 12: How to Use

Now you're ready to test it out!

  • Use a left over block as a damper for your incoming fire vent. Slide back and forth to adjust heat.
  • Leave stack vent open at all times.
  • Add another expanded metal grate over the fire-pit if you would like the option to grill over the fire. (Good for tri-tip and chicken)

(This specific pit has about a 20 degree difference from one side to the other....which is actually very impressive.)

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26 Discussions

I might have missed it... But what is the overall cost of this? Considering how much of a surface area this gives and how much room it takes up... If the cost is low this could be something everyone should do.

3 replies

Craigslist is an excellent resource for cheap cinder blocks. Some people give them away for free even.

hahahah I didnt even think of that. hahahah Great build

It can definitely be done for cheaper if you have better resources and do a little more shopping around. But it cost me right around $330 total. The blocks themselves cost about $125. Having the expanded metal and steel plate lid cut to size were a large part of the expenses as well.

F.Y.I. ... you need to "season" any exposed cinderblocks; i.e. do several pre-burns to coat and seal their surfaces, BECAUSE the cinderblock material is toxic, and you don't want THAT on your meat. Just sayin' ...

Question: Are you burning the wood directly on the ground in the firebox?

Would there be any benefit to raising the fire up using a heavy grate or a rebar mesh in order to allow the ash to fall below?

Also, how do you dispose of the ash accumulation? Through the vent hole seems labor intensive in addition to digging out your sand with it?

1 reply

I'm burning wood directly on the ground. I start with a bed of hot charcoal and ad the splits on top. I've found no need for grates as the fire burns nice and even.

I just use a an ash shovel to scoop out from the top (with the lid firebox lid removed). Takes about 5 minutes if that. It's hard packed dirt underneath. No problems at all.

A great tutorial! I'm going to drill a couple more heights for rebar holes so I can try that "whole pig" thing.

Now you just have to add a pizza oven on the end with a additional fire box and you have it all. :-)

Good day, very cool. My son and I are making plans to do this while my wife is on vacation with her sisters. No need to explain why this is the preferred time is there!

1 reply

Have fun and post pics on here when you're done!

Like Chef John, I'm interested in how you eliminated all air gaps. Did I miss something in the tutorial? It doesn't look like you used mortar... did you use a sealer, or other material to secure, and minimize air gaps?

2 replies

I suppose I should have worded it a little better. "Mitigate all air gaps." Without mortar you won't be able to "eliminate" them. With this design I have had almost zero smoke leaking through.

As with most natural fluids, smoke should take the path of least resistance. The bricks are much tighter than the path of flow you created with the open bricks. As long as they remain unobstructed, the air should "choose" to flow through that pathway. Get a few cookouts and grease popping and you'll probably generate some sort of "meat mortar" that even further seals the edges.

Really good idea as I have been thinking about building a smoker as we do not get the variety of choices here as in N. America where I first used one. I'm not convinced about using wood for the lids though, perhaps a thin steel sheet would be better.

1 reply

Same problem in California. A good steel offset trailer is twice the price here vs. the south. Steel sheet would work great for the lids. It's just more expensive and doesn't provide the same amount of insulation. Would definitely be more durable though. So far the wood lids have worked great. With the insulated lining, they don't take a lot of heat. I will be covering/protecting them during the rainy seasons of course.

IN the procedure you said Step 4

  1. Place base layer of cinder blocks and use level to confirm flatness.
  2. Alternate seem on each level.
  3. Eliminate all air gaps\

But you didn't say how .. was it just to lay the cinder block as snugly as you could on top of each other or ....

1 reply

Correct. Cinder blocks are a little irregular, so shuffling certain ones around and even filing off irregularities can help. Getting your base layer tight and flat is the most important. But this design has no mortar, so just pushing them snug is all that is required.

Wouldn't a piece of Concrete board be better than plywood? Like you would use in a bathroom floor.

1 reply

I've still got the same board on mine after two long pig roasts and several smaller uses between two summers, so you just have to keep the top out of the weather.