Update on my floor which exploded from steam re wet insulation

[indiebands]

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

This is what you call hijacking a thread

I started getting the new floor exposed to heat. 3 days of warming fires. Ran the oven for 40 mins with 2 medium logs and got dome up to 450 and floor 250--it's a 40" floor and oven has a lot of overhead mass. 2 more days to drive out any residual moisture in dome (when floor exploded, there was tons of moisture underneath), and I will go up to plasma fire levels.

Fingers crossed.

Hi NJOven,

Apologies for the thread hijacking. I thought of it more as "leveraging" or tapping into the existing base of expertise on this topic. Actually, I was reassured by reading that others had similar issues and that there are so many experts out there willing to share ideas.

Now that I am reassured and a little less hysterical, I will un-hijack the thread and move it to a new home.

Thanks for your patience and the good ideas!

[NJOven]

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

thanks. Will run a big, long fire today as need to get any residual moisture out--want to make my first pizzas tomorrow--but this oven needs to run alot hotter. After 3 hours yesterday, was only hitting near 800 at the dome, and 500 on the floor.

[david s]

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

Yes to both questions. It takes more fires than you would think.

[NJOven]

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

UPDATE:

After 3 days of moderate warming fires, I attempted to go plasma fire today. The first hour wasn't a huge fire, 2nd hour I was burning it big, 3rd hour medium-big re the fire/logs. After 3 hours, I had 800 on the dome, and 500 on the floor. It's a 40" floor and an oven with a lot of mass that really hasn't been used in over 16 months until I blew up the floor last week (see earlier in thread).

Noticeably, I had some visible wet spots appearing on the bottom of the floor after 3 hours today that were damp to the touch. Each spot was approx 2" in diameter. Temp of the underside of the floor was only 110 degrees after 3 hours of fire. As a reminder, floor is 1.5" fire brick, 2" fire clay, and approx 2" concrete. The mason did not add insulation under the floor (no more bashing please, I get it now....)

Tomorrow I will burn the oven again to see if there is any more water to burn out. Is it normal to see the water leave via wet spots appearing underneath? How much of a factor will water cause towards not reaching higher temps?

Thanks--this board is a great resource and appreciate the feedback!

[WJW]

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

Oh. Got it now.

[Neil2]

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

"I thought I read that his mason had already cut down into the slab"


WJW

This thread somehow is discussing two different builds. The original one by NJOven and a later one by Indie bands.

[WJW]

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

I thought I read that his mason had already cut down into the slab, removed two inches of concrete, and then filled that depression with fireclay.

If I read wrong, then I agree with Neil. But if it really is just two inches of fire clay sitting beneathe the hearth bricks, it seems like a no-brainer to replace that fireclay with ceramic fiber board insulation.

The "bathtub" thing is a good point. If your mason really did cut out two inches of concrete under the hearth, it probably would be worth using a rotohammer to drill a hole or two every foot. It would promote drainage of any water that would get in, and would do nothing as far as heat loss goes.

[Neil2]

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

Indie bands

I would not cut down into the slab. Apart from the structural issues that David raises, you will create a permanent "bath tub" that will trap and hold any water that gets in.

In addition it sounds like it would be very difficult to do with any degree of precision.

If it was my oven, I might try a gradual incremental prying and wedging process to raise the entire oven off the slab and inch or two and slip some insulation board under.

[NJOven]

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

Bill,

Thanks for your reply. Will give this a shot for a bit and if it doesn't fit the need, will find another guy in NJ to rip out brick and fireclay and add insulation. Luckily the walls do not rest on top of the bricks.

[WJW]

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

NJ Oven

Throwing my two cents in here...I think you will find it is worth it to try to add some insulation under the floor.

That being said, you will be able to cook pizza in your oven without adding insulation. You will probably be limited to cooking a couple pizzas...then re-charging the heat in the bricks by putting a layer of hot coals on them for four or five minutes...cooking more two more pizzas, and so on.

Obviously, if you burn wood in there long enough, you will eventually so saturate that five inch slab that it will hold enough heat to allow you to cook a whole bunch of pizzas. The problem is that you really honestly could have to burn a hot fire for three, four, or more hours to reach that level of saturation in the slab. And even if you do that, the problem is that once saturated, the bottom of your slab (top of your wood storage area) will now be very hot and will be radiating a tremendous amount of heat downward into the storage area. This obviously continues the process of bleeding heat away from the cooking surface...and potentially creates issues with storing wood down there. (If the ceiling of your storage area gets hotter than 250 degrees, I'd be concerned...but I honestly don't know enough about that to know the potential danger there.)

If there is anyway possible to get two inches of fiberboard insulation between your hearth tiles and that slab, you will see an incredible difference. Consider how well a top quality thermos keeps a quart of coffee hot, as compared to how an uninsulated milk carton would keep that same quart of coffee hot. The coffee in the milk carton will be at room temp in four or five hours....the coffee in the thermos will be hot the next day. Insulation makes an even bigger differnce in an oven because the relative temp differentials are so much greater.

If it were me...I'd pull the 1.5 inch thick firbricks out. Then I'd put a two inch thick layer of top-quality fiberboard insulation down. (Now you are half inch "above grade.") Then I'd place full thickness firebricks on their side in a herringbone pattern (so you won't have any right angles to catch tools on). Then you'd be three inches above grade. Far from ideal, and it may make your door a bit low, but at least it will cook like an oven.

Before you do this you will need to do some door height to oven height ration calcs and see how far from the ideal ratio you are going.

Assuming you can pull that off, that would give you a 2.5 inch thick floor which is isolated from the stand/slab/ground and which would hold heat very well while still maintaining adequate thermal mass.

That's my opinion.

Bill

P.S.: I don't mean this as an insult to you so please don't take it that way: Your mason is an idiot. He may be a wonderful mason, but he doesn't know squat about ovens. He totally screwed you over by building you an oven which, yes, will cook a pizza, but it isn't even as remotely efficient or versitile as it should be. I could cook a pizza with a blow torch and a metal lunch box....but that doesn't make it a pizza oven. ...And worst of all...you apparently wanted to put insulation in, but he apparently talked you out of it!!!

Edit....I just read your post that said your mason took two inches of concrete off the slab and replaced it with two inches of fire clay!!! You're in much better shape if that's reeally what he did. I can't imagine why he would do such a thing, but I hope he did. Fire clay is no insulator...it might as well be concrete as far as that goes...but it should be super easy to remove! Pull that fireclay out and replace it with a two inch layer of fiberboard insulation. You'll be fine if you do that.

[NJOven]

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

This is what you call hijacking a thread

I started getting the new floor exposed to heat. 3 days of warming fires. Ran the oven for 40 mins with 2 medium logs and got dome up to 450 and floor 250--it's a 40" floor and oven has a lot of overhead mass. 2 more days to drive out any residual moisture in dome (when floor exploded, there was tons of moisture underneath), and I will go up to plasma fire levels.

Fingers crossed.

[indiebands]

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

Indie bands,
By my calculations your door height to dome height is 68% so if you raised the floor by 3" then you would end up with a ratio of 60% which will work quite ok. I think trying to dig out 3" of the concrete slab would be way too hard and it may weaken the slab enough to risk collapse. You will still have the problem of the dome sitting, uninsulated on the supporting slab, but that shouldn't matter as much as getting the floor insulated. Just getting the four floor tiles out will be a trial I imagine.

Another thought - is there a minimum floor tile thickness in order to retain the heat and cook? The supplied floor tiles are 6cm thick. If I could replace them with a thinner floor material, then the insulation would take up less of the oven height. Finally, is there a minimum usable door height?

Thanks again to all.

[indiebands]

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

Good luck.

Thanks. I'll need it.

[david s]

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

Good luck.

[indiebands]

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

Indie bands,
By my calculations your door height to dome height is 68% so if you raised the floor by 3" then you would end up with a ratio of 60% which will work quite ok. I think trying to dig out 3" of the concrete slab would be way too hard and it may weaken the slab enough to risk collapse. You will still have the problem of the dome sitting, uninsulated on the supporting slab, but that shouldn't matter as much as getting the floor insulated. Just getting the four floor tiles out will be a trial I imagine.

Thanks, David. I know that the dome itself would still be uninsulated, but figured that at least by surface area, insulating under the floor would help (better than nothing). According to the schematics the floor pieces should be 1 cm narrower than the door, though I too am worried about getting out the floor tiles. It looks like concrete saws are probably too big to fit in the confines of the oven dome...

What about cutting in from the sides, putting in supports, inserting an insulating board (1/2 at a time) and then reinforcing the outside structure. Sounds a bit like science fiction.

Keeping my fingers crossed.