42" build in McPherson KS

[slschoming]

Seth, If you have not built your inner arch form yet now would be a good time. You can set the form in the location you have chosen for your arch, set a brick on the top of the form, and use your IT to make sure the dome and arch will mate properly.

I have not built it yet. I am thinking it will be 3 bricks of straight wall with a partial arch on top.

The inner arch alignment looks good now. I suggest that you make your IT adjustable and the key is that the centerline of the pivot point at the floor hits the centerline of the brick, ie if your brick is 2.5" thick then the centerline of the IT from the pivot point will should hit the brick at the 1.25" mark. There was a recent non-weld wood IT that was done recently that was adjustable. You do not say how high your arch is but it should be abt 63-65% of the dome height, width is not as critical. If you are doing a tapered inner arch (recommended), then you will be using full length bricks on arch not halves, the full length give you material to work with. The top dead center of the arch will be the longest brick, tapered inner arch make the dome to arch transition much easier.

I think my center / pivot point is at floor level, and I did make sure the bracket is centering my bricks to the dowel. I grabbed some stuff at the hardware store on the way home yesterday and will work on making an adjustable version.

My opening is going to be 13.5" and my dome height is 21" (64.3%). I would like a little wider opening like I had originally planned (25-26"), but I saw that apagios warned about losing too much heat with a wide opening. He uses loose cut fire bricks on the sides of his inner arch to slow down the outflow of heat when doing pizza, which I think is a great solution, I just think I would be constantly knocking those over with my peel and having to get gloves on to put them back up. So I am currently planning to narrow it down to about 22 inches wide.

Apagios, have you had any luck with a turkey?

[JRPizza]

[JRPizza]

Seth, If you have not built your inner arch form yet now would be a good time. You can set the form in the location you have chosen for your arch, set a brick on the top of the form, and use your IT to make sure the dome and arch will mate properly.

[UtahBeehiver]

The inner arch alignment looks good now. I suggest that you make your IT adjustable and the key is that the centerline of the pivot point at the floor hits the centerline of the brick, ie if your brick is 2.5" thick then the centerline of the IT from the pivot point will should hit the brick at the 1.25" mark. There was a recent non-weld wood IT that was done recently that was adjustable. You do not say how high your arch is but it should be abt 63-65% of the dome height, width is not as critical. If you are doing a tapered inner arch (recommended), then you will be using full length bricks on arch not halves, the full length give you material to work with. The top dead center of the arch will be the longest brick, tapered inner arch make the dome to arch transition much easier.

[slschoming]

It looks like I will have 13.75 inches for my vent/landing area.

[slschoming]

In the photo below I have ROUGHLY marked out my new plan. The blue arc is roughly the curve of the IT and the red lines are to show how much landing width I will be reducing to get down to about 22 inches wide. Where the red and blue intersect is where the inside of my inner arch should begin and I have drawn the portion of the landing that will be covered by the inner arch in green. This leaves me more area for a proper vent than I was thinking yesterday.

The diagonal of a 4.5 inch square (marked in yellow) is 6.364 inches and I have another 4 inches between what I have laid out in this picture and the edge of my hearth. I am estimating about 14 - 15 inches left between the outer edge of my inner arch and the edge of my hearth.

UtahBeehiver Does this seem like I have a better understanding than I did yesterday? Does anything stand out to you as incorrect?

Thanks!

[slschoming]

I have a short landing too...I was following another builder on this site who did this as well and his point was that it's easier to work the oven with a shorter landing so I think you'll be all good IMO...keep up the good work! Zoo

Hey zoolander , check out fxpose's cast vent:

https://community.fornobravo.com/for.../page5?t=12677

I might explore something like that for my short landing.

Happy building!

[slschoming]

The arc of the IT should intersect the inside of the inner arch brick at the edge of the arch form and dome wall or it will be harder to mate the inner arch and dome walls together and keep circular.

UtahBeehiver Gotcha, thanks for catching that.. I was planning the opposite.. to have the IT arc intersect the OUTside of my inner arch... I will do some more measuring and try to get that all worked out as I decrease the width of my opening / landing.

I hope I left myself enough room at the front edge of my hearth for my vent, etc.. it looks like I will only have about 10.5 inches between the outside of my inner arch and the edge of the hearth

Thanks!

[UtahBeehiver]

The thermal break is a scrap piece of SS rectangular thin wall tubing. Channel will work as well. I chose SS due to the lower K value vs carbon steel or aluminum. It is stuffed with leftover ceramic blanket. The arc of the IT should intersect the inside of the inner arch brick at the edge of the arch form and dome wall or it will be harder to mate the inner arch and dome walls together and keep circular.

[slschoming]

I am going to take SableSprings advice and add a thermal gap between my floor and landing. On the landing side of the thermal break I will have straight bricks instead of the herringbone pattern. Should the bricks on the landing floor still be fire bricks or does it matter?

UtahBeehiver I was looking through your photo album (again) and came across the photo attached below... is this your thermal/expansion break? What material did you use there?

The other photo I am attaching here shows where I plan to cut my floor bricks to add the gap. The way things will fall, I think i will be an inch or so behind the front of my inner arch, but I think any door that I would design would cover the gap well enough to isolate the two sides from each other so with the door on I will not be heating the landing with ambient air, and on the other side of the coin I won't have any of my heated floor bricks outside the door acting as a heat sink. Does that seem like an ok location for the gap? Am I overthinking this again?

After doing some more reading on the forum I think that I've decided that my planned opening is too wide (about 26") so I will be bringing that down to about 22" so I don't lose too much heat.

Thanks in advance!

[slschoming]

SableSprings Thanks for your reply! I know I probably overthink the details of this oven, but what else am I supposed to do during the work week between build days?

I've attached a photo of how I was planning to interface my herringbone fire bricks to my straight plain bricks. I think it's similar to what you are saying (my bricks are a different orientation than the straight bricks in your photo), but I may have to trim a little so it's not as tight and so I can fit some fireplace gasket or rope and still be flush with my edge. Does that seem reasonable or do you think I need to go deeper into the landing with my regular bricks?

[SableSprings]

As David S noted above (post #72), CalSil (board and batting) is extremely hydroscopic (loves to soak up and retain water). Again, as David S noted, water barriers like RedGard and FoamGlas are good at keeping water from contacting (and being absorbed by) CalSil. The other side of the coin for painted/applied membranes...and it's really an important one...is that the membrane will also prevent moisture from escaping. That's not a problem with the FoamGlas. In both cases you want to provide an escape route for any water/moisture that finds its way underneath your oven. So in both cases, the weep holes provide exit paths for the unwanted liquid(s).

Zoo - since you are putting in dry CalSil board, don't have weep holes, and have provided a water barrier on the bottom and sides of the oven insulation base, your primary focus is to keep water from entering through dome/sides/perimeter cracks in the outside render. The best option is to build an external cover/structure for your oven. Lots of pretty straight forward examples in the forum, bottom line is that you are trying to create a situation in which water is unlikely to get on or even near your oven. Installing a small, dome vent also helps allow moisture to escape from the upper insulation after periods of sitting in high humidity climates/situations.

I also favor the larger enclosure concept for WFO projects simply because it extends the time the oven can be used, extends the time the person working the oven stays dry in inclement weather, creates a dry place/space for food prep/serving next to the oven, and gives guests a shelter from the storm (until the adult beverages kick in and they don't really care anymore ). Obviously in addition, my personal bias is to screen a larger enclosure to exclude hungry yellow jackets, mosquitoes, and annoying flies while using the oven and entertaining.

Seth - There is some controversy about the value of creating an insulation gap between the oven and the outer gallery/landing. I'm with the school that believes the temperature retention advantage using that technique is minimal...having an insulated oven door that seals tightly against the reveal is more important (IMHO). That said, providing a small gap between the heated/working portion of a WFO and the cooler chimney/flue gallery is more important to provide an expansion gap than to retain heat. Not too many of us are looking at really extending the cooking/baking time beyond a couple of days on a single firing (again...IMHO)...but there is something magical about having the oven stay hot for longer periods of time.

As to keeping the herringbone pattern...notice that you will have some small pieces at the front edge of your landing. It would be better to cut back in the landing (one brick length from the edge) and place a row of bricks across the front. That way you could put in a small gap (filled with fireplace gasket/fiber rope) for your expansion/insulation space and then lay & set the full bricks out for the main wear and tear area of the landing. Just a thought, but I think those small cut pieces of the herringbone pattern front will become problem in the future. I've put in a picture of my interface between the herringbone and straight bricks...you'd probably go further out in your landing area for the cut...but the picture should help you visualize this.

I do not have weep holes beneath my oven, I do not have any insulation/expansion gaps, I did not put in a moisture barrier beneath my oven, and I wish I would have put a thicker layer of perlcrete under the cooking floor. Based on primarily the innovations by members of this forum during my 10 years as a member, I would change many things about my oven if I could do it over...BUT...and this is a BIG but...I have put almost 3.5 tons of dough through my oven since it was completed in the fall of 2009 (that dough amount includes nearly 4,000 items like pizza, buns, breadsticks, etc. and almost 5,500 loaves of bread). I have no complaints about my oven build (and neither do any of my friends or neighbors).

Relax...some builds are more "technically correct" than others, some are "prettier" than others, and the ovens built in Pompeii over 2,000 years ago (some still standing!) would work just fine today...almost any materials you use for your build will be better than what those poor Romans had... Ultimately, with proper maintenance & care, your oven (cast or brick) will work great and allow you to produce many a fine meal for years to come!

[slschoming]

I laid out my floor and re-found my center point, which was inconveniently located right where three bricks intersect. I was hoping I'd only have to remove 1 brick for my IT pivot point, but instead I had to remove three and cut out a stranger shaped piece of plywood...

I have not mortared anything yet, but I have dry stacked 2 full courses plus a few bricks. I am already starting to see a minor inverted V on course 3...

I have read that some people put cardboard between the floor and the dome wall before mortaring, is that a common practice? I have not seen any photos of this step and am not sure what thickness of cardboard to use.

SableSprings you mentioned that it is best practice to put "an insulated gap around the oven opening and front arch set(s)." I just want to make sure I am understanding correctly... Should I be cutting a line where the floor (circle) meets the landing (rectangle)? What is used to insulate the gap between the floor and the landing? How thick should the gap be? I really like the herringbone continuing from floor to landing but if it is going to cause issues then I am willing to modify..

I am getting excited, it is actually starting to look like something! Thanks to all who have helped me so far, I love this community of support!

[david s]

I was wondering if I could get your input on water mitigation....I will be enclosing my build but I will be using glued pavers for the walls which will allow some moisture to get in....I put the 2" of fiber board on top of sheets of 3/8th Durock board that I coated with Redguard vapor barrier....I'm also planning on using Redguard around the edge of the insulation that sits on top of the Durock board and then maybe do some flashing around the perimeter of the paver block from the inside along with caulking?? I'm honestly pretty paranoid about water entering into the oven so any thoughts or help would be much appreciated!! Thanks, Zoo

Fire wil push out the water, but if there’s plenty of it then it can take more time than you’d think. Your oven will still work , but as water conducts heat well, wet or moist insulation doesn’t insulate so well. In my build (igloo) wet insulation is easily indicated by holding a hand to the outside of the dome after the oven has been fired for around an hour. If the insulation is not dry it can feel hot to the touch. If dry it feels either stone cold or slightly warm. This test of course would vary from oven to oven and many factors determine rate of heat penetration. Remember that any sealing you do to prevent water entry also prevents its escape. This is why drain holes in the supporting slab greatly assist in water removal. I’m also a believer in having an escape in the upper area of the dome (if building an igloo) which acts like a hole in a saucepan lid, both for pressure release and moisture escape.
We live in the tropics and really high humidity even without rain for a week or so will be enough to reduce the ovens insulation capacity. If you were to use the oven daily, then of course moisture would never get a chance to make a problem, but as we usually use our ovens occasionally we’re often pushing moisture out. So providing pathways out is just as important an preventing its entry.
i’ve been doing some tests on absorbency and drying of various insulation materials and my cal sil board absorbs 144% of its mass in a 5 sec immersion and a whopping 318% in 24 hr immersion in water. Using foamglass on the bottom is a good idea as it does not absorb water.

[slschoming]

zoolander
I was looking at your build the other day and was envious of your speed! I have been going at this since September, getting maybe 1-2 good build days in per month. Keep up the good work!

I was wondering if I could get your input on water mitigation....I will be enclosing my build but I will be using glued pavers for the walls which will allow some moisture to get in....I put the 2" of fiber board on top of sheets of 3/8th Durock board that I coated with Redguard vapor barrier....I'm also planning on using Redguard around the edge of the insulation that sits on top of the Durock board and then maybe do some flashing around the perimeter of the paver block from the inside along with caulking?? I'm honestly pretty paranoid about water entering into the oven so any thoughts or help would be much appreciated!! Thanks, Zoo

I am also paranoid about water. Unfortunately, I have more questions than answers myself. Maybe SableSprings or UtahBeehiver or david s could answer for you?