Block Stand Question - Pompeii 42"

[Yeager]

Hey guys - any ideas?

[Gulf]

Hey All,
Making good progress on my block stand - filled the every other cores today on the block. Getting ready to form and pour the concrete and insulating pad next. What is the "latest" that everyone believes is the best way to insulate between the (3.5") concrete pad and the firebrick? Is it the vermiculite/perlite mixture or stone that can be purchased?

Also, since I am going to have a roof build around my dome, should I make it easy for myself and ensure that the surrounding ~4" is concrete so I can mount the steel studs to it?

thanks,
Yeager

I can't speak for what everybody believes. But, imo the best insulation is FB board (ceramic fiber board) or Calcium Silicate (CalSil). But, it really boils down to what you want to spend. The vermicrete or perlcrete is a good cost efficient alternative. I and several others have used a combination of the v/pcrete and the boards.

Definitely leave the concrete exposed to where you can anchor your plates directly to it. I would place a waterproof barrier between the concrete slab and the insulation to help prevent wicking. And, I like an idea by RandyJ . He placed concrete pavers on top of his concrete hearth that also elevates the insulation. That puts the insulation high and dry if water should get in. You can check that out here.

[Yeager]

Great idea. So it looks like I would need 2-3 boards for a 42" oven. I noticed Randy's picture had two boards stacked - any idea how much benefit it is to have two levels vs just one?

So for thickness:

Pizza Cooking surface - 2.5"
Forno bravo Insulation board - 2.0" (assuming I just have one level)
Bricks to provide elevated insulation board - 1" (maybe 1.5"?)
Concrete Pad - 3.5"

Total 8.5"

Is the FB insulation board unique or are there others on the market to consider?
If the Insulation board is elevated do you think a moisture barrier is still needed? (my gut says no - because moisture would then just trap versus fall down below - but not sure).

thanks,
Yeager

[Gulf]

It is very hard for me to say how much under floor insulation is needed, and where the law of diminishing return starts. 2" of board insulation is what is recommended. After that, it is what you can be comfortable with spending. I used 4" of vcrete and 2" of CalSil. Randy, and many others who did not want the trouble of working with the vcrete went with extra board insulation.

On the moisture barrier, I think that I would still place it directly on the hearth slab to prevent moisture from wicking up. That is just my opinion. It won't be a killer if you leave it out. And, it wont break the bank if you buy a piece of plastic to place there.

[DavidApp]

Hello Yeager

After much thought and discussion on this site I went with 3" of FB under my floor. I have built a previous oven with no under floor insulation and suffered the consequences.

I am very happy with the heat retention of my oven. 3" FB under the floor 3 1/2" blanket over the dome.

You can make your slab overhang the concrete blocks if you need a bit more room on your slab.

David

[DavidApp]

I placed some plastic on the hearth slab and folded it up the sides of the FB. Ended up using Vcrete under my vent support as I had run out of FB.

I cast blocks 3" thick.

David

[RandyJ]

Hey Yeager how are you. I had a height that I had in mind when I was starting. I don't remember the exact height but I think it it was 42.5 inches. That was the original reason that I did the patio blocks, but it also helps with drainage if it were to get wet. I wrapped mine in a tarp when I was not working on it. That worked out good for me. If you are going to do a enclosure then you want to leave at least 4 " maby a littlebit more. I ended up going with 18 gage studs to help with snow load. The framework was very stout and I am happy I went that route.

As for the insulation I did not want to do the vermicreete and I did not think that it was that much more money I did not think and it was faster and easier. I don't have a door yet but I normally have temps around 400 F 24 hours later. So I think I am happy with the way it performs.

Randy

[Yeager]

So I spoke with some guys at Armil CFS and think I am going to go with Super Isol. Couple questions:

1) Is Super Isol moisture sensitive also? (i.e. should I elevate). I think I am going to go with 2" thick Super Isol unless someone believes I should use two 2" or two 1.5". I believe it will take 4 of the 24x39" tiles to provide insulation board coverage.

2) If you want to have a level hearth with the pizza cooking surface, how do you avoid the firebrick from transferring heat to the concrete hearth? Do you need to airgap it, put in a special grout?

thanks,
Yeager

[Gulf]

Here is some reading for you on some past builds on this forum with Super Isol ? (Calcium Silicate). I would use at least 2" of the board unless it is placed on top of a few inches of v/pcrete. Some of the recent formulas for CalSil are a little more water resistant than that in some of the earlier boards. You will need to check the specifications of the particular insulation that you intend to use. The CalSil that I used did not have those additives. I took great pains to keep it dry. But, it will dry out if it does. I would elevate the insulation. I think that RandyJ 's idea will someday be the norm .

If you want to have a level hearth with the pizza cooking surface, how do you avoid the firebrick from transferring heat to the concrete hearth? Do you need to airgap it, put in a special grout?

Can you explain that question a little more?

[RandyJ]

I would say that how much insulation you use is a part of your buget it will cost a little more to buy the board insulation, but it is a lot easier to install and faster. That said I don't see many going much over 4" but 3" would work too.

You will want the entry at the same high as the floor. IT can be a little hard to picture it in your mind I poored a lip that stuck out the front to hold the vent and still had a few inches of cf board to finish the heat break.

Randy

[UtahBeehiver]

Yeager,

I elevated my CaSi insulation by placing FoamGlas insulation (which has thermal conductivity properties similar to CaSi) underneath which is water proof and would not absorb moisture. But there are lots of ways to skin the cat. As you know CaSi gets mushy when it gets wet.

[Yeager]

Hey Guys,
Sorry for delayed response - been traveling a lot for work. Getting ready to pour the "table top" on my stand. I am "planning on pouring a 4" slab with a 8" overhang using qwikcrete 5000 with a lot of re-bar reinforcement.

Is a 8" cantilever too much? I am not for sure if making it thicker (i.e 5" thick would be better for that cantilever profile). Attached is a CAD drawing of what I am planning. It is mainly for aesthetics.

Russell - that is one of the prettiest layouts I've ever seen!!

Couple questions that's been brewing!

Heatbreak - For the "heat break" doesn't the hot bricks eventually touch "some" of the concrete if it's truly a flush floor? Russel, is your heat break the piece of metal looking item? It has a bricks on outer left and right that still touch. I may be in left field here - sorry guys!

Dome - Been starting to think about building the dome. Only have another few weeks before it's regularly freezing temperatures, so may not be able to do much unless I tent the oven and have a heater! For making the dome and cutting the firebrick is there a saw that you recommend buying? For the first few rows I believe it's firebricks cut in half (4.5") with a slight angle on each side. Is there a predictable layout of firebrick size (they seem to get smaller as you approach the top) and angles of the brick? I thought maybe I could maybe rent a good saw and cut a bunch of the firebrick to have ready.

thanks,
Yeager

[UtahBeehiver]

In addition to the floor heating break I did a.semi heat break on the chimney arch by tapering the inner face so there was minimal surface contact with inner archer then stuffed gap with ceramic rope then high temperature caulk.

[RandyJ]

Hey Yeager for the saw I went with the harbor fright one with a rigid blade. That worked great for me and a lot of others as well. As for the over hang I would think you will be just fine, but a little thicker might look cool as well. My over hang is about 12" roughly and that lip is 6" thick. But if you cast it all as one pice I do not think you will have any trouble.

As for starting now I do not think you have a chance to finish before it freezes. Unless you have unlimited time at your disposal. I hit mine as hard as I could and it still took me more than a month to do, and I do not think we have that much time till it freezes. I do not know how long you want to keep it from freezing after you lay the bricks. Just because it is set it is not cured.

Randy

[Yeager]

Hey All,
Getting ready to start with my dome! (Winter is finally letting go!). Attached is my current set of plans. It is a 42" interior with The dome not sitting on the brick floor and a 4" thick of insulation board. Would love any comments or thoughts that you have. I am least comfortable with the opening/arch. I tried to set the flue on center right after the apex of the floor/door. And have a 1" lip for the door to rest against. Let me know your thoughts! (you won't hurt my feelings!)

thanks,
Yeager