Offset Concrete Block Hog Smoker

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Original poster
Jan 23, 2012
Brooklyn, NY
So I started this project a while ago for a big BBQ that I have each year.  I always want to do something new and decided that this was the year of the hog.  I originally began with an idea for a reverse flow concrete block smoker, but after realizing how much steel was going to cost me, I altered my plan a bit. 

I really wanted to cook a hog the way I've seen it in a lot of other posts: in a big concrete block pit, but I also wanted ease of access to the fire and increased temperature stability.  After continually changing this design over and over again, this is what I've come up with.  I also had to adjust as I was trying to do this on the cheap.  Most of the materials that you will see me use are recycled, dontated or found on the side of the road.  If you plan ahead with these things and exploit some online resources, it's amazing what you can get for free. 

I will be doing the hog on Memorial Day weekend, but after I get the last piece of steel I need for the firebox from a buddy of mine, I will post some pics with whole chickens as a trial run. 

Found a decent spot and removed what little grass there was.  Then leveled the ground as much as possible.


Leveled each block in all directions.....


...and between sides to ensure overall level of the entire structure.


On the firebox end, I cut a block in half using a masonry cutting disc (about $3) in the circular store.  You can get these at any home improvement shop.  Just make sure it's the right size for your saw.  You may ask me why I just didn't add a block on the end turned sideways, but the dimensions needed to align with the plans that I had for the top.  It'll make sense when you see it below. 


Block turned sideways to allow the heat and smoke in. 


I began the second level with the joints of the first in the midle of each block (typical block construction).  I have seen some folks just stack on on top of the other, but it lends itself to some instability. 


I also lines the bottom with some brick (mostly to keep the weeds down).  I like it and think it gives the pit a nice finished feel to it. 


....more to come.  I am finishing this thing up today.  I have a bunch of other pics from other components, but I want this post to make sense in case anyone wants to build one like this. 
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OK  I  am in ! Not quite sure I  have a handle on it yet.You dont mortar the blocks just stack them? 

I will wait until you post some more pics of firebox bit rather than ask a bunch of other questions.

Like the idea of reclaimed & recycled.
Yup, just stacking them for this project.  You will still retain plenty of heat and the little amount of air that may get in is good for the cooking process anyhow.  THink of it like extra little vents.  Once I have the whole post up, I will go through all of the possible upgrades that you can do to this depending on whether you want to make it a permanent structure or not.  I don't own the property, so I have to consider the need to move it in the future.  It is plenty stable (I was walking on the walls yesterday). 

If you want to replicate the design, you could definitely mortar the bricks.  I would also go ahead and increase the insulation by filling them with perlite.  You will basically have a completely heat proof structure then and winds will not effect you at all.  You can find perlite in most garden shops, but you are beter off getting a large bag of it in a masonry supply store.  In the US, they also sell perlite inserts and concrete block with perlite alreay installed for firewalls.  Perlite is the little styrofoam looking white things that often come in garden soil.  Everyone thinks that it is styrofoam, but it is actually volcanic silica rock, superheated to over 2000 degrees until it pops like popcorn, giving it the light fluffy feel.  It is completely inert and can never burn (unless you put it in front of a jet engine). 

I will go more in depth into what you could do with this in the future posts.  THanks for the comment. 
Ok, well here is where I got yesterday:

There are four actions that I completed in this picture: 

First I finished the second layer of concrete blocks going around.  Extremely easy to do once I had the base done and nice and level. 

Second, I wanted to get a little steam into the system, so I put a big steel roaster pan a few inches from the heat source.  I am toying with a design to have a water pan suspended in front of the heat source, but will have to wait until I can get my brother to weld a few things for me.  In the meantime, I can just add water through the cooking grate to the pan.  I feel that increasing the ambent humidity in the cooker is vital.  First off, for long cooking times (like everything we do) it allows more moisture to stay in the meat.  Completely dry heat can quickly dry out any piece of meat.  Also, it will help regulate the temperature.  Stability in air temperatures is completely based on the amount of humidity in the air.  The water is what holds the heat.  This is exactly why you will hear of people freezing to death in the desert (think Luke Skywalker).  At night without the sun, the lack of humidity in the air allows the temperature to fluctuate dramatically.  Temperature fluctuations in smokers are never a good thing. 

Third is the piece of metal that I installed on the irebox side.  It is simply a 12" x 24" sheet of 22 guage steel (cost me about $12).  I bent it across at the 6" mark and gave it an angle that made about a 4" drop.  Since the cooking grate will be positioned in line with the top of the heat source, I wanted to deflect some of the hot air coming right at the meat.  This way I have a bit of radiant heat coming off of the steel, but not too much directly on the one side.  I have access to some bending tools, but if you don't, you can also accomplish this by screwing down a 2x4 over the top of the piece of metal, and then using another 2x4 shimmied underneath to lift and bend.  It doesn't have to be perfect by any means.  As a side note, I also washed down all the steel parts with dish soap and a big sponge.  Most of the steel you will buy will have a light coat of oil on it to keep it from rusting in the store.  I didn't want to eat that and dish soap is great for taking that off.  All of your metal should rust within a day or two (unless it's stainless).  Otherwise it isn't safe to eat off of.

The last thing in this pic is the rebar going across to support the cooking grate.  I ground a lot of it off with an angle grinder since it seemed to have some sort of coating on it.  Even though it was weld steel rebar, I just wasn't comfortable not knowing what the coating was.  Depending on what size you get (these were 48"), you will need to cut the rebar.  Again, this can easily be done with an angle grinder or circular saw with a $3 cutting disc.  If you don't have one, your neighbor probably does.  Invite them to the party. 


Another view of the pan and deflector from the inside of the cooker. 


To get the rebar to sit flush with the top of the block, you will need to chisel a small notch out.  I did this easily with a simple hammer and chisel. 


.....more to come.  I have to get my day started.  Keep the comments coming. 
I got a sheet of expanded metal for about $85 and cut it down to 80" long.  I left a little on the one side to act as a shelf for my thermometer. 


On the side away form the firebox, I cut a block in half and placed the cap stone on the bottom. 


Then I finished the block laying with capstone all around and the block on top.  THis lines up the vent with the top of the entire structure.  I chose to put capstone on top of everything to limit the chimney effect and increase the insulating properties of the air in the structure. 


Now for the top:  I have seen many people use things like a regular sheet of plywood, galvanized sheets of metal or a single sheet of roofing tins.  These all have their drawbacks that include a lot of heat loss, pine sap and glue leaching into food and poisoning of your friends and family.  I really didn't want any of the above, so I came up with a bit of a radical design.  Basically, I made a plywood structure filled with rockwool.  Similar to the perlite, rockwool is an inert insulator that is made from volcanic silica rock superheated and stranded out into a wool like substance.  It won't burn and won't give off any chemicals, but it sure does insulate.  I am pretty conident that I will have almost no heat loss out of the top of this thing.  The one drawback is that it is a bit heavy.  It eally doesn't bother me, but if you are looking for something lighter, I would try and cut down on the dimensions. 


I still had the problem of the plywood being exposed to the food.  I didn't really want my pig tasting like glue and pine tar so I got a heavy piece of aluminum and bent it to fit around the boxes on the top.  This way, the only thing that is actually exposed to the food is the aluminum.  If you have concerns about using aluminum, I will say that I won't use it in the firebox, but if you can name one person that you know who doensn't cook with aluminum foil, then I will be very suprised.  If you really have concerns, then you can obviously use a sheet of steel instead.  This would have been the full width of the top, but I got this piece donated and it was a cut off.  You can see from the lower picture that it works perfectly. 




Here's a pic with the top on the whole thing.  I butted the two pieces (which were 48" x 40" each) together and added some hinges in the middle and a handle on each side to open and close the top.  I also put some high heat paint on the top to protect the wood. 


Man.. Thats awesome... will be keeping an eye on this... Let me just say a few things...

1. I'm glad you didn't mud the blocks together
2. reason being.. your blocks are just regular concrete blocks.. they will crack and break from the heat... so not cementing them in is a good thing as you can change them out as they break...

waiting to see how it works...
OK I get it now. Firebox had me confused. If its stable no need to mortar blocks you would need fire cement anyway & that stuff costs.Are they just normal bricks under ? They will hold heat OK..Again refractory bricks cost but are great holders of heat. So I  figure its the off set principle same as the units I see built on the forum.Not done this end of the world.Makes it all the more interesting.
I agree with all the recent comments.  If I was going to make this permanent, refractory cement would be the way to go.  I would most likely just mold the walls.  I would also be comfortable lining the majority of the inside with brick, like I will be doing for the firebox.   I have a few extra blocks on hand expecting that I will lose a few.  I would probably also do something decorative on the exterior.  River stone or something. 

Can anyone comment on the clearence please?  I have 12" right now and am planning on an 80 lb pig right now split open.  I really don't know what the height I would need for that size pig would be.  I figured that once I got the pig,  it would be easy enough to go out and pick up a few more blocks from HD and put them on top. 

I have some more pics coming.  I may be making a full steel top and door for the fire box, so I am waiting to see if I can make that happen. 
Yes Cowgirl is an expert when it comes to concrete block cooking.  One thing she mentions is to use stainless steel for the grate.  I totally agree but wanted to give you an idea of what the prices were.  I paid about $85 for a regular expanded steel sheet at the guage I was looking for.  THe stainless version of this was almost $500.  If you are making this a permanent structure, I completely recommend it though. 
I also wanted to keep more heat in to smoke the pig instead of just roasting it.  It doesn't come into play "as much" when you use direct heat, but with the offset design, I needed to seal the box a lot tighter.  THat's where the top came in. 
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I am enjoying this thread, and your build looks fantastic. I have also been researching whole hog pits for my first whole hog smoke on May 19.

It seems like the biggest cautionary advice experienced folks can offer is to keep the fire away from the pig and the dripping fat. You seem to have solved that problem with your offset design. I look forward to seeing how it performs.

One thought I had was to keep the coals smack dab underneath the pig with some type of shield between the pig and the coals, slightly smaller than the pit so the smoke and heat flows out from under it and up the sides of the pit -- a sort of tuning plate, if you will, or an oversized plate setter if you speak "Big Green Egg-ese". That way the shield provides the benefits of indirect and even heat distribution as well as catching the fat drippings, keeping them away from the fire. Then the question becomes what type of material to use? A fairly heavy guage steel, I suppose.

Anyway, that design most likely will not happen before May 19. I will probably go the way of those who went before me and put the coals at the ends or in the corners of the pit. It will be good either way.

By the way, your pit cover is a work of art. I was considering ceramic blanket material sandwiched between two pieces of tin roof metal. But all of the tin roof suppliers around here only carry galvanized products.

I will definitely be following your build. Good luck.
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Thanks everyone for the great comments on this.  I finally fired this beast up today and boy was this a challenge.  I have read elsewhere that these things can take a while to heat up.  Basically because you are heating up a lot of real estate:  the concrete, the top, the ground, etc.  It took me about 6 hours and 50 lbs of charcoal just to get this to a good and stable 250.  I began conservatively, thinking that I was going to completely overheat the thing, but by the end of my play time, I was dumping the whole bag of coal in at once.  I went through 3 sacks of wood chunks as well just to get a bit of smoke through.  Since the chunks aren't smoldering (like chips do in a box), I was unimpressed with the amount of smoking I actually saw happening. 

So this is where I need some assistance/advice:  I was able to get this well heated and stable (even though it will take a whole heap of charcoal to do this).  What I wasn't completely happy with was the flow of smoke throughout the cooking chamber.  I am attributing this to the lack "breathing" that the cooker had.  I just didn't see the convection currents flowing out the vent as much as I feel that I should have.  Now I understand that I only had this going long enough to get it up to 250 and maybe I needed it to be burning a bit longer to establish this flow....sort of like warming up the flue on any chimney.  Can anyone who has experience with the larger cookers give me any pointers on this? 

What I did try this time:

1. Put a small fan in front of the intake on the fire box. 

2. Adjusted the opening on the firebox (found that the smaller opening of approx 8" x 8" worked best. 

What I currently plan on trying:

1. Getting a fan for the exhaust to "pull" the air out and help it along until it gets a good established flow. 

2. Using logs to smoke.  I figure that this will cut down on the amount that I need to continue adding chunks, instead of every 10 minutes. 

3. Get rid of the steel baffle.  I assume that this may be hindering the air flow more that I thought.  Since I am actually having trouble keeping the heat up, I don't see the need for it.

4. Getting another thin piece of steel to better seal the transition between the main chamber and the firebox. 

Any and all advice is appreciated.  Thanks in advance everyone. 

PS....the chickens that I did in this thing came out amazing.  My mother was extremely pleased for Mom's Day.   
staredat, morning....  Try this concept.....  On the exhaust end of the smoker, add 2 each 90 deg elbows that fit into the holes of the blocks and add chimney extensions to the elbows.... 

(probably 5" elbows) ..... Maybe start with a 3' section on each elbow and have another 3' section ready for each depending how the draft works...  plug the space around the elbows with rock wool or something to seal the space and the draft "sucks" better.....  I'm thinking a dual 5" x 6' chimney would work to start.....   Just thinking......   Dave 

Also another thought, lower the block that is the exhaust block to grate height....  most side firebox smokers have the exhaust stacks at grate height.... the height of the chimney provides the convection flow...  
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