Repairs/Questions on Large Masonry Offset Smoker

Discussion in 'Wood Smokers' started by pianov, Sep 26, 2013.

  1. I belong to a group that has some land where someone built a large wood-burning offset firebox masonry smoker. I think the smoker was built only about five years ago. The build is of high quality, but there are some design problems. I think the original design had some sort of grill (wood? charcoal?) above the fire box in addition to the smokebox.

    Here is a link to a bunch of pictures of the unit: Smoker?sort=3&page=1

    A gas grill was built separate from this unit, so we no longer have any interest in the original grill portion of this unit. As you can see in the pictures, the grill thing is now just a pit about 11 inches deep. The bottom of the grill pit is the ceiling (warped 1/4" plate steel) of the fire box.

    If the fire box is adequate (see below), my first question is how to best repair the top of the fire box. The 1/4" plate steel ceiling of the fire box is warped upward in the middle about one inch. Seems to me the best thing to do would be to seal that gap off somehow. Would fire-brick mortar be the best thing to seal it with? It is warped on both sides, so it would have to be sealed to the steel plate on the right that overlies the opening to the smoke box, and on the left side where the steel plate ceiling butts up to a masonry wall.

    And then how to finish the top off? Just fill the 11-inch-deep pit with bricks and mortar and maybe topped with three or four inches of reinforced concrete (and maybe tile on top of that)?

    And then that leads me to my other major question - is the fire box large enough? I've read that a fire box should be a minimum of 1/3 the volume of the smokebox.  The volume of the firebox on this smoker is about 7% of the volume of the smokebox. Is there any hope of this fire box working properly for this smokebox (I have not yet done a burn with this smoker)?

    The smokebox measures 49" wide, 41" deep and 99" tall = 200,000 cubic inches

    The firebox measures 24" wide, 45" deep and 13" tall = 14,000 cubic inches

    I wonder that because the firebox footprint is 24" X 45" = 1,080 square inches and the smokebox footprint is 49" X 41" = 2,009 square inches, perhaps the size of the firebox really isn't so terribly small being that the footprint of the firebox (which means the SIZE of the fire) is a little better than 50% of the smokebox footprint. Keep in mind also that this is a masonry smoker - good heat retention - and the fact that this smoker is in central Florida - the coldest weather we'd likely ever encounter during a smoking session would be about 60 degrees outside - so it's not like we need a humungo fire to heat up a below-freezing smoking chamber.

    But then again, that IS a VERY short height for the fire box - yes? I built a much smaller masonry smoker at my home of similar design (offset firebox) and the interior of my firebox is 21 inches tall - almost twice as tall as the subject very large smoker. How will the short height of the firebox affect it's performance?

    A third, directly related question is this: if the fire box height is a problem, as long as I need to repair/redo the top of the firebox, I could just get a bit more radical and tear the existing top apart and make the firebox up to 11 inches taller - I could make the firebox a total of 24 inches or so tall. If I were to do that, what is the best construction for the top of the firebox? Would a heavy steel plate be the best thing (maybe 3/8" thick)? I guess I would want to also move the opening between the firebox and smokebox from where it is at the floor of the firebox up to the uppermost area of the firebox (and probably make it smaller - well, size it according to the calculator this site has).

    Lots of questions. Hoping for any good input. I think this smoker has a few current problems, but that it also has EXCELLENT potential. Really looking forward to some input. Thanks!

    Terry Farrell

    Tampa Bay, Florida

    FWIW: I am not a super-expert smoker guy. I built my masonry smoker at my home about 20 years ago and have been smoking mostly pork on it ever since. I'm very happy with the performance of my smoker and have gotten some good experience with it. I have had to make a few small modifications to it over the years to improve air/smoke flow, etc., so I have gained some experience with those issues also. I'm really looking forward to my first smoke session on the subject BIG smoker!  Here is a link to a picture of my smoker at my home: Turkey/P4150009.jpg.html?sort=6&o=1
  2. One other thing I neglected to ask about the fire box on this large masonry smoker: The interior of the fire box is six courses of brick tall. Only the lower four courses of brick are fire-brick - the top two are just ordinary red bricks. Is this thing going to just crumble to bits after a few good long fires? Or is it the case that only the brick right next to the burning logs (like maybe only four bricks tall!) really need to be fire brick?

    If I were to make the fire box taller, would I need to line the new upper part with fire brick? And finally, if I am going to that extent, and the existing top two courses of red brick are a problem, should I just tear out the two courses of existing red brick and replace with fire brick - then I could have a 24-inch tall fire box completely lined with fire brick.

    And regarding the top/ceiling of the fire box. I mentioned making it out of 3/8" plate steel. I'm pretty sure that would work well. Is there any advantage to building the top out of fire brick supported by angle iron?

    Thanks, thanks and thanks. Sorry for so many questions - but that is the reality!
  3. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Terry, morning.....  I would use the smoker as is, with the exception of replacing the top of the fire box with a steel plate that "floats" to allow for expansion....  You do not want to heat the smoker up fast, or get it too hot...  a small fire tended for 24-36 hours should be adequate to heat the smoke house up to operating temp...   Getting any part of the smoker over 225-250 deg too fast could cause spalling of the bricks and destroy the smoker.... 

    Personally, I would use it as a cold smoker to a warm smoker avoiding temps over 200 deg....   whomever built it, knew what they were doing when it came to brick laying....

  4. "...replacing the top of the fire box with a steel plate that "floats" to allow for expansion.... "

    And I'm pretty sure that's why the original steel plate is warped - it expanded, butted up to the bricks, and then because it couldn't expand any more, bent/warped upward.

    But are you suggesting to leave the steel plate where it is now for a 13-inch tall fire box, or to move the top of the fire box up to the very top of the fire box structure (the original "grill" height) for a 24-inch tall fire box? Is 3/8" plate steel the "best" thickness?

    "You do not want to heat the smoker up fast, or get it too hot..."

    Specifically why is that? Are you speaking only of the fire box because of the lack of fire brick? How hot is too hot?

    "...a small fire tended for 24-36 hours should be adequate to heat the smoke house up to operating temp...   Getting any part of the smoker over 225-250 deg too fast could cause spalling of the bricks and destroy the smoker...."

    What is "spalling of the bricks"?  I do most of my smoking on my home smoker in the 220 degree range. But every once in a while a fire has gotten away from me and the smokebox has jumped up to 300 or 350 - and a few times even stayed there for a couple hours - I've never noticed that it caused any trouble with the bricks. But maybe that doesn't really matter as I would never be intentionally smoking at more than 250 degrees anyway.

    Thanks for your input.
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Spalling can occur from heat or freezing...  It's the trapped moisture that raises havoc....   

  6. "I'd leave it where it is for now... Float a 3/8" plate...." 

    Don't think that will be possible with the current size FB. The 1/4" warped plate that is in there now clearly was placed where it is and then the rest of the top was built over it. The back side of the existing plate is overlaid by a massive 12" by 12" (or larger) brick/mortar structure - I don't think it can be removed without destroying the rest of the top (area where the grill was and to the rear of that). So that means leaving the existing plate steel FB ceiling where it is.

    Now what is the best way to seal the one-inch gap where the steel plate has warped upward? Perhaps just jam some kind of high-temp insulation in the gap? Any suggestions on what to use? Any better ideas?

    Thanks again for your input.

    Terry Farrell
  7. I see what you mean about spalling now. Never saw that before. Perhaps it won't be a significant concern in our case as the smoker is in central Florida - so no cold temperatures, and the smoker is under a roof - so it never gets wet.

    But we'll be gentle with it anyway....
  8. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Fill the gaps with Red Devil stove cement...  It will act as a filler and sealer, and it hardens also... 

    Fireplace and Stove Silicate Sealant is non-flammable, silicate-based compound that sets rock-hard when fired. The black textured paste cures with a warm fire and provides a durable, long-lasting seal that withstands temperatures up to 1000°F.

    Adheres To:

    Concrete, Cinder Block, Stucco, Stone, Mortar, Brick

    Use On: 

    Fireplaces, Wood-burning Stoves, Flues, Concrete Ovens, Chimney Joints, Ash Pit Doors
  9. Excellent. Thank you.

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