Update on my floor which exploded from steam re wet insulation

[NJOven]

Recap from a prior thread---

Well, after 1 hour, got floor (40") up to 600 near coal beds and was 350 in coolest areas near opening. Then heard a boom and a fist sized chunk of the floor popped out!!! Disappointed as I did 3 days of prior warming fires as the oven hasn't been used in over 14 months. Plus, with this house I bought last July, the contractor they used for many things was awful...

Update---

The broken floor was a 4/quadrant tile floor of refractory concrete with wet insulation underneath. I suspect it was wet from a prior leak I fixed 6 months ago and the oven hadn't been used in over 16 months.

The new floor is 1.5" fire brick and the mason, who has been building brick ovens for 20 years as a 3rd generation mason, felt very strongly about not using insulation under the new floor. The new fire bricks are set on top of 5" concrete over the hearth/receptacle which holds the firewood. I had some reservations re not adding insulation under the firebrick floor, but the mason was adamant. Did I make a mistake here? If so, how important is the insulation under the floor?

Thanks

[GianniFocaccia]

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

Insulation under the floor critically vital to the performance of your oven, not only from attaining operating temperature, but also for retaining valuable residual heat. An oven without floor insulation will leak all the heat you can put into the floor as fast as it can through conduction to the concrete below.

There are others here who have found themselves in your position, and the recommendation, across the board, it to retrofit some (any) insulation under the floor.

The first thing I would do though, is get a new mason.

[SableSprings]

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

As noted in many other threads in this forum, the concrete will act as a heat sink for your fire and coming up to/and holding temp in the oven will be much more difficult than with an insulated base for your hearth. It is interesting to look at what most people here wish they could/would do differently if they were building again...a solid majority say MORE INSULATION (both top & bottom).

Although your mason may have been building wood fired ovens for a long time, he hasn't been keeping up on making them efficient. I think you need to look for a new person for your next masonry project.

(Looks like John - GianniFocaccia above - and I were commenting at the same time...glad we both gave you the same advice...)

[Ken524]

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

edit: Oh my! Three of us posting nearly identical posts simultaneously.

...felt very strongly about not using insulation under the new floor. The new fire bricks are set on top of 5" concrete over the hearth/receptacle which holds the firewood. I had some reservations re not adding insulation under the firebrick floor, but the mason was adamant. Did I make a mistake here? If so, how important is the insulation under the floor?

NJ,

You can't have enough insulation. The most important place to insulate is between the oven floor and concrete slab.

All too often on this forum we hear from owners that had "a really experienced mason" tell them they don't need insulation. They wonder why their ovens don't heat up in 90 minutes and crank out pizza all night long.

Mason's are amazing craftsmen that can do magic with brick and stone. I always stop and watch, in awe, when I see these guys slinging bricks and mortar. Unfortunately, many of them don't understand thermal mass and insulation.

If the floor bricks are touching the 5" thick concrete slab, then you will be heating not only your cooking floor but the the 5" thick slab underneath it. That's a LOT more mass which means it will take a LOT more wood and time to get your floor to a reasonable cooking temperature.

The 5" slab will act like a giant heat sink and suck the heat right out of your floor bricks. It's easy (and fast) to get one layer of bricks heated to 800F. Now think about what's involved in getting 5" of concrete PLUS your floor bricks heated to 800F. It might take so long to heat your oven that it won't be worth using.

You really, really need to have insulation under the floor. The oven will heat up faster, use less wood, and retain the heat better for baking.

If you can remove the bricks and add insulation, you'll be far better off in the long run.

[Laurentius]

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

You did a bad, bad thing.

[NJOven]

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

Well, it is what it is at this point. Spoke to references that also don't have insulation and they don't have an issue cooking pizza in 2 mins with their ovens-- none of which have floor insulation. Appreciate the reply, will see once floor cures and I warmup the oven.

[Ken524]

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

Temperature is temperature. When the oven is up to speed, a 9" thick floor heated to 800F will cook the same way a 4" one will. It's simply a matter of how much time and energy are required to get to that point.

We aren't trying to beat you up. Keep us up to date and let us know how it works for you!

[NJOven]

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

Temperature is temperature. When the oven is up to speed, a 9" thick floor heated to 800F will cook the same way a 4" one will. It's simply a matter of how much time and energy are required to get to that point.

We aren't trying to beat you up. Keep us up to date and let us know how it works for you!

Thanks. Wasn't taking it that way. My primary use of oven will be to cook for an hour or so once I get it up to temp. sounds like it may take me 2 hours or so to get up to temp rather than 60 mins. I really wouldn't have use for cooking he next morning with retained heat--I don't have the time on my hands for that. Just want a functional oven for pizza and paella. Again, this guy was adamant and had built a lot of ovens in the area but I can't argue against what I don't know.

Btw, the insulation he pulled out was SOAKED and this was after 3 warming fires and a big one which blew out the floor.

Again, appreciate the feedback.

[Tscarborough]

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

Many 20 year masons make the same mistake. And it is a mistake. If you can get more than 1 or 2 2-minute pizzas without having to recharge the floor, I would be surprised. Please send your mason here, or even better, to contractortalk.com and ask him to give his opinion of no insulation under the floor. I would like to save others the same problem.

[NJOven]

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

I just called the mason and my info was not correct. He did not replace the soaked floor "insulation" like he pulled out, but he took out part of the 5" concrete under the floor such that 2" fire bricks sit on top of 2" fire clay which is on top of 2" concrete. He abhors insulation and has been doing this a long time.

[Tscarborough]

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

Well, he is wrong. Flat wrong, no question about it. Send him to contractortalk.com and ask him to post in the masonry forum.

[NJOven]

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

I just called the mason and my info was not correct. He did not replace the soaked floor "insulation" like he pulled out, but he took out part of the 5" concrete under the floor such that 2" fire bricks sit on top of 2" fire clay which is on top of 2" concrete. He abhors insulation and has been doing this a long time.

Well, he is wrong. Flat wrong, no question about it. Send him to contractortalk.com and ask him to post in the masonry forum.

I don't know if you are trying to help me or defend something else as your reply is, frankly, a bit confrontational. You didn't even respond to my factual correction on depth of materials and use of fire clay. Not looking for an argument here, but seems a bit cultish here???

[Tscarborough]

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

Not confrontational to you, but to your mason, very much so. He is wrong, and not insulating under the hearth is not only wrong, it is simple common sense. I would like to convince him he is wrong so he will quit building ovens incorrectly. In my job I have to deal with it, and believe me, it sucks to have to tell someone that their brand new 5 or 10 thousand dollar oven will never perform as expected, even though it was built by a 20 year mason. Just because someone does something wrong for 20 years does not make it right.

[david s]

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

2" of fireclay will act as a good leveler for the floor bricks, but not particularly good as an insulating layer unless he added around 50 % vermiculite. Can't understand why any oven builder would abhor insulation, it is fundamental to the efficient functioning of any oven.

[texassourdough]

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

As someone who has a leaky hearth (built on a Scott style hearth) I would expect you to be able to do pizzas without too much trouble - but you will likely find you need to recharge the hearth every couple of pizzas OR keep a pretty big fire going or both. Oven management will take more attention. Your biggest limitation will be that you will not retain heat well for retained heat cooking and baking.