Floor modification

[ShannonCorum]

The inside height of my oven is 17 inches. I don't have any insulation under my firebrick floor. It's basically 2 1/2 firebrick over my concrete slab which is 5000psi concrete reinforced with rebar. Since I can't rip up my floor, I'm trying to figure out how best to increase the function of my floor. I placed a 1 inch fiberboard and firebrick splits on top of it. That decreased my inside height to 15 inches. While the fiberboard I'm sure helps to protect my concrete slab underneath from the heat, but I don't think the splits hold heat very long. Someone suggested I add another layer of firebricks on top of all that for another 2 1/2 inches on top of the fiberboard. While that will certainly increase the thermal mass of my floor, I don't like decreasing my inside height even more.

I'm debating on taking out the fiberboard and splits and just putting a second layer of firebricks on top of the original floor. That will be a total of 5 inches of firebrick on top of the concrete slab.

Or, should I just take all the extra crap on top of my original floor and leave it be.

Can anyone offer any opinions on this, aside from ripping it down.

Thanks,

Shannon

[brickie in oz]

Re: Floor modification

I'm debating on taking out the fiberboard and splits and just putting a second layer of firebricks on top of the original floor. That will be a total of 5 inches of firebrick on top of the concrete slab.

How is adding more mass helping with the insulation?
Pull it down and build it properly, you know its the way to go.

[WJW]

Re: Floor modification

Why can't you rip up the floor?

Your options are extremely limited. If you want to place insulation between the hearth and the slab, there are only three ways to do it. You can either tear the entire oven down and start over, build a false floor as you seem to be doing (but you need an actual layer of insulation in there with masonry of sufficient thickness to hold some heat), or you can rip up the floor as best you can.

As Al notes, doubling up on the firebrick layer will do nothing to stop heat loss. All you will have done is to make your slab 2.5 inchs thicker. You already have all the mass you need...an entire slab's worth of mass.

How are your hearth bricks placed? No way to pull them up and then lay down a couple inches of ceramic fiberboard insulation? Then set bricks on top of that?

Bill

[nissanneill]

Re: Floor modification

There is no easy way to solve the problem that you built and need to accept responsibility for!
There are really only 2 ways around your problem, sorry 3 ways! The last way is to put up with what you have. the second is to demolish it and rebuild as per the free Pompeii plans and my way is a little more risky but I would attempt it first.
It involves knocking out 4 bricks at the floor level and inserting 2 I beams parallel to each other and protruding a foot out on each side. You will need to fabricate 2 internal braces which will bolt securely through these beams to make a rigid lifting frame. Now you need to use a forklift, a scaffold or a triangular frame with a substantial block and tackle to lift the dome up allowing you to do your hearth changes. To make the exercise safe to work beneath, you will need to support the frame with bricks/blocks under the lifting points leaving enough room to get in and repair the problem.
You should have the main beams a little longer so as to provide support for the entrance arch bricks. Before you lift the oven, you will need to cut through most of the cement mortar of the bottom row to reduce the possibility of collapse when you lift.
Once lifted, you will need to support the mass well and be organised to get your modifications done quickly and in one session as the domes are not designed to be supported as suggested. You can also squeeze inside to place supports within the dome if you feel so inclined.
Success is dependent upon the strength of the mortar you used, but even using rachet straps around the base bricks will improve your chances of success!
Once lowered, you simply mortar in replacement bricks, repair your insulation, dry it out and enjoy, all achievable in a good day's work.
I would also rebuild it with the hearth bricks inside of the dome rather than under the dome bricks so that any future problems can be easily sorted.
Food for thought.
Cheers.

Neill

[david s]

Re: Floor modification

"Why can't you rip up the floor?"

It's amazing what you can do with a crowbar, a pinch bar and an angle grinder with a diamond blade.

[ShannonCorum]

Re: Floor modification

We are considering that.

[ShannonCorum]

Re: Floor modification

Someone on here, I think, once advised me to insulate under my existing concrete slab, instead of adding stuff on top of my oven floor. This would certainly conserve my inside dome height. I kinda see the logic, if the concrete is acting like a heat siphon, wouldn't insulating under it help that?

I actually bought some Rockwool a while back but then tried the fiberboard inside instead.

Would insulating under the concrete slab help?

Thanks,

Shannon

[mrchipster]

Re: Floor modification

Someone on here, I think, once advised me to insulate under my existing concrete slab, instead of adding stuff on top of my oven floor. This would certainly conserve my inside dome height. I kinda see the logic, if the concrete is acting like a heat siphon, wouldn't insulating under it help that?

I actually bought some Rockwool a while back but then tried the fiberboard inside instead.

Would insulating under the concrete slab help?

Thanks,

Shannon

If you decide that insulating under the slab is your final solution you better have a large forest of wood to burn and lots of time to feed wood into the oven prior to cooking because I asume the slab is connected to the vertical walls of the foundation and they will be wicking heat away also.

I have 4.5 inches of insulation under my floor bricks and I still find that heat wicks into the structural concrete slab, I wish I had another 2 inches of insulation under my floor. But I can heat my oven in less than 90 minutes to Pizza temps and it will hold enough heat to cook for up to 6 days in the summer and 4-5 days in winter.

Just bite the bullet and rebuild, As Brickie says.

Chip

[ShannonCorum]

Re: Floor modification

I went with David's suggestion. We are ripping up the floor and will put insulation down and then a new floor on top. I just happened to have a root zip with a diamond blade, a crowbar, and a Mason's chisel. My husband has done most of the hard labor, but he's gotten about 95% of it up. Leaving a nice hole to fill with vermicrete.

Shannon

[WJW]

Re: Floor modification

You have already said that you are tight on space...I'd srongly consider ceramic fiber board rather than vermicrete. I don't know exact numbers but it has about twice in the insulating vaule. If you are limited to only two or three inches of insulation I'd lean toward the fiberboard.

Bill

[ShannonCorum]

Re: Floor modification

Okay. I'll look in to that. I would have about 3 inches to fill under the new floor.

Shannon

[WJW]

Re: Floor modification

If you had three inches of ceramic fiber board under the floor, with 2.5 inch thick fire bricks sitting on top, your oven would be extremely well insulated. I have 3 inches of insblock 19 sitting on my slab, with the bricks sitting directly on the Insblock. It stays really hot for days.

If I cook pizza and close it up when it's seven hundred or so, it will still be between 550 and 600 the following morning. Morning two it's 375. Morning three it's 250-270 (perfect for ribs, pork shoulder, osso bucco). Morning four it's 180 or so.

The insblock doesn't require any sand or fire clay to set the bricks on as it's very flat. I don't know about the other choices. Here's a couple of pics of the stuff.

[brickie in oz]

Re: Floor modification

your oven would be extremely well insulated.

If the oven itself is sitting on the concrete slab you will still lose mega amounts of heat into the slab no matter how you insulate.

[WJW]

Re: Floor modification

That's a good point Al.

I wasn't thinking it threough...if they rip up the floor and insulate, the walls and back will still be sitting on the slab...although his hearth brick wont be. Better than having the hearth sitting on the slab...but still not really isolated so that heat can't go into the stand.

Better than where she is now, but certaily not optimum.

Bill

[ShannonCorum]

Re: Floor modification

I imagine that some insulation as opposed to no insulation is better than where I am now. I'm not looking to have my oven hot for days on end. I want nice crisp pizzas, maybe a loaf or two of bread, and a roast or something. There will likely be times that all I cook are pizzas and nothing else. I wish I had more time to do more with it, but I don't. The whole purpose of building it to begin with was to get the same brick oven pizzas we had in St. Lucia. I'm afraid I have too many "toys" and not enough time to play with them all. If I can improve my pizza turnout, I will be happy. One day, when I have more time, I will demolish the whole thing and build it better.

Thanks for all the help. I'll be sure to keep everyone posted on how this turns out.

Shannon