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Offset Concrete Block Hog Smoker - Page 2

post #21 of 39
Thread Starter 

Thanks Dave.  So just to be clear on this:  If I devised a chimney/exhaust, that would help create more flow (sort of like a siphon with the convection curents)?  instead of just having the open block?


I have already moved the exhaust block to the complete bottom of the cooker at the advice of a local guy who sells some of the big cookers.  His theory is the same as yours.  But I think that might be too low.  If I raised it to the height of the grate (as you mention) should I choose the block just above or just below the grate?  The grate is sitting between two of the blocks. 


I was just in HD looking for an inline exhaust fan as well as some of the fiberglass rope.  I can see from the smoke marks where I may be losing a lot of the heat since it really is trying to just get out the top.  I am toying with the idea of skim coating the top layers of block with concrete just to seal them a bit as well. 


After looking at where most of the smoke went yesterday, I was wondering about the size of the threshold that the heat need to get across to get to the main cooker space.  I have about 8 inches that it needs to pass over vs most of the other cookers where it is significantly less.  I may remove the intake blocks, support the ones above with rebar and then be able to slide the firebox a bit further into the cooker itself. 


I was really amazed at how much this took to warm up and am thinking about making a smaller seperate firebox with lava rocks where I can run a 60K btu gas burner just to warm up this thing.  I did some calculations and it may actually be half the price to warm it up with gas then bring in the other firebox with charcoal for the actual cooking. 


Keep the advice coming folks.  I really truly appreciate it while I work out the kinks of this beast. 

post #22 of 39
ok then.. that was a good learning experience... The things that I would try are... (first I'll have to renig about sealing the blocks in an earlier post)... I would try to seal just the joints with some heat resistant cement... Also I would do the top of the block with stucco as you mentioned but would go further and lay a piece of plastic on top of the very wet, thick stucco and place the lid on top while the stucco is wet and push the top done into the stucco to form a trench (so to speak) for the rail on the underneath side of the top to sit down into when dry (plastic is so the top won't stick to the stucco and should come off after dry).. hope that made sense... next I would use just a half block for my exhaust vent turned sideways ON TOP of the grate.. maybe use the pit calculator to figure out the size of the exhaust vent... If the single half block isn't big enough, use 2 half blocks... one towards each corner instead of both together... do the elbow and stack deal as Dave mentioned and seal around the elbow in the block with the cement... The calculator should also tell how tall above the pit your stack should be... with a stack ,the breeze blowing across the top of it will create suction up out of the stack... calculator should also tell you what size your hole from the firebox to the chamber should be... I would also try to bring things up to temp (preheat) with a big wood fire instead of charcoal (sounds cheaper) and then maybe keep temps up with the charcoal... those are just a few things I would look into before my next excursion...
post #23 of 39

staredat, evening.....  Sorry about the late reply....    Before sealing the blocks, try it out....  Heating the cooker will take quite awhile, there is a lot of thermal mass there to heat up....   I'm also thinking maybe cover the fire pit with cap stones.... the heat will only have one way to go then....   Also about chimneys.... It's the nature of the beast that they "have to draw"... once the height is there, the  atmospheric pressure difference top to bottom makes them draw... A little heat will get the draw started... crumple a paper, light it on fire, put it in the chimney at the bottom.... Instant draw....   looks like once you have a fire, the bricks get warm, the chimney starts to draw.....  MILLER TIME and COOKED PIG .....   Have you figured out if you will have to rotate the pig end to end and how ????  if necessary.... just thinking....maybe a separate rack to hold the meat on the main rack ???  

I think your cooker is a great idea and hope it works for you.....  Dave

post #24 of 39
Thread Starter 

Jack:  Love the idea of the stucco on top.  Completely understood the plastic cover.  I was actually looking at the fiberglass rope to get a better seal, but it is extremely expensive.  This would definitely smooth out any small variations.  I have tons of wood and will use your suggestion about preheating with just a wood fire.  It would be much easier to take my time and add a few logs for hours on end instead of wasting tons of expensive charcoal to ge this sucker warm. 


Dave:  Will definitely try out the chimney.  I can see how a simple thing like getting some burning paper for heat would start a good convection current.  I didn't put the final pics in, but I have 1/8" steel on top of the firebox.  I warped that pretty good this weekend, and may just go out and get myself a 1/4" piece.  The piece I have isn't bad, but I have to keep blocks on the corners to keep them form curling up.  As far as moving the pig, I am starting out with 100 lb'er.  I have a few humongous trays that I think I can manuver this thing around with.  Ultimately, I am trying to get my brother to weld me a square with handles that the expanded metal is attached to so that that entire cooking surface can be picked up and removed by 2 people.  I probably won't have it complete for this party, but will begin working on it immediately afterwards. 



Now I have to decide on one chimney or two.  I can't wait to fire this thing up again.  It's definitely going to be a good challenge and learning experience.  I am truly amazed at how significantly different this thing is vs my GOSM (I know I know....totally different), but I feel like this is a good training ground.


I will get some more pics up asap and will be heading to the hardware store tonight to figure out the vents. 


I have avoided all galvanized metal up until now because of the poison off-gassing, but should I have the same concern when using it just for the vent since it is all past the cooking chamber?  Most of the duct pipe I have seen is galvanized.  Thanks again everyone.   

post #25 of 39
my opinion on the galvanized is to use it..... It's on the exhaust end and it WILL NEVER see the temps need'd to gas... plan is sounding good so far
Edited by JckDanls 07 - 5/15/12 at 5:13pm
post #26 of 39


post #27 of 39
Originally Posted by staredat View Post

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. 


Actually, I said  "After placing your foil and drip pans in the bottom, lay the grate across the blocks. Stainless is great, but any grill works good." biggrin.gif 



Nice job on your build Staredat! ...and Thanks!! biggrin.gif


post #28 of 39
Thread Starter 

So I accomplished my mission here. THanks for all the help form everyone. I truly couldn't have done it without you. Sorry it took so long to update this, but I ran off to Mexico right after the BBQ (that's one way to avoid negative crticism).


I took your advice and installed a 5" vent pipe. I think it's about 5' high as well, whatever the standard length I got form HD was. It immediately began to pull the draft right across cooking surface. I used maple logs to heat the cooker up over about a 5 hours period. I then went to a mixture of gas (only because I was deleriously tired after being up for 24 hours) and charcoal with pecan and hickory logs for flavor.


The pig was 105 lbs and was injected with a mixture of molasses, apple cider vinegar, bourbon and spices the day before and again just before cooking. I rubbed everything the day before as well with two different rubs. It cooked for about 12 hours and was absolutely delicous. THe middle acted like a big bowl and just collected all the fat and juices which we collected and used to dip all the pork in. It was also really interesting getting the pig to the backyard from the cooker. I will hopefully fabricate something soon that is a more manageable and removeable grate, but we basically had to deconstruct the majority of the cooker and have 6 people assist with the "funeral procession" of the pig.


I didn't flip or turn the pig at all. I had the hams towards the fire side and the whole thing cooked nice and evenly. I can't wait to do another soon.


PS...the pig looks a bit dark but it was perfect bark on everything. I put bacon on top of the loins after about 5 hours.


THanks again for all the help. 



I only used one and capped the other with aluminum foil.  I fille din the gaps with concrete. 





funeral procession






post #29 of 39

Staredat, morning and congratulations on the success of building a great hog smoker and success with the pig.... It sure does look good... I'll bet you are the go-to-guy for cooking hog now....  Other low and slow cuts of meat should do very well on your cooker.... Keep us posted on your future Q's ....   Dave

post #30 of 39
This is all great information. I will continue to follow. I hope to start drafting mine up on Monday for whole hog event on July 7. Thanks for sharing!
post #31 of 39

Hey there,


Any other mods since?  I am getting ready for whole hog #2.  My daughter's first birthday hog was such a hit with family and friends we are doing it again.  I am planning on making some mods to my block pit.  I need a good lid, other than the piece of old ply I have been using.  I am not sure about the one you made, but I will look into it.  I have seen folks using cement board.  Placement of the exhaust vent?  How low did you go?  How tall for the stack?  did it make a difference?  What about fire brick in the pit?  I do not know how expensive it is or how hard to find.  But I figure it can help hold the temp.  I am going to go back in the thread and check, how big is your firebox?  I have a few more questions, but I am going to go back a look again before I ask.  Thanks for all the pics.  I will try and post more of mine this year. 

post #32 of 39
Thread Starter 

Hopefully I can answer all the questions, although I am away form my pit right now so will have to double check on a few of these:


1. Any other mods since?


Nothing major, but I have been playing with the placement of the vent.  Once issue with this design is getting the heat to evenly distribute from top to bottom.  It distributes nicely across, but I have abiout a 30 degree difference between the grate and the lid.  Not terrible, but I would still like to improve that.  IN an attempt to do that, I dropped the vent to below the grate to allow the heat to build up and reverse back on itself a bit.  Optimally, I would like to get a steel plate and turn this into a reverse flow build which was the original design. 


 2. I need a good lid, other than the piece of old ply I have been using. I am not sure about the one you made, but I will look into it. I have seen folks using cement board.


The lid I have is great at holding in the temp, but you need to have a metal bender.  I had access to these at a local shop.  The thick aluminum keeps any contaminants from the ply out of the food.  The rockwool/mineral wool is a great insulator that is used in commercial smokers and is completely chemically inert.  If I would make mods to the cover, it would be to make it lighter.  Use 1x3's instead of 2x4's and thinner ply.  I used 3/4" and overall, the cover is a beast, but I am barely losing any heat.  The combination of the rockwool and poorly conducting wood works well. 


3. Placement of the exhaust vent?


I have been playing with this a bit.  WHen I did the pig in the pics, it was placed right at the level of the grate and the pig came out perfect.  I did another one when the vent was just below the grate, and that also came out nicely. 


4. How low did you go?


Related to temp?....I kept it around the 230 degree mark. 


5.  How tall for the stack? did it make a difference?


THe stack I have there was the standard 48" (I think) vent pipe.  THe diameter is about 5" and is plenty for the smoker.  I have a baffle in there that I can close almost completely to control it.  I would say it doesn't need to be this high to get the flow you need.  All of this is available at Home Depot. 


6.  What about fire brick in the pit? I do not know how expensive it is or how hard to find. But I figure it can help hold the temp.


I just used regular brick.  THe concrete is what you need to be concerned with cracking.  Even regular brick is already fired at temps much higher than what you are going to encounter in the fire pit here.  It does help hol the temp a bit, but mostly I wanted to insulate the concrete block form the temps in the fire box. 


7. how big is your firebox?


Not big enough.  THis is the one mod that I need to work on more.  The current box only has internal dimernsions of 24" wide x32" long x 16" high. It's a bit hard to calculate hte size needs for a firebox with a concrete block cooker using traditional methods.  Since most steel cookers are calculating jsut the internal size fo the cooker, that's all that you have to account for.  However, with this, you have to consider the fact that you are also heating the thick walls of the cooker.  The length is more than enough, but I would mak the box a bit wider.  It would require a mod to the opening as well to get the heat right in there.  If I get around to making the reverse flow concept, I will have to put some pics up.  To save on money and time, I have used a 60K btu burner from my crawfish cooker that I will jam in there to preheat the cooker.  I will usually turn that up good and high and llow it to run for about two hours before I even start with the wood and charcoal.  The $16 refill for the propane was much cheaper than the multiple bacgs of coals that I used to previously warm the body of this cooker up. 


Hope this all helps and let me know if you have any other questions. 

post #33 of 39

I don't know how I missed this post. Great job! 

post #34 of 39

Thanks again.  I think I have all the mods figured out.  The how low question was related to the question of where to place the exhaust pipe relative to the ground.  I am going to increase the size of  the smoking chamber and the firebox.  I plan to heat the pit up with wood prior to coals and such.  I though about using the propane cooker, but the wood will work, plus I can grill something up while heating it up.  Then I will maintain temp with charcoal and wood chunks for smoke and flavor.  I am going to use sand in the fire pit floor instead of brick.  Maybe someday.  Last year it went really well, so I am hoping for good things this year.  I feel like I have a better handle on it.  Plus, I am not starting at 2am like last year.  I am going to put the pig on around 11pm or midnight.  I was so worried last year, I barely got any sleep.  I have more help this year and I don't feel the need to wake up every hour.  I will post pics and of course some QVIEW.  I was bad about that last year.  I only got some finished shots.  I will take some before and after pics of the mods.  Thanks for everything.  It really is a great way to celebrate with friends and family!  Plus a great way to flex your CUE muscles.

post #35 of 39

The build looks great, I just poured a 11 ft by 8 ft pad yesterday, getting ready to build a block smoker.

thanks for info.

post #36 of 39

Hi Staredat,


I built a block smoker earlier this year (different design than yours) and so far have not had a brittle block issue. Note i say so far.  I did burn my wood roof off- it smoldered all night and the blocks on my top course were brittle.  You will know your blocks are bad if you started with the regular grey color blocks and they sort of look a salmon slight pink color- and you can tap a screwdriver into them and they just chip apart- with little effort. If you drop them they just fall apart.   I have probably operated my smoker http://www.smokingmeatforums.com/t/135937/block-smoker-build-in-mi  say 15-20 times if you include dry runs and so far the blocks are holding up-  i do tap them every now and then just to check.  Glad you filled with perlite- i used batt insulation... before i knew what perlite was;)


Jealous of your first hog btw ;)

Originally Posted by JckDanls 07 View Post

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...
post #37 of 39
Thread Starter 

I feel like I've neglected this post, but thanks for all the great comments and praise.  I think I am going to have to do a labor day hog now just for the heck of it. 


@Cityofvoltz - I agree.  No problem at all with the blocks splitting, especially since I have a few bricks in between the wood box and the block.  I only used 1/4" steel on the top and that's starting to warp a bit.  For $50, I can get a 1/2" plate to replace it, which I always intended on doing anyhow. 


@smokinbrew - lemme know how it turned out.  I would love to see some pics.   

post #38 of 39

great hog

post #39 of 39

That was an awesome build. Want to do one alongside my wood fired pizza oven. Thanks for posting your build as you have done most of the groundwork.

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