CalSil board and the oven wall

[ihughes]

I came across these plans for a barrel vault on an Oz website. They used calsil boards for the floor but the soldier coarse is sitting on the structural hearth. Pizza oven - Better Homes and Gardens
(You can download a pdf if interested, it's too big to attach here)

I had decided not to use Calsil in my igloo beacuse I thought water proofing might be an issue. But with the various vermiculite and render layers is this a concern as long as it is properly sealed around the base? Any helpful thoughts greatly appreciated.

And with the soldier coarse on the structural floor with no insulation wouldn't the heat leech away?

Also, these plans use a 300x300 refractory tile which looks about half the depth of a full brick. I'm going with the full brick herringbone anyway but is thermal mass a problem with this size of tile?

This is the website for the suppliers on the plan although it's a little short on detail and I'm waiting on specs.
Field Furnace Refractories

I'm no expert but this barrel vault design is a bit undercooked, if you'll excuse the bad play in words.

[Hendo]

Re: CalSil board and the oven wall

Ian,

I'm not sure that there is a 'correct' answer to the question of siting the dome directly on the hearth slab. To me it seems entirely reasonable to insulate under the dome, as well as the floor, but my firebrick supplier was quite surprised when I told him I was planning to do this. He indicated it was more common (in his experience) to have the Cal Sil sheets under the cooking floor only. But 'more common' doesn't necessarily mean 'better' IMO!

My rationale was similar to yours - that without insulation under the dome, there would likely be some leaching of heat down into the slab, so why not insulate between the two?

As to using Cal Sil sheets, I think as long as the stucco coats are sound, and you pay attention to the join at the base of the dome and hearth slab, moisture absorption into the Cal Sil from outside the dome shouldn't be a problem. (I'm assuming that the Cal Sil would not extend beyond the dome.)

Initially, I was going to lay my floor bricks on edge, but opted for brick-on-flat after considering other members' advice, especially with regard to minimising heat-up time. And a herring-bone pattern seems to be very popular, for practical reasons as well as aesthetics.

Cheers, Paul.

[ihughes]

Re: CalSil board and the oven wall

Thanks Paul, our thinking is the same.

I heard back from the refractory supplier and it looks like they're now suggesting using insulation brick (I.F.B) rather than Cal Sil sheets. I've got a question with them about the pros and cons.

Anyone got any ideas?

The prices look a bit cheaper than what you guys in Adelaide have been paying. Fire Brick at $2.70 each. The same company also supply oven doors, peels and stainless steel pipe and hat for the flue. Naturally I'd rather go Forno Bravo but shipping costs do add up when being sent to Australia ...

cheers
ian

[dmun]

Re: CalSil board and the oven wall

Insulating firebrick is similar to vermiculite concrete in it's insulation value. You had better plan on two layers of them if you are going that route. They are cheaper, but it's not really what they are designed for, which is to withstand the red-hot heat of ceramic kilns, which you don't need.

[ihughes]

Re: CalSil board and the oven wall

Thanks for the info dmun. Being a novice in such areas any detail like that makes it easier to talk with the suppliers.

The insulation bricks are 230x115x75. What is the reasoning behind two layers?

cheers
Ian

[dmun]

Re: CalSil board and the oven wall

The insulation bricks are 230x115x75. What is the reasoning behind two layers?

Just to get enough insulation, so your oven gets up to pizza temperatures without burning whole forests. 75mm is almost three inches, as compared to the recommended 4, so a double layer may be overkill. 115 is four-and-a-half. Maybe a single layer on edge would do it.

This is just an off-the-cuff guess, I'm sure you could get a material data sheet from the supplier, and check the "r" ratings.

Can you get Aerated autoclaved concrete (aac) blocks in Austraila? A layer of that might be more affordable.

Here's a previous discussion on that topic:

http://www.fornobravo.com/forum/f8/a...ght=autoclaved

[carioca]

Re: CalSil board and the oven wall

<SNIP>

Anyone got any ideas?

The prices look a bit cheaper than what you guys in Adelaide have been paying. Fire Brick at $2.70 each. The same company also supply oven doors, peels and stainless steel pipe and hat for the flue. Naturally I'd rather go Forno Bravo but shipping costs do add up when being sent to Australia ...

cheers
ian

Ian and others Ozzies,

pls find attached a snap of my progress a month ago which shows in particular the insulation aspect.

I had about 50 mm (2in) of perlcrete under the planned hearth, then mortared (high-temp mortar) 230x115x75mm insulating firebricks ($A3.30 ea. - lots cheaper than Hebel AAC btw) in a 1 m dia. circle.

Inside this circle is another layer of perlcrete (about 50 mm), plus TWO lots of different types of Calsil sheets cut to fit - bearing in mind Maver's exortation that 'you can't have too much insulation'.

I mortared a ring of straight full-size firebricks to the insulating firebricks. The chains of halved, tapered dome firebricks from Darleys in Melbourne are stacked dry in the picture so I could get the configuration right...

The IFBs and high-temperature mortar ($A27/bag of 20 kg) as well as a second roll of ceramic fibre blanket 25 mm x 600 mm x 7600 mm I collected from Field Furnace Refractories in Sydney - their man Andrew is extremely helpful with any questions.

And because they gave me such a good deal, I also collected a 200 mm (8in) dia. stainless steel flue with top, a round stainless steel peel and a S/S coal rake...

FFR have been pushing the Better Gnomes than Gardens (my moniker for a mag I once worked for) barrel oven and the suitable tapered bricks, incidentally. Andrew also suggested the insulating firebrick first chain - AROUND the CalSil and the hearth bricks.

So the dome now rests on more or less solid foundations. I cut the hearth tiles (50 mm thick and 300 mm square) to fit inside the dome walls and resting on all the insulation.

Andrew also suggested I adapt a full door arch and separate flue arch from the BH&G design to my dome, and sold me the requisite 75->51 mm tapered bricks ($A2.8 0 and $A4.30 ea, respectively - the flue arch bricks are 345 mm long).

I've since built both arches, but if I had to do itagain, I would put some CalSil insulation boards BETWEEN the twin arches, to prevent heat leaching from one to the other and out...

If you'd like to see more snaps of my very slow progress, I could point you to my picasaweb album for Forno del Gallo chi canta.

Cheers,

LMH

[Hendo]

Re: CalSil board and the oven wall

On the Field Furnace Refractories website at Field Furnace Refractories, I notice in the photo that they have panels of what I assume is 42% alumina brick measuring 690mm x 460mm x 76mm. It may be worth considering these as an alternative to standard bricks for your floor, providing you don't need a crane to shift them! Let's see - each panel is the equivalent of 3 bricks wide x 4 bricks high = 12 bricks @ 4kg = 48kg. More than I could handle on my own. Cutting a circular edge would also be a bit of a challenge - I wonder if the company would do this? Anyway, food for thought (and probably not much else!).

Cheers, Paul.

[dmun]

Re: CalSil board and the oven wall

I thought about these panels, which are called refractory tiles in this country, and sold by HW. It turns out that they are WAY more expensive than brick, as well as being hard to handle.

[ihughes]

Re: CalSil board and the oven wall

SO the "r" factor here is probably the clincher.
Carioca you have a lot of insulation. The pompei plans call for a sheet of Superisol which appears the same as CalSil board and your build has gone Maver's "too much is never enough" route which I fully applaud.

But for us mere mortals I was thinking of just using the Calsil. When I talk to my new friends at Field Furnace what is the "R" factor I need to look for an ideal since there are obviously several alternatives?

cheers
Ian