Need help before i demo my oven and start over

[daniel5455]

Yesterday i wanted to make pizzas in my oven and it failed me.

My base is constructed of the following.

2.5" of portland and sand then on top of that i did 2.5" of vermiculite cement.

Then the oven floor is made from fire brick. and i built the dome around the floor. i have a inner diameter of 34 1/4" the door opening is 18 1/4 " by 14 1/4" high. Im not sure of the height of the dome.

I live in chicago so the weather here sucks. but Yesterday was not too cold but was windy. The problem im having is that its taking too long to heat the oven ( I use alot of wood) and second the oven floor doesnt stay hot long enough. Yesterday i had the oven around 800 degrees and the floor was only 300 deg F. I also have insulfrax wrapped around the dome. not in the pics though. Here are some older pictures of the oven but still looks the same. Anyone have any suggestions or do i need to pull out the sledge hammer and start over?

[Neil2]

Re: Need help before i demo my oven and start over

Don't give up yet. A new oven takes a lot of firings to cure.

Make sure that your wood is well seasoned, this is critical.

You said your dome is 34 1/4 inches in diameter. Assuming that it is a hemisphere, the dome height would then be 17 1/8 inches. The rule of thumb is that the door height should be 63 % of the dome height = 10 3/4 inches. (The door width is not critical).

If your door height is 14 1/4 as you stated then this may be too high. Is it possible to fit some kind of insert to effectively reduce your door height to 10 3/4 ? Otherwise your construction and insulation looks fine. The dome brickwork looks well done.

[Jed]

Re: Need help before i demo my oven and start over

Daniel5455,

With a new oven, you have a noticeable amount of water in all the masonry that was used.

For my oven, after the curing fires, it took at least 10 heating cycles - pizza cooking cycles, before I was satisfied with the performance of my oven. I had very similar impression from my oven as you are expressing with yours...

Give WFO's a chance!

JED

[dmun]

Re: Need help before i demo my oven and start over

Yes, two and a half inches of vermiculite concrete is on the low side (four is recommended). If all else fails, you could pull out the floor bricks, put in an inch of cal-sil board, and replace the floor bricks. Easier said than done, I know.

That said, a lot of ovens have no insulation under the floor (we know, we hear about them after the fact) and they somehow get them hot enough to burn white. So first try drying out your oven really well.

[Neil2]

Re: Need help before i demo my oven and start over

Dmun - there is only 3 inches of heat exchange space above the door height.

[daniel5455]

Re: Need help before i demo my oven and start over

Here are the exact measurements. 34" diameter inside. Dome height is 25" from center of floor to top. the Door Measures 18.5" wide by 14" high by 17.5 " deep. If these measurements are ok then can someone please explain in detail with times and degrees on how to start the fire the correct way from starting the fire in the middle to when to move the fire to the side and what degree should you start making pizza's I will post some more pics with the fire going and a pizza inside of the oven

[Neil2]

Re: Need help before i demo my oven and start over

If you are still in the curing stage try this thread:

http://www.fornobravo.com/forum/f16/...uring-767.html

After it was cured, my typical firing technique (for a 40 inch x 18 high dome) is as follows:

Pizza minus 90 min: light smaller "campfire size" fire near front of dome. Keep fire steady but small.

Pizza minus 1 hour: Push back the small fire to the middle of the dome, load it up. Mine uses approx 1 cubic foot of fire wood - pretty much all I can get in. Put it all in at once. You should end up with a fierce fire (remember the "Plasma God" from startreck). The flames should be licking out the top of your door and out the tunnel.

Pizza minus 15 min. Rake coals and fire to the side. Brush and swab hearth. Put door on and let soak for 10 min. At this point, the dome temp is 1000 degrees and the floor temperature is 800 degrees. Put door on and let soak for 10 min.

Cook pizza. The first pizza will char a bit. The rest cook OK. I generally do not have to add any more wood to cook 10 to 12 pizzas.

Your dome height is, I think, unusually high for a Pompeii oven. Typically the height is at most half the diameter (17 inches in your case) or even lower - some suggest 90% of the radius. I don't know what effect your high dome may have on your firing/cooking cycle. Maybe some others might have more info.

You could possibly insert a 1 inch insulation layer and another 2 1/2 inch thick fire brick layer in your existing hearth, this would leave you with a 21.5 inch dome height and a still workable door height of 10 1/2 inches bringing the proportions somewhat closer to the "ideal".

[Jed]

Re: Need help before i demo my oven and start over

And my oven takes closer to a full two hours to get up to pizza temperatures. Either I didn't insulate as well, or the wood that I use (and my fire making skills) don't release as much heat into the bricks as fast, what ever. The reason why sort of doesn't make any difference.

What is important is that if I want to get my oven up to pizza temps, I start a fire a couple hours before, and keep as much fire going as I can. I have to start the fire near the front of the oven because my arms aren't long enough to fiddle with the details back in the middle of the oven. But after the fire is well established, I will push it back into the middle of the oven and load up the wood to let burn in the middle of the oven.

The clues that my oven is hot include the 'dome going white', and then the readings from the IR thermometer, in the 900+ degree range for a period of time...

Then the just like Neil, I'll push the fire to one side (or the back - still experimenting with the system that works best for me...) and will toss on bits of wood as I want to keep the temperature as hot as necessary.

And really the only reason I know to run the fire in my oven longer than Neil runs the fire in his oven is through trial and error. As in experience with this individual oven....

So I'd say, build a big fire (monster flames spilling out the dome) in the oven, keep it that way for awhile (the dome goes full white, then keep the big fire for another little while) then cook some pizza!

And report back - with pictures!

Best luck

JED

[daniel5455]

Re: Need help before i demo my oven and start over

Here are some pictures.


This is how i start the fire


Fire going after a few min.



You can see smoke comming from the seems that tells me that there is moisture underneath.


You all have been a great help i think the issue is that im not getting the dome hot enough it never turned white. I didnt relize that you need to use alot of wood.

[daniel5455]

Re: Need help before i demo my oven and start over


This is underneath the base. The plywood never fell. Im thinking of stapling insulation to the wood to prevent air from comming in the bottom and cooling the base.





the floor temp was only 450 deg F

[Jed]

Re: Need help before i demo my oven and start over

Daniel5455,

If you are still boiling steam out of the floor, you still have a ways to go before your oven is ready to cook.... The steam, and moisture pull the heat from the structure and will prevent you from attaining and maintaining higher temperatures.

Build another half dozen or dozen fires in the oven over then next couple three weeks, then start to get critical about performance...

JED

PS: Insulation under the structural floor probably won't add much in the way of performance benefits....

[Neil2]

Re: Need help before i demo my oven and start over

Don't worry too much about a little smoke escape and steam. If there is a lot of steam, consider slowing down your curing process a bit.

When it is cured and you get to the full firing phase, I would use about 3 or 4 times as much wood as shown in your first photo. Stack it in "teepee" fashion for a quick full burn.