Pizza Bob's 42" Build

[pizza_bob]

Re: Pizza Bob's 42" Build

The oven will be getting stone veneered this coming week. I picked out the stone but still haven't decided on a stone for the front entrance shelf. What have others used? I'm worried about staining and how hot it will get. I fired my oven for six hours this past Sunday at the vent area floor bricks got up to around 250 degrees so the heat shouldn't be too much of a concern.

Here are some pictures from this past weekend. The eggplant pizza was really good!

~Bob

[pizza_bob]

Re: Pizza Bob's 42" Build

George,
I thought so too. This material is thier 5/8" DensGlass which they call FireGuard! It's used on commercial building exteriors all over the country and temps in Arizona and Florida push this material over 125 degrees! I'm not as concerned after the high heat test I did. I am having the oven veneered with thin stone this week which I believe should help the situation. Georgia Pacific also gurantees this material to be exposed to rain/moisture for up to 12 months prior to applying a veneer or stucco. I thought this was the best material for me to use until their engineers told me to keep it under 125 degrees...Oh well. It's not coming off now...

[fxpose]

Re: Pizza Bob's 42" Build

The enclosure walls are up and ready to be veneered. I ended-up using a material called DensGlass. I kinda' have had second thoughts about using it after I called Georgia Pacific (the manufacturer).
I asked them how this material behaves with heat and they recommended keeping temperatures below 125 degrees Fahrenheit.

125F seems awfully low for a building material. I would think it can tolerate higher temps.

[pizza_bob]

Re: Pizza Bob's 42" Build

Here are photos of the raging fire and pizzas. If you look closely at the first fire picture you can see flames going up the flue!
Also look closely at the picture with the fire pushed to one side and you'll notice the small chip in one of the bricks and how clean the mop gets the bricks!
I also notice I don't get a BIG bed of coals! The picture below is the result of burning a lot of wood for 6 hours! It's all oak but I thought I would get more coals.
Also...It's amazing how the ENTIRE dome gets cleared of black soot and turns back to the brick color at 900 degrees! The black soot at the vent area (inner arch) started to turn like a white color that I never saw! The dome went from black to brick color but the inner arch went from black to white powdery looking color. You can just notice the white it in the third photo below...

~Bob

[pizza_bob]

Re: Pizza Bob's 42" Build

I haven't posted for awhile and just wanted to get my thread up to date...

The enclosure walls are up and ready to be veneered. I ended-up using a material called DensGlass. I kinda' have had second thoughts about using it after I called Georgia Pacific (the manufacturer).

I asked them how this material behaves with heat and they recommended keeping temperatures below 125 degrees Fahrenheit. So I did a test firing Friday. I brought the oven up to 950 degrees and held it there for 5-6 hours. I wasn't concerned about the walls around the dome getting hot but more worried about the front wall above the oven entryway. The temperature never exceeed 95 degrees there! The DensGlass doesn't contact the front arch and I put some insulation between the arch bricks and DensGlass so I think that really helped. The vertical walls never changed temperature and the roof (angles and flat) never changed temperature. The problem with the DensGlass and high temperatures is that the sheets are made of gypsum. Gypsum is 20% water and if dried out they can start to deteriorate. I really had an AWESOME fire going in the oven! I had flames shooting up the flue - so cool! The reason why my walls didn't change temperature is because I have 3" - 4" of ceramic blanket and then we dumped in 80 cubic feet of loose grade A4 (larger size) vermiculite. It ended-up giving at least 4" of vermiculite at the base of the dome and about 6" on top. I don't have a door per say other than a thin piece of particle board which leaks but I used it to cover the opening only at night and left ot off during the day. I checked the oven temperature today, 48 hours after removing coals, and the temperature of the dome was 210 and the floor was 185.
I did also end-up cooking some pizzas. The first one went in when the floor was 800 degrees. It cooked/charred in about 90 seconds. I bought a mop to clean the hearth which works really well! It brought the temperature down to 750 degrees and a mozzarella/onion pizza came out great! I did a mozzarella/pepperoni after that which also came out great.

I'm really happy with the oven so far except for one thing...The cooking floor bricks seem to have shifted! I left a 1/8" expansion gap around the perimeter of the oven when I laid the soldier course. I think the bricks might have shifted because of that and now there is a spot in the middle of the oven that has a gap that is just less less than 1/8" wide. I also noticed a small chip in one of the bricks. Not sure if that was from the pizza peel or a large log that fell off the fire during heat-up. You can make it out in one of the photos in my next posting below. Is it possible to lay large 12" x 12" ceramic tiles over this floor? Has anyone ever tried that? I thought I might be able to throw down a very thin layer of sand/fireclay and then put these larger tiles on top of the exisitng floor. I don't mind the longer heat-up time and I can get the dome height down to 18.5".

~Bob

[eatingmorefood]

Re: Pizza Bob's 42" Build

Pizza Bob,
Hello ! Your oven looks amazing.
I'm busy cooking and eating, all the time, but finally I am Builiding my first oven, likely a 36 in. ID Pompeii style! Slad in ground, my blocks are up getting ready to frame and pour hearth slab.
Wondering how thick my support slab should be ? Hearth is 48 x 48 in. and plan to use 10 pieces of 1/2 rebar in slab. Then a second slab of vermiculite - concrete mixture on top of the slab. Is this correct so far ?
Call me crazy, but I plan to recycle a large pile of pizza oven stones into this oven.
thank you !
Chef

[pizza_bob]

Re: Pizza Bob's 42" Build

Thanks Dino! I look forward to those wine breaks!
I'm not too worried about how well the oven holds the heat. I went out today, which is 4 days since firing it for a few hours and measured the temperature with the laser gun. The dome was still at 105 degrees and the floor was 100!?! It's been in the 40's and 50's here at night and this thing is still warm! Unbelieveable.
We put the metal studded frame up today. A friend built the walls and the hipped roof in his workshop and then came here to assemble it all. He did a great job! Everything lined-up perfectly. It's looks a little taller than it looked on my CAD models and drawings but I think once the stone veneer and decorative arch are in place this will not appear to be so tall. We are also having retaining walls flanking both sides of the oven which will be started next week. These walls should make the appearance not as tall too. Other than that I think it looks great. The 18 gauge steel is heavy-duty and this will be used as our torando shelter!

~Bob

[Dino_Pizza]

Re: Pizza Bob's 42" Build

The pizza looks awesome Bob. Your oven is retaining heat just fine.

I find that I re-charge my floor for a few minutes (rake the coals back over the middle for about 5-10 minutes, maybe add a smallish log) after 5 or 6 pizza's. I don't think I can go 12 unless the dome and side flames happen to reduce the perfect amount commensurate to the floor cool-off to compliment cooking the pizza (with the right toppings for that heat temp). Then it's just pure luck but I guess it could happen.

Anyway, that's my experience and I'm sticking to it.

Your ceramic blanket looks great! Nicely fastened to the dome too. You're going have a great time making pizza's and finding out how long you can heat load your oven floor. Besides, re-charging the floor is a perfect time to refill your glass of wine and find out if anyone has left the chef any pizza .

-Dino

[pizza_bob]

Re: Pizza Bob's 42" Build

Tman1,
Thanks. Once the oven hit 900 degrees I kept it at that temp for about an hour. The bottom of the pizza seems to be cooked more than the top. If anything I want to lower my dome and I'm at 19 1/2" tall.

~Bob

[Tman1]

Re: Pizza Bob's 42" Build

Ahhhh, the first pizza! How gratifying! How long did you heat it up prior to cooking the pizza? I think it best to get the floor even hotter than that (closer to 700-750). I did some pizza last weekend and my floor wasn't hot enough.. affected the taste negatively in my opinion.

[pizza_bob]

Re: Pizza Bob's 42" Build

Here are some pictures of my first pizza. The dome was completely black but quickly cleaned up when temps hit 900 degreess. It's nice to see the dome back to its original color after all these curing fires. The pizza was just mozzarella, sauce and fresh basil from the garden. I was surprised I didn't burn the bottom. The pizza cooked in 2.5 minutes with the dome at 750 degrees Fahrenheit and the floor at 650. Immediatley after removing the pizza I measured the floor to be 630. I hope I don't regret not having more thermal mass and insulation under the floor. The insulation under the floor really seems to work well because there really isn't much temperature rise hours after firing in the wood storage area ceiling. Is one layer of bricks really enough thermal mass to get say 12 pizzas cooked without having to recharge the floor? I have 2.250" inches of vermicrete (mixed 5:1 ratio) sitting on top of 2.00 inches of FoamGlas. The FomaGlas really is a great insulator but I wonder if I should have gone thicker with that and/or the vermicrete. I'll find out this weekend when I try to make more than two pizzas...

~Bob

[pizza_bob]

Re: Pizza Bob's 42" Build

I got my insulation on yesterday. Three blankets of Unifrax DuraBlanket. All of the dome is covered with at least three inches of blanket and some overlapping areas have four inches. I used boiler strapping and TapCon screws to hold the insulation in place until my enclosure is complete. Once the enclosure walls are up I'll fill the rest of the area with loose vermiculite. How many times have we heard the phrase "You can not over insulate!"? Well I have researched this so much that I finally stumbled across information that says "too much insulation starts to work against you"! It seemed so counter-intuitive at first but once you look at the equations for heat transfer it actually makes sense! When insulating circular or spherical objects the surface area increases which increases convective heat transfer (heat loss). By adding three inches of insulation to a 42" oven the surface area increases approximately 23%. This increase in surface area increases the heat loss. The equation for convective heat transfer is:
q = k A dT
where
q = heat transferred per unit time
A = heat transfer area of the surface
k = convective heat transfer coefficient of the process
dT = temperature difference between the dome and outside air

You can se that as the area increases so does the heat loss. The thickness of the insulation does not play a role in convective heat transfer.

But the thickness of insulation does minimize conductive heat transfer. The equation for conductive heat transfer is:
q = k A dT / s
where
A = heat transfer area
k = thermal conductivity of the material
dT = temperature difference across the material
s = material thickness

From this equation you can see that insulation thickness does minimize heat loss because the thickness (s) is the denominator. So as the thickness increases the heat loss decreases but....Area is also part of this equation which works against you in conduction too.
It gets to be a balancing act between surface area vs. thickness that results in a point of diminishing returns. I'm sure I didn't do the best job explaining this but Google "critical thickness of insulation" if you're interested for better explanation. Here is a link that might help too:
Critical Radius of Insulation

This caught my interest and I thought it might be worth sharing. So sorry for be long winded.

I did insulate my dome and it seems to work well. I had the fire at 900 degrees Fahrenheit for a couple hours, cooked my first pizza in 2.5 minutes and then pulled the coals out. I then left the oven open with no door for four hours before i had to go to sleep. So I put a piece of particle board that I had used for my inner arch across the doorway overnight. It doesn't fit well so it leaks all around and it's really thin. The temps dropped down to mid 40's last night and my oven dome was still 375 degrees and the floor was 350 at noon the next day. I thought that was pretty good for 4 hours of no door and twelve hours with a particle board door. The concrete under the hearth (ceiling of the wood storage area) was 73 degrees at noon and outdoor temperatures were around 60 degrees.

Anyway...Here are some pics of the insulation process. I'll follow this up with pizza pictures.

~Bob

[pizza_bob]

Re: Pizza Bob's 42" Build

Thanks again Darren!

I contacted the manufacturer of the steel studs I'll be purchasing/using. I explained my project and they asked what is the weight of the stone veneer. I was able to find the data sheet for the Virginia Ledgestone veneer that I'll be using. The weight is 11.6 lbs per square foot. I calculated the square feet of my enclosure and the stone weight alone, excluding the cement board and scratch coat, is approximately 2200 lbs!! I never imagined the veneer stone would be that much! So their engineering department reviewed the drawings I sent them and they ran some calculations for me and determined I should use the 18 gauge studs. These studs are .0451" thick. The steel studs are from Marino\WARE - metal framing systems, lightweight steel framing for commercial and residential buildings.. Their technical services group was great! They replied immediately with an answer after I sent them my drawings. I attached a JPG for my stone veneer and the structural catalog from Marino-Ware can be found at this link:

http://www.marinoware.com/Documents/...%20Catalog.pdf

They recommended I use 358SW18 stud and space them 16? on center. They also recommended the screws that I should use: (4)#10-16 screws.

This thing should be framed by next week. I'm having someone else do this for me...

~Bob

[dbhansen]

Re: Pizza Bob's 42" Build

I think I went with the heavier gauge (probably a good idea for a stone veneer). Mine were aluminum.

[pizza_bob]

Re: Pizza Bob's 42" Build

Thanks Darren,

What gauge metal did you use for your studs? Was it 25 or 20? I need to decide today on which to go with. I'll be hanging cement board with a stone veneer so I'm leaning towards the 20 gauge. These studs are aluminum?

~Bob