Starting new 36" build

[brickie in oz]

Originally Posted by Neil2

Uneven support like this raises the concern of differential settlement.

A concrete pier/pile at the back would alleviate that problem and help carry the load, the slab could also be suspended off the soil via the pier/pile to help with the moisture issue that will arise.

Id be putting lots of waterproofer in the hearth slab too as moisture will travel into the slab from the retaining wall, it doesnt take much moisture to make an oven under perform.

[deejayoh]

Originally Posted by brickie in oz

A concrete pier/pile at the back would alleviate that problem and help carry the load, the slab could also be suspended off the soil via the pier/pile to help with the moisture issue that will arise.

I really don't want to suspend the slab if I can avoid it. I don't see how moisture can travel up through a waterproof barrier into a slab. But settling is a concern. The dirt behind the wall was backfilled after the wall went in, and looking at it this weekend I can see it has already compacted about an inch in the past few months. I was thinking I could pack it down really well - but maybe I should drop a couple sonotube forms in the corners? There is a clay layer down about 2-3 feet that you need a jackhammer to break up.

Id be putting lots of waterproofer in the hearth slab too as moisture will travel into the slab from the retaining wall, it doesnt take much moisture to make an oven under perform.

Not sure what you mean by waterproofer. Are there additives for the concrete, or do you just mean sealants?

on the moisture issue, I was thinking that since the retaining wall is a separate structure, and below the hearth - that moisture shouldn't be able to wick into the hearth if I hadthe protection on the bottom. But I'll be the first to say I have minimal knowledge of concrete!

TIA for the guidance

Dennis

[brickie in oz]

Originally Posted by deejayoh

maybe I should drop a couple sonotube forms in the corners?

That would stop any settlement issues for sure.

Originally Posted by deejayoh

Are there additives for the concrete,

Correct, add them at the mixing stage and the concrete wont wick any moisture.

Originally Posted by deejayoh

on the moisture issue, I was thinking that since the retaining wall is a separate structure, and below the hearth - that moisture shouldn't be able to wick into the hearth if I hadthe protection on the bottom. But I'll be the first to say I have minimal knowledge of concrete!

Ive seen moisture travel 6' up masonry over time, if you put a physical barrier in place it would help too.

Better to be safe than sorry, there have been a few tales of woe on the forum all due to moisture wicking, once it starts to wick after a build it would be almost impossible to stop without a pull down and restart.

Same goes for heat wicking, best to get it sorted out before the build.

[deejayoh]

Thanks Al - I also read your comments in the Insulation sticky thread

So, paying close attention here. I did some searching with the google and came up with Xypex, an additive that you incorporate in the mix that is supposed to prevent water wicking

Xypex Corporation

So I am thinking of using this (assuming I can find it!) along with a moisture barrier to have a hearth layer that is moisture impermeable.

On top of that, I'm thinking 3 inches of insulating board - local supplier doesn't say which this is but I will go with theirs or the FB board from our sponsor.

Seattle Pottery Supply E-Catalog: Insulating Board - BACKUP BOARD - 1900 Degree F. - 12 in x 36 in x 1 in - 16 Piece/Case

Think that will be sufficient?

[brickie in oz]

Originally Posted by deejayoh

So, paying close attention here. I did some searching with the google and came up with Xypex, an additive that you incorporate in the mix that is supposed to prevent water wicking

Xypex Corporation

So I am thinking of using this (assuming I can find it!) along with a moisture barrier to have a hearth layer that is moisture impermeable.

The spec sheet reads ok apart from only being able to buy larger than needed parcels of it.
You should ask a hardware store about it or equivalent stuff.

Originally Posted by deejayoh

On top of that, I'm thinking 3 inches of insulating board - local supplier doesn't say which this is but I will go with theirs or the FB board from our sponsor.

Seattle Pottery Supply E-Catalog: Insulating Board - BACKUP BOARD - 1900 Degree F. - 12 in x 36 in x 1 in - 16 Piece/Case

Think that will be sufficient?

3" of Calcium Silicate board may be overkill?
I have 40mm underneath my hearth and the oven stays hot for days and days.

[deejayoh]

Well, we are into February, but I am finally seeing some progress on my build.

Couple of changes from my initial post:

• I have decided to go with a 39" oven instead of a 36". almost went with a 42" but made a firewood vs. stairs tradeoff
• I decided to pour the lintel rather than use concrete block supported by angle irons. I figure the angle irons are going to rust over time and leave stains at best

So I got the stand built a couple of weeks ago, and today I hired a couple of guys from my friends construction crew to help me pour the lintel. Actually, I thought I would get the hearth poured too, but the &*!@ Salmon Bay Concrete store is closed on Saturday, so I could not pick up the Xypex AdMix C-1000 that I am putting in the hearth to make it waterproof.

Let me tell you, this stuff is super pricey. You mix it in at 2% of the weight of the concrete, and it's $6 per pound.... More than the concrete, but I figure safe is better than sorry.

I also have my ceramic blanket and duravent already on hand, so I am a bit ahead of the game there. Just need to get the bricks, mortar and FB board.

Finished Stand

Forms ready for hearth

Pouring the lintel

[deejayoh]

I have a question about insulation between the hearth layer and the cooking floor:

I purchased 2" of FB Board insulation to install under my oven. The spec sheet for the board says that:

"One 2" thick layer of FB Board panel reduces the 800ºF cooking floor of a pizza oven to roughly 170ºF at equilibrium"

I have seen recommendations for 2 layers (4") of the FB board on the board. That seems like total overkill to me - as the goal of the floor insulation should be to reduce the heat transfer to the point where it is equivalent to roughly the temperature of the hearth - about another 100-130 degrees

Beyond that point, you really aren't losing any heat so you are past the point of diminishing marginal returns from insulation

I am trying to figure out if there is a cheaper material I can use at 1" thickness to accomplish that last bit of temperature reduction. Something I can source locally that is more in the $5/sq foot price range than the $12 per sq foot that the FB board costs.

Any suggestions? Would an inch of perlite do the trick?

[GianniFocaccia]

1" of ceramic board is equal to 2" of vermicrete or perlcrete. I put in 3 1/2" of vermicrete (easy to mix and install) under 2" of board, which is becoming common. 1" of perlcrete isn't going to do much for you.

[deejayoh]

Originally Posted by GianniFocaccia

1" of ceramic board is equal to 2" of vermicrete or perlcrete. I put in 3 1/2" of vermicrete (easy to mix and install) under 2" of board, which is becoming common. 1" of perlcrete isn't going to do much for you.

Thanks Gianni
So it takes 3 1/2 inches of vermicrete to manage 170 degree temperature? Seems like a pretty inefficient insulator.

Due to height limitations I am looking for something no more than 1" thick

I saw this at our local pottery supply. This board looks like it might do the trick. Any thoughts?

[GianniFocaccia]

Can't tell, DJO. Maybe you can email them and ask for the board's R-Value and MSDS, which will tell you the board's composition. Since you'd be using it as backup instead of hot-face insulation, I'd be tempted to use it as long as it's compressive strength is acceptable.