32" build in Calgary, AB - pompeii neapolitan

[IH123]

I today started curing the oven with electrical heater (without any dome insulation) to dry the bricks out before winter freezing as if there is lots of moisture in it and temperatures gets lower than 4c it could freeze and cause cracks. I tried today a heater at 750 watts setting , it has thermometer so I set it to shutoff when air temperature reaches about 43C. I plan tomorrow to increase that to about 60C (or whatever its allowed to by the heater as long as its <60C). I will run it all day long while I am at home and turn it off at night. no tarp or covers at night as its still not below freezing for next 14 days (forecast) so to let anything evaporate and not get trapped in a tarp at night.

[IH123]

I am left with 22 unused bricks from the 188. That's I used 166 bricks. however I wasted by wrong cuts few of them, I estimate less than 10. therefore the actual exact number of 9"x4.5"x2.625" bricks used was 156. for mortar, I used 3, yes, x3 50lbs +x1 25lbs of Thermobond 915 refractory mortar, which is 175 lbs total. I would estimate the waste in mortar was about 25lbs so total 150lbs are in the oven. the bricks produced >= 4 large pails of grog( each would have about >15 litres by volume or >60 litres total, which is equivalent to >=115kg, which is equivalent to >=35 full bricks, which is >22% waste. with one full brick weight is 3.3kg, the oven mass wold be about :
156x3.3kg(bricks)+68 kg cured mortar- brick cut grog waste of 22%x156x3.3kg=~470kg

I have halted warming up the oven as the weather cooled down during a storm and I will continue warming/drying after it finishes as temp will swing from +10c to +21c (during the day) which makes warming the oven with 750 watts more productive.

and now I am scrambling to design and build a heavy duty snow shelter for the oven as the dome is pure unprotected brick.

[IH123]

I today cut to shape and descaled the A36 carbon steel door(3/16" thick), I drilled for handles and thermometer . I will season it with 500,000BTU propane torch and grape seed oil to prevent rust. I will not paint as inside face wont work well with paint. I will use 1/4" stainless steel threaded rod with nuts to secure a wooden handle(two, one one each side) . yet to use flapping disc to smooth the surface and clean it with alcohol before applying the grape seed oil. pictures of assembly before smoothing and seasoning (pending):

[david s]

A heavy carbon steel panel door is very conductive and has a lot of thermal mass, so although it is durable it is a less than ideal material, because especially if uninsulated it will draw valuable heat from the oven. See how it performs, but you may want to consider attaching an insulating panel to the inside face to improve performance.

[IH123]

A heavy carbon steel panel door is very conductive and has a lot of thermal mass, so although it is durable it is a less than ideal material, because especially if uninsulated it will draw valuable heat from the oven. See how it performs, but you may want to consider attaching an insulating panel to the inside face to improve performance.

you are right. I however plan to create a wood pan with same shape as the steel part, which have around 1" egde and use fibre glass gasket to hold the steel and wood tight together touching on gasket. will drill tiny holes in the wood container to vent. this will use air gap insulation between the steel and the outside wood. this will be made when creating the wood handles.

[IH123]

here is the design. the stainless steel threaded rod will penetrate across all layers and the wooden handles (not shown) will compress further the wood face to the steel face compressing the fiber glass gasket:

[Giovanni Rossi]

I've been delayed building v2.0 of my insulated wood insert. I get days of retained heat cooking with just my steel door, but I wanted to experiment to see how far I could extend that.

v1.0 was made using maple encased Foamglas. The lesson I learned was the need to respect the flameless spontaneous ignition temperature of hardwood (~450^oF). The inside face of the insert was destroyed after two uses.

With v2.0 I'll use my steel door until the oven temp drops below that. Even with that technique, the hardwood will char and be damaged over time. Your design will allow easy replacement of the wood panel once that happens.

[IH123]

I am actually thinking that if I use a thin steel sheet instead of wood , having it bent inside to form a seam of a pan all around, then fibre glass gasket between inner thicker 3/16 plate and outer thin steel pan would probably still provide very good insulation even with bolting (not welding). this is because the cross area remains to transfer heat by direct contact is very small (4x1/4" diameter circle area) . air inside is extremely low density so even if its spanning the entire volume , the heat transfer through air will be very small (think about it like if air is compressed into liquid, wont be even a drop from that volume of 10x17"). the decision of what material to use will be made based on simplicity and cost, as I feel not much difference of the material insulation value when its insulated with a gasket. At the end, the door it self is not pressure locked so no matter how far someone go on insulating the door, the heat will simply push the door open and run out.

[Giovanni Rossi]

I am actually thinking that if I use a thin steel sheet instead of wood.

Well, that's certainly a different animal. I was just providing a little color commentary on your posted design based on my experience.

I'm intrigued by the history of using wood doors before metal plate was available.

At the end, the door it self is not pressure locked so no matter how far someone go on insulating the door, the heat will simply push the door open and run out.

If you've looked at my build you may have noticed that I had good success using a bead of Permatex gasket on the steel door

[david s]

I am actually thinking that if I use a thin steel sheet instead of wood , having it bent inside to form a seam of a pan all around, then fibre glass gasket between inner thicker 3/16 plate and outer thin steel pan would probably still provide very good insulation even with bolting (not welding). this is because the cross area remains to transfer heat by direct contact is very small (4x1/4" diameter circle area) . air inside is extremely low density so even if its spanning the entire volume , the heat transfer through air will be very small (think about it like if air is compressed into liquid, wont be even a drop from that volume of 10x17"). the decision of what material to use will be made based on simplicity and cost, as I feel not much difference of the material insulation value when its insulated with a gasket. At the end, the door it self is not pressure locked so no matter how far someone go on insulating the door, the heat will simply push the door open and run out.

The thinner the steel the greater the propensity to warping from the heat and in this regard stainless is far more susceptible. Fixing an insulating panel to wood should be done with bolts rather than screws because the expansion and contraction of screws wil loosen them. Bolts should be as small in diameter and in number as possible to minimize conductive transfer ( I’ve settled on four 3/16” 316 stainless bolts holding a 1” thick insulating panel to a 19mm thick timber door with the panel held off the timber with a 3 mm bead of Permatex to reduce conductive heat transfer. My solution is one of many and the downside with my design is that you cannot place the door at pizza temperature after a big cook up and leave it in place overnight to reuse the oven the following day. Or the timber will burn. I need to wait until the oven has cooled down to under 300C (why would you roast or bake anything above 300 C anyway). I just really like the look of a timber door and its traditional link.

Only trial and error can be your guide.

[IH123]

I shouldn't have said thin. I meant thinner just because the outer face wont be facing the flame. considering using 1/8" for the outer door face. the prematex high temp silicone/RTV has less temperature rating rating than fiber glass gasket so I would still favour a design with fiber glass gasket if I could.

today, I had the chimney stainless steel adapter bolted to the chimney refractory brick base with the stainless steel bolts, nuts, washers, and lock washers and had fiber glass gasket between it and the bricks. the bolts had ceramic fiber paper around hem everywhere. I stopped warming the oven with electric heater as bricks appear dry, I use an outdoor rated shed shelter on the oven so it can be snow ready and protected as I will shovel snow from it, I placed extra tarps on top as well. I seasoned the steel door inner plate. here is the design I am considering for the door:

[Giovanni Rossi]

the prematex high temp silicone/RTV has less temperature rating rating than fiber glass gasket so I would still favour a design with fiber glass gasket if I could.

Not to beat this dead horse, but for clarity for new builders:

Permatex Optimum Red RTV Silicone Gasket maker has a continual service temperature range up to 750°F (399°C). It can withstand spikes up to 1000°F (538°C) for an hour or so.
In my application I have not seen any signs of degradation over the past year. I place the gasketed steel door against the inner arch after a pizza session while there's still a large bed embers. I don't recall ever seeing thermometer in my door register over 550°F (399°C).

Fiberglass gasket does indeed have a higher temperature tolerance. In fact, I tried that first. Note, my application was different than your design and the gasket was exposed to abrasion. I found the gasket was easy to shed fibers, especially at the cut ends. I didn't want those tasty tidbits on the bottom of my pizze. I originally got the Permatex to seal the ends of the fiberglass and then realized I could simply replace the fiberglass entirely.

In the words of david s, "Only trial and error can be your guide."

[IH123]

Not to beat this dead horse, but for clarity for new builders:

Permatex Optimum Red RTV Silicone Gasket maker has a continual service temperature range up to 750°F (399°C). It can withstand spikes up to 1000°F (538°C) for an hour or so.
In my application I have not seen any signs of degradation over the past year. I place the gasketed steel door against the inner arch after a pizza session while there's still a large bed embers. I don't recall ever seeing thermometer in my door register over 550°F (399°C).

Fiberglass gasket does indeed have a higher temperature tolerance. In fact, I tried that first. Note, my application was different than your design and the gasket was exposed to abrasion. I found the gasket was easy to shed fibers, especially at the cut ends. I didn't want those tasty tidbits on the bottom of my pizze. I originally got the Permatex to seal the ends of the fiberglass and then realized I could simply replace the fiberglass entirely.

In the words of david s, "Only trial and error can be your guide."

I will use Permatex Optimum Red RTV Silicone to seal around the fiber glass gasket. I am designing my oven for 1000F , which may not reach, however trying to keep nothing less than 1000F. I totally missed that fiber glass, even when outside of the door, can still shed fiber on archway when door is moved around and may not be noticed in tiny quantities. Thanks for the info, I am sure the silicone will prevent fibers shedding out and if it degrade then I will reapply.