Update on my floor which exploded from steam re wet insulation

[lwood]

Re: Update on my floor which exploded from steam re wet insulation

I never caught what kind of insulation was underneath the floor that exploded. Been on this forum for three years now and never seen that before. Was it perlite/concrete mix in according to this forums specs? Lots of discussions on that. Can't imagine that would absorb enough water to explode, unless water is getting in from somewhere else.....like rain. Don't tell me it was a thermal blanket insulation. This information would be very valuable to know so we can prevent it from happening again and someone getting hurt.

[NJOven]

Re: Update on my floor which exploded from steam re wet insulation

Unknown, but the removed insulation was soaking wet.

[lwood]

Re: Update on my floor which exploded from steam re wet insulation

It sounds like you have it all dried out now, so maybe it will be ok. The delta T btw the dome & floor demonstrates your insulation problem. The dome being at 950 and the floor at 750 is a very big temp difference. Usually is is less than 50 deg F. But if it works, it works. Not very efficiently but, whatever. To do it write, you need to tear down the dome and put 4" of insulating (perlite) concrete, to the specs on this site, and rebuild the dome.

You need to understand that these ovens are much more than just brick and mortar, they are refined proven designs, which if you skip one crucial step, like you did, they don't work properly. You need to follow all the specs from this site. There is a vast community of professionals here on this forum and they know of what they speak.

You definitely won't get the perfect Margarita pizza with that delta T. You will have trouble getting the tops and bottoms to be ready at the same time. If it works for you then plow ahead and make Pizza. Don't recommend any long slow cooking or roasting, the concrete slab will suck the heat out of the oven very quickly. And using a lot of wood. Just 5 or 6 pizzas and a roaring fire for a couple of hours, it should be ok.

[shuboyje]

Re: Update on my floor which exploded from steam re wet insulation

Not to be confrontational, but I couldn't disagree more. Heat rises, naturally the top of the oven is going to run hotter. That temperature difference is important for a balanced bake, especially in the higher domed Pompeii ovens most here have. The hearth transfers its heat directly via conduction. The dome transfers heat to the top of the pie via convection and radiation. Much less efficient, therefore requiring more heat to achieve a balanced bake. His temperatures are perfectly inline with what I would expect. The rapid heat lose and fact that the hearth is only getting to 750F would be my bigger concerns. I would expect numbers along 900F hearth and 1100+F In the dome.

[WJW]

Re: Update on my floor which exploded from steam re wet insulation

I have to agree with shuboyje on this one. When I am heating the oven my vault arch (dome) is MUCH hotter than my hearth. Typically well over 1100 at the dome when things are really going...and I've seen it hit over 1300....with the hearth anywhere from 950 to just over 1000.

When I get ready to start pizzas, I push the coals to the side, brush the hearth with a brass brush, then wet scrub it with a natural fiber brush. I then throw a couple of two inch diameter logs on the pile of coals to give me active flame hugging the arch and radiating toward the hearth. I then have to wait about five minutes or so for my hearth to come down to something in the 850-900 range. At that point my vault arch is typically at around 1000, or just over.

Lately I've been waiting significantly longer for the hearth to cool (maybe thrity minutes) because I've been trying to cook most of my pizzas with my hearth at around 775 and my vault arch around 900. I realize this is a bit on the cool side for the hearth for Naples style, but it seems that most of the pizzas that go in my oven lately have had a lot of toppings and are relatrively wet. With that kind of pizza and a real hot hearth I find my bases get done well before the toppings are cooked. For a true Naples style with very light toppings, I prefer a hearth of around 825-850 and a hot vault arch of about 950-1000. That will give me a true ninety second pizza. With the thicker ones I have to stretch it out to about two and a half minutes to get one that is properly cooked all the way through.

For those that haven't done a lot of pizza cooking, the pic below shows what you are looking for on your dome/vault arch while cooking pizzas. That vault is probablly around 950 or a bit hotter on the right

(The upper portions of the walls on the left, and the left portion of the vault is obviously less than 750 degrees or so at the time the pic was taken as carbon is present...I don't recall for sure but, based upon the fact that bricks are clear down low on the left side, and covered in carbon up high, I would guess that the oven had previously been completely clear, but that the left side wall had cooled because it is farthest from the flame, and then we built up carbon high on the walls from burning screwed up pizzas off the hearth. Because the left side had cooled somewhat by that point, the carbon didn't burn off there. You can see how much heat is coming off the hearth though, because even to the extreme left side, we have no carbon down low.)...



I would think that njoven should have no problem cooking pizzas. He will have a tougher time reaching and holding real high temps because of the lack of insulation, but pizzas cook fast, so it's not that big a deal IMO. He'll have to recharge more often by raking coals on the hearth, but he'll be able to get the job done.

Where I think he'll run into problems is low temp retained heat cooking and for bread. If I close my oven up after cooking at pizza temps at nine pm, I'm still too hot to cook bread twelve hours later. (Typically around 625-650 degrees if the oven had been fully charged and closed up hot.) Now that really isn't an issue because I bake bread in the afternoon after letting my sourdough rise in the morning...but it's amazing how hot it stays. But in njoven's situation, it doesn't sound like that is all that big a deal because he isn't planning to bake or cook pork shoulders, etc.

njoven...have you taken any temps the day after cooking to see how it holds heat? Id be interested to hear in order to get some real number comparisons on how big a difference the hearth insulation actually makes in retaining heat over a period of one to three days.

Bill

[lwood]

Re: Update on my floor which exploded from steam re wet insulation

"The rapid heat lose and fact that the hearth is only getting to 750F would be my bigger concerns"

When an oven is at equilibrium and fully charged, there should never be a 200 deg difference btw the dome and the hearth. The fact that is the case shows how the concrete slab is sucking the heat out. You said it shuboyje.

[shuboyje]

Re: Update on my floor which exploded from steam re wet insulation

I agree it is leaking heat out the floor. No doubt about it, but without insulation that is a no brainer.

As for the temperature difference are we talking about the same thing? You have mentioned an oven in equilibrium twice. I am talking about an oven actively cooking Neapolitan pizza in under a minute. If my dome was the same temperature as my hearth while I was trying to cook pizza I would be VERY disappointed and would not cook the pizza, I would wait for the oven to come into proper balance for pizza cooking with the dome hotter then the hearth. I know things are a little different in a higher domed hemispherical oven, but that would only increase the need for a greater temperature on top.

I'll one up for WJW, here is a very short video of my oven with the type of flame used for cooking very fast baked pizza and the 40 second pie it produces:

Convection in a wood fired pizza oven - YouTube

Aren't pizza ovens fun!?

[lwood]

Re: Update on my floor which exploded from steam re wet insulation

We vehemently agree. Nice pizza, looks like you are at 1000deg F. Little too hot for me....of course I am old and slow.

[NJOven]

Re: Update on my floor which exploded from steam re wet insulation

it seems I stepped in the middle of a master oven guru debate??? For what I Need this oven for--it seems to be working just fine--not optimal, but the pizzas were delicious and I am not into bread baking. Heat retention is not great the next morning, but I am not concerned about that for my intended use and the oven may still be drying out.

There is no way I am rebuilding the dome at this point.....

[WJW]

Re: Update on my floor which exploded from steam re wet insulation

Killer video shuboyje! Do you actually cook under that much flame? If so...wow. I haven't even attempted to cook under that much.


njoven...I am so far from a master oven builder it's not even funny. In fact, as far as building goes, I have built a total of ONE. And that thing is full of mistakes. I have cooked in it a lot in the past three months or so....but nothing like what others around here have done.

Bill

[Tscarborough]

Re: Update on my floor which exploded from steam re wet insulation

The most important aspect of any oven (or any other home improvement project) is that it performs to your expectations and needs. It sounds like you are well sorted, enjoy it! I still want you to send that mason over to talk amongst other masons about his wrong convictions regarding oven building.