39" Pompei build in NH

[Gulf]

I agree with Mike on the formula. The Type N mortar that you will be making from scratch is far better than buying the labeled Type N bagged masonry cement from the building supply store. The stuff they sell nowadays has too many proprietary ingredients (IE: crushed limestone) for the lime portion of the formula. We used to make it from scratch for fireplaces and BBQ pits. The old school mortar would last 30 years before needing to be re-pointed in the fireboxes where it received direct flame impingement. The Type N masonry cement that you would buy already blended will swell and pop the faces off of firebrick in a firebox.

All that being said, the back of the flue, just above inner arch, receives an extreme amount of heat. The front, not nearly as much, because of the ambient air that is being mixed in with the exhaust gasses from the dome. I don't like mixing different types of mortars on the same course. So, my advice is to stay with the home brew for the vent and flue. If not, thirty years is a long time .

[ML38]

Thanks for the replies and recipe recommendations. I appreciate the expertise

Well........the dome is closed!!! A lot of cuts to make the keystone see the pics attached. First pic is the large brick I used before and second is the after. Once I got a good look at the interior while cleaning it out I realized there are quite a few joints with no mortar but I had to have my head inside to see them so no worries I guess.

On to the vent!

[SableSprings]

Nice to have the keystone in after all the sweating and cutting. Looks good and those joints all have mortar, just not enough to come out and say hello. Your build will perform properly and last well past your craving for pizza! You definitely have earned a nice, cold adult beverage to sip as you sit back and admire your handiwork (and contemplate the next phase of the build ).

[ML38]

You definitely have earned a nice, cold adult beverage to sip as you sit back and admire your handiwork (and contemplate the next phase of the build ).

Mike,

I have to admit to some really poor planning because after finishing the dome, ther was not a cold adult beverage in the house.


Back to the mortar question I had earlier, is it a problem to use my homebrew 3:1:1:1 recipe for the buttress. It would help to not have to mix two kinds of mortar since I'll be building both the entrance/vent and the buttress on each side as I work my way up.

Thanks
Marc

[SableSprings]

Bummer about the poor planning yesterday Marc...but there's always today and tomorrow

Go ahead and use the homebrew for the buttress and the rest of your brickwork. You have the materials already, it's a good mix for compression and flexural strength. More importantly, you are now very comfortable making and using it

Keep posting photos of your progress for us.

[ML38]

One progress pic showing my raised up hearth in prep for the granite counter that will extend 18 inches out from the outer arch out onto the granite extentions and some dry placed bricks to check on how I want to build the buttress.

Measured my dome height this morning and if I count the 1/4 inch because the keystone didn't come down flush to the rest, my height is right around 20 3/4 in. My door height is 12 5/8 give or take so I'm looking at just a bit over 60% so I didn't hit the 63% target but it turned out within an acceptable range I think.

Hopefully get some vent done this weekend.

[ML38]

Had a pretty productive weekend. Finished the entry walls and front arch and the buttress work on each side. Just have to figure out the vent to flue transition now. The opening is 9 inches wide right now. I think I should add another internal arch that will close it to 7 or 8 inches and also bring up the height to match the front arch so it will be easier when I have to transition to the chimney. My door jamb is a little narrow but it was kind of unavoidable.

Progress pics:

[ML38]

I added an internal 'arch extension' for lack of a better term and finished out the front arch corners. Also test fit the granite counter top. I need to narrow it to about 17" so I don't have to reach so far into the oven. I'm going to use the trimmed portion to add a shelf to each side of the entrance (see the space in the pics on the last post. I've decided I'm definitely not going to be a mason in a second life.

Question on transitioning to the flue:

My plan is to cut some bricks to flatten the tops of the arches. I have some 9 inch square bricks that I was hoping to use at a 45 degree angle on each side. I'll put some angle irons across from one buttress to the other to help take the weight of the brick chimney I plan on having.

Does this sound like enough support for a 6 foot brick chimney? I also plan on a pergola that the chimney will have to go though which is why I'll need 6 ft

pics

[SableSprings]

On your first picture in post #22, it looks like there are spaces behind the front buttress bricks. Is that a space that will be filled or is it just an illusion? If it's a space, being an over-achiever , I'd put in a couple sticks of rebar that lean toward the chimney and then fill it with left-over brick pieces, mortar, and/or concrete to make it solid. With the current layout, I think you won't have any problems with a 6 ft chimney. I'd hedge a bit and buy the common brick (with the holes) to reduce the weight (and beef up the buttress space if it exists ).

Your idea of using some bricks cut/ground to make a flat platform on top is a good one. If you take a grinder to the outside arch edges and make it have a little curve up, you'll have much better flow of smoke up and into the smoke chamber/chimney. Remember if you use rebar in an area where there will be significant heat, don't mortar it in tight and leave a little space on each end of the iron. That way if the heat makes the steel expand, it slides instead of rips up attached brick & mortar. I did a similar thing with angle iron across the back of my arch to create a gap for moisture escape from my dome's insulation layer into the nested flue tiles I used for my chimney.

Make sure on your pergola plan that you align it so the chimney goes between the beams on its way out...one of my issues in the Dragonfly Den. If you plan on a waterproof roof for winter, that alignment and available options for flashing with the alignment will become pretty important...again, lesson learned here.

Looking good!

[daveskis]

Very nice.......don't forget the beer

[ML38]

I'm all stocked up on beer for the next milestone!!

Question on flue size:

I have access to some reclaimed clay flue pipe. it is 8" outer dimension and 6 5/8" internal square.

I like free things so if a 42 in oven recommends 8" round and 36" recommends 6" then is it correct to assume that my 39" oven is good with 7" round (38.5 sq in area)
therefore this flue with 42"+ sq in area will be good? .......and free!

Thanks
Marc

[daveskis]

Hey Marc I have used 8" stainless. I get some smoke out the front when lighting as I guess does everyone else. But look once the fire is going I'm talking a couple of hours later. This is when it is too hot to keep your hand in the vent. It wont smoke at all. Its just hot coals.
Others here will give you fancy formulas for the size of the oven V vent size and so on. It can be as complicated as you want. Free flue, just use it mate.

[SableSprings]

Marc, my oven is 39" inside diameter and I had a similar question. I bought 8" ID square clay flue pipe (walls are 1" thick, so I've got basically a flue that's a bit undersized by the book). I did make an enlarged smoke collection area leading into the flue and for the early part of the firing, I do get some occasional "puffs" of smoke out the front. Once the flue heats up however, it draws just fine.

My biggest mistake is that my outside arch is about the same height as my inner arch. I think if I would have lowered the front arch just an inch or two, I would not have any smoke pop out on startup. Since your round clay flue actually has thinner walls than mine, your larger 7" ID (and 43 sq inch area) should draw like a champ.

As both you and Dave noted above, free is good ... but I'd bump that up to "Free is GREAT!"

[Toomulla]

Marc, my oven is 39" inside diameter and I had a similar question. I bought 8" ID square clay flue pipe (walls are 1" thick, so I've got basically a flue that's a bit undersized by the book). I did make an enlarged smoke collection area leading into the flue and for the early part of the firing, I do get some occasional "puffs" of smoke out the front. Once the flue heats up however, it draws just fine.

My biggest mistake is that my outside arch is about the same height as my inner arch. I think if I would have lowered the front arch just an inch or two, I would not have any smoke pop out on startup. Since your round clay flue actually has thinner walls than mine, your larger 7" ID (and 43 sq inch area) should draw like a champ.

As both you and Dave noted above, free is good ... but I'd bump that up to "Free is GREAT!"

if you lower your outer arch how will you fit a door

[UtahBeehiver]

The key to this question, because I did it, is that the outer edge of my revel on the door is smaller than the outer radius of my outer arch. I have a large brick revel on the inner arch and inset the out arch to act a air dam so smoke would take the path of least resistance, the chimney. As you can see I do get some smoke staining out the front but this is primarily at a cold start up. One the oven starts to heat there is no smoke unless I overload the oven with wood or a green piece sneaks in there. FYI, this is a 42" ID oven and I used a 7" ID double stainless steel chimney but i did have to add an additional foot to get a proper draft.