42" build in McPherson KS

[slschoming]

I just ordered enough CaSi and Foamglas to do a 2" layer of each. Should arrive to the warehouse next week and then I will have to find the time to drive 3 hours round trip to pick it up...

For those with weepholes and Foamglas.. Is laying a sheet of mosaic tiles underneath overkill now that I am using foamglas as my bottom layer, or is it still advised?

My kids are starting to question whether I am going to really get this thing done:

"Dad, when are you going to start working on the pizza oven again?"

"What if you mess up and can't fix it?"

[UtahBeehiver]

Are you enclosing the oven or not? Open ovens are prone to having water come in from the hearth. A weep hole would be cheap insurance in case any water works its way in. Even though the FoamGlas will not absorb water it would be advantageous to have any water that migrates in able to egress out.

[slschoming]

UtahBeehiver I have 2 weep holes located along the perimeter of where the insulation will sit. I was previously planning to put my CaSi board on some sheets of mosaic tiles to keep it up off the (potential) water. Now that I'm planning to put a layer of foamglas under the CaSi I'm curious if I still need the mosaic tile.

The current plan is to have an exposed dome that I will eventually finish with remnant brick like cobblerdave 's oven.

[SableSprings]

Seth, as Russell noted, even with the non-absorbing Foamglas underneath your CaSi board, having the mosaic tile sheets allows any water that seeps in underneath the oven, a clear path drain out the weep holes. That's why setting the sheets upside down (with the webbing up) works...you get little channels for any water to flow out to the weep holes. Also gives you little air channels to help dry out any moisture wicking up from the concrete. As with the weep holes, in your case with the Foamglas under the CaSi it's just cheap, extra insurance...just make sure you set the mosaic tiles so weep holes are not covered. Also don't forget to cover the lower (underneath) weep hole openings with some pieces of insect screen (metal if possible). Silicone seal will hold little squares of screen nicely and keep any critters from looking for a new home in your insulation layers. I'm not fond of the plastic screen materials, seems like the bugs often just chew through it too easily.

Good luck and glad to hear you're back working on the oven!

[slschoming]

Earlier this week I picked up my insulation for under the floor and about 140 firebricks (enough to get started). Next week I will start cutting the insulation and floor bricks. I have changed plans since I started.... I will be building a 42" internal diameter oven so my insulation footprint will be a circle with a 51" diameter connected to a rectangle for under the landing. However, I have a few more questions before I get started.

Insulation Question
I was curious if there is any benefit in having the floor insulation extend another 2 inches beyond the outer layer of firebrick so that the bottom of the 2" insulation blanket is resting on CaSi board. Has anyone done this? Or is it better to overlap the other way, having the blanket extend below the bottom firebrick enough that there is no heat sink?

Opening Question
I think I read somewhere that a good opening for a 42" is around 20" - 22"? Is this a decision that should be made based on science, or is it mostly personal preference?

Landing Question
Since I started planning a 36" oven my hearth is probably a little smaller than the average 42" oven hearth. I am going to be extending my landing all the way to the front edge of the hearth and will be utilizing every last inch of space that I have.. That being said, how much of the landing should be above insulation? I am currently planning to run my insulation 4 inches short of the front edge of the hearth so that I can put a full brick down (stretcher orientation) between the edge of the hearth and the insulation. I am open to suggestions.

Thanks!

[SableSprings]

Seth, here's my take on your questions:

Insulation: The goal of your insulation is to totally isolate the heated oven bricks from the stand and any other outside contact. There would be no problem having the CaSi board extend a bit further to "connect" with the upper dome blanket. Just be very aware of providing a moisture barrier and moisture escape route for all insulation (top and bottom). Water seeping in along the perimeter of the dome's outside base is one of the top problems for a WFO that is not in a permanent, roofed enclosure

Opening: The opening width is not as important as the ratio of opening height to inner dome height (remember the magic 63%). The biggest decisions for me were 1) making sure I could fit a full sheet pan easily into the oven and 2) what worked out simply by the brick dimensions I was using to do my build

Landing: Best practices indicates putting an insulated gap around the oven opening and front arch set(s). The base insulation would not need to extend further than this gap. For a lot of people it is just more convenient to extend the insulation out to make the landing bricks the same level as the cooking floor. If your landing extends out a brick or two from the opening, then your plan sounds great. The bricks outside the oven on the landing can get plenty warm, but I seriously doubt there will be any issues for you (and it will look great with that front brick edging )

Hope that helps.

[slschoming]

Thanks Mike! I feel better about things now. I am going to be off the grid on a backpacking trip in Northern Cali for a week (leaving today), but I think I have all the info I need to get started when I get back!

Thanks again!

[slschoming]

Finally got to work a little more on the oven today. I put some ceramic tile down under my two layers of insulation. Next step, the floor.

[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?

[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]

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!

[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]

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?

[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!

[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.