36" Corner Build in Minnesota

[RandyJ]

Do not bother with angel and beveled cuts both. In my honest opinion just do beveled cuts as you get higher in the courses. The amount of work required to do the other way is incredible and a tiny error will cause huge problems. Also no one but you would know anything different and it will not look any different from the inside. If I built a 2nd oven i would not even consider the more difficult way. I didn't even build a jig when i built mine. I just used shims and the cutting sled on my harbor freight saw. Also mrchipster used a 14" saw and that would be necessary to make all the cuts with the jig i believe. A standard 10" blade is not big enough.

I cut my floor to fit inside the dome so i don't have any insight as to how to make that work. I had used a strip of cardboard as a spacer for expansion and contraction. I hope some of this helps

[MnDude45]

Targeting to get the first course sitting on top of floor. A couple of questions to verify the FB plans:

1) 1st course on the floor can be cut to fit, no mortar below or between
2) for the 2nd course and above, the bottom face should align and be placed directly on the course below (no mortar gap). Sides and back supported by mortar to keep the correct angle
3) if using a Chipster style jig with the dome spreadsheet dimensions for cuts, do I need to angle my first cut of start with the 2nd. I believe the spreadsheet assumes the 1st course is part of my floor.

looking for some confirmations before diving in.

As always, feel like I’m over thinking some things and overlooking important things.

Thanks,

[david s]

If any leveller is required it works better if it's applied dry.

[MnDude45]

I forged ahead today and blew past the point of no return. Winter is coming and I needed to either go or stop until spring.

Laying the insulation went well. If I would to do it again, I would follow Mongo’s advice and forgo the fireclay paste. What a fiasco. I had two restarts, I finally realized the FB instructions did not work for me. I started with a “sticky mortar” consistency but as I laid it down, it would set before I could get two bricks down. For the second half, it worked ok but struggled to keep level and ended with a couple gaps that were bigger than I hoped. Hopefully ash will settle and fill those after a while.

I kept the vent plan at 9” but do have a couple inches that I could extend, if needed. JR - Thanks for the pics. If I can ask, how wide was your vent opening in the outer arch?

It was a full day today and will need to push forward over the next three days in hopes of getting the dome complete, cured and enclosed before the snow flies.

[mongota]

mongota - Thanks for the feedback on both points. On the fireclay paste, I realized today when I was laying out the floor that not all firebricks are created equal. Some are slightly thicker/thinner and I think the base layer will help ensure an even floor. Did you have any issues with those?

C

I culled my pallet of bricks to find the ones most uniform in size and set those aside for the oven and landing floor. I'd take five or so bricks at a time, stack them like a deck of cards, and flip them all at once from one edge to another on a flat surface so the irregularly-sized ones would stand out. I set the odd sized ones aside. Then I'd compare for thickness. Once I had a sufficient number of uniformly-sized bricks I laid them out on my oven floor template in my desired herringbone pattern.

Even after the initial cull, after laying them out I still had to swap a few more bricks out. Sometimes I could rotate one end-for-end, or I'd swap one brick in the pattern for another brick in the pattern to minimize lippage. Or toss an outlier back on the pallet and find one more appropriate. It really didn't take long to do.

Once I had a decently smooth floor, I numbered the bricks, took a photo for reference, cut the bricks to the floor pattern and set them on the insulation.

Even after you build, if you end up with a brick edge that interferes with your peel easily sliding across the floor, you can ease the edge with a light pass of an angle grinder. I haven't had to do that, but I have seen posts from others who have done that.
MnDude45

[JRPizza]

The extra depth will certainly help you make room for your adapter and provide area for feeding your chimney, but you will still need to plan for transitioning from a rectangular opening to a square surface for your adapter. I did this my transition by building back towards the oven slightly. I "think" the pictures might show what I am talking about. You can also see in the first pic how the vent gets thin at the top and the extra length of the vent gives more stability as it allows the upper bricks to get wider. I think this gives more mortar adhesion area and more support for the weight of the chimney above it. You can also see how using the L shaped bricks back over the oven arch might add to that stability.

[MnDude45]

mongota - Thanks for the feedback on both points. On the fireclay paste, I realized today when I was laying out the floor that not all firebricks are created equal. Some are slightly thicker/thinner and I think the base layer will help ensure an even floor. Did you have any issues with those?

Regarding the arch dilemma, your mock up of my photo was very helpful. You are seeing the same thing as I am. I am planning a 6” ID pipe with a 10” plate. I think I’m going to extend out the landing tunnel but I’m going to trim the tunnel brick for 4.5” to 3.5” to keep it flush with inner arch. Rather than cut the notch for the thermal break, I”ll cut back the outer arch break and fill with fiber cord and hi-temp caulk. This almost the same as your suggestion for the floor but inverted for the arch ceiling.

Thanks again, I appreciate the ideas and thought process

C

[mongota]

I am laying out the transition from inner dome arch to the outer vent arch. I have planned a 1in offset between the two with a 1/2in notch as a thermal break. In looking at the pic, the flange that will create the overlap of the outer arch over the inner arch will only be 1/2in which just feels like not enough. I think i either need to increase the offset of the outer arch to 1.5 or 2 inches or lengthen the vent arch from 9in (1 std brick) to ~12in in order to support the chimney space. The cardboard on top represents the 10in needed to support the chimney anchor plate.

If i need to increase the offset of the outer arch, i will need to widen my planned floor footprint.

Any thoughts from yodas out there?

I'll offer an answer, but those that know better an certainly chime in with their ideas.

One issue I see with a 1/2" reveal at the dome arch is clearance issues if you want to use a flanged insulated door in the dome arch. The 1/2" clearance will be somewhat tight when sliding the flanged door in and out of the landing tunnel. I used a 1-1/2" reveal on my dome arch. I think upping yours to at least 1" would help down the road.

With your landing tunnel being only one brick deep, my first question is what is the inside diameter of your chimney pipe? It's a 36" oven, are you using a 6" ID pipe? A 9" tunnel brick less 1/2" cutout to cover the dome arch leaves 8-1/2". Less 6" leaves 2-1/2", or 1-1/4" of landing arch thickness in front of and behind the flue opening. That's rather insufficient. Simply my opinion. You can do it, but it's rather delicate. If you can I'd recommend increasing the depth of your tunnel. Most common is 1-1/2 bricks, or 13-1/2". You don't have to go there, you can do less. But the extra depth in the landing tunnel will provide better support to your chimney anchor plate.

If for example you increased your landing tunnel to 1-1/2 bricks, or about 13-1/2"? If you up your dome arch overlap to 1" and subtract your 6" inside pipe diameter, that leaves you with 6-1/2", or 3-1/4" thick landing arch bricks in front of and behind your flue. You can reduce that a bit should you chose.

I marked up your photo to try to convey my text...

Red arrow, increase the reveal to 1".

The buff colored is sort of showing a slightly less than 1-1/2 brick deep landing tunnel. It does not have to be that deep. I'm just trying to convey that a deeper tunnel may help with the chimney anchor plate, as well as with helping to prevent smoke from flowing out the front of the oven when you start your fires.

The blue lines show the flue, flared at the bottom with a 6" opening at the top for your 6" ID chimney pipe.

I hope this helps more than confuses.

Best, Mongo

[mongota]

The Forno Bravo plans call for a layer of fireclay paste on FB and under floor. If the hearth and therefore the insulation is level, is this step necessary??

Thoughts??

My answer is 'no'. If everything is flat and no additional support is needed, I'd say you could bypass the bedding layer. FWIW, I did not bed my insulation, it was simply dry set.

[MnDude45]

I am laying out the transition from inner dome arch to the outer vent arch. I have planned a 1in offset between the two with a 1/2in notch as a thermal break. In looking at the pic, the flange that will create the overlap of the outer arch over the inner arch will only be 1/2in which just feels like not enough. I think i either need to increase the offset of the outer arch to 1.5 or 2 inches or lengthen the vent arch from 9in (1 std brick) to ~12in in order to support the chimney space. The cardboard on top represents the 10in needed to support the chimney anchor plate.

If i need to increase the offset of the outer arch, i will need to widen my planned floor footprint.

Any thoughts from yodas out there?

[MnDude45]

Another question regarding the high temp mortar…the FB recipe calls for:

•1 part Portland cement
•3 parts sand
•1 part lime
•1 part fireclay

Regarding the sand, is this meant to be regular play sand or a silica sand? For the lime, this is meant to be a hydrated lime I believe.

Also, other than cost, what are pros/cons of using a store bought high temp mortar such as the Akona medium duty refractory dry mix or a premix such as Meeco’s red devil fireplace fire brick mortar in a bucket?

thanks,

[MnDude45]

I spent the weekend reviewing my build plans, laying out my arch templates, screening the weep holes and cutting/laying tile on hearth as FB underlayment. I have a question about the placement of the oven floor on the FB. The Forno Bravo plans call for a layer of fireclay paste on FB and under floor. If the hearth and therefore the insulation is level, is this step necessary??

Thoughts??

[MnDude45]

mongota - I like that option for the floor thermal break. Thanks!

[mongota]

Is a 1/2inch an appropriate gap between the dome floor and entry way? I’ve seen some builds use a stainless steel channel on top of fiber board used on the floor. Thoughts?

Another way is to cut back the edge of the brick where the oven floor meets the landing floor. It may help reduce conductive heat loss between the two. I don't think it's much of a true performance benefit unless you're really fighting to save every bit of heat loss you can. The lower part of the cutback could be filled with insulation. Let ash fill the top of the gap to seal it off.

[david s]

Thermal expansion will take up 5 mm at most for the temps we fire to. Using a highly conductive material in a gap designed to prevent conductive heat transfer is counter intuitive IMO. The gap’s primary function is to act as an expansion joint to prevent stresses on areas that are cooler. It will reduce conductive heat somewhat, but a small gap will do little to reduce heat by radiation.