Super Isol Question

[DaveHI]

Re: Super Isol Question

2.6 MPa is about 400 PSI if I did the conversion right. A 36 ID torus 4.5 inches wide would have an area of about 550 in2. So 400 X 550 gives me 200,000 lbs. 200 fire brick weigh 1600 lbs.... I think you have a safety factor!

( I had the same worry so this motivated me to do the math)

[carioca]

Re: Super Isol Question

Hello Paul,

yes, the idea was to provide a sort of a key way for the perlcrete coming down the sides of the dome to meet the hearth slab, continuing the insulation down to the level of the calcium silicate board/s and providing a point of anchorage against sideways slippage of the dome body...

I've since poured the hearth slab without any 'well' nor embedded calcium silicate boards and will reconsider my options when I dismantle the forms next Tuesday.

In the meantime I've posted a question regarding the compressive strength of the CalSil, which according to some table quoted on the forum is a mere 2.6 MPa - just about one-tenth of that of quality concrete (25 MPa). Checking today for any answers, I noted you had the same concern a while back and were reassured by some answers you had received. I am STILL worried :-)

Have a beaut day!

Luis a.k.a. Carioca

[Hendo]

Re: Super Isol Question

Luis,

Sorry - I missed this post along the way somehow.

Thanks for the sketch, but I'm still not sure what you're trying to achieve with the well, that couldn't be achieved by simply piling up the perlcrete around the base of the dome, and having a uniform 5" slab.

Am I missing something? Or is the function of the well purely to provide a 'key' for the perlcrete, to prevent any possibility of outwards movement of the dome on heating? If so, is it wise to do this? From what I recall reading, other members seem to advocate allowing for some lateral slippage for things to freely expand & contract - eg the floor within the dome.

Paul.

[carioca]

Re: Super Isol Question

Hello Paul,

here's a rough sketch of the "well" idea - ignore the label 'Perlcrete': this should be the first layer of 25 mm CalSil boards embedded in the concrete...

The perlcrete would only be used to cover the dome, once the ceramic blanket is in place, and it would extend into the 'well' to further insulate the rim of the oven and give it some lateral support.

Do you think this might work out? Or am I weakening the slab too much in the central area?

Cheers,

Luis

[carioca]

Re: Super Isol Question

Hello Hendo,

yes, I could try the Fortecon moisture barrier UNDER the CalSil boards - I'll see how that works. If not, I can always rip it out while the concrete is still 'green'...

I'll do a sketch tomorrow to clarify what I mean re the 'well' (I'd have to switch on another machine to which my graphics tablet is attached).

Today I went into town to get 4 more bags of concrete. That means I have a total of 11 - and I only used 8 or so for the footing slab :-)

Cheers,

Luis

[Hendo]

Re: Super Isol Question

I've been mulling over this question of CalSil also as I approach the hearth pour, and my thinking was to put one layer of the board right down on the wet concrete and make it level. I'd put Fortecon over the entire surface of the hearth while it cures, so that should compensate for the moisture-sucking, if any, of the calcium silicate.

Just a thought ? what about putting down the Fortecon first, then the layer of CalSil, which might still get the concrete nice and flat without any potential curing problems due to dehydration?

My plan is to build the dome on this second layer, then make a narrow well around the perimeter of the dome so that once it has been smoothed with Densecrete and wrapped in a ceramic fibre blanket, I can pour vermiculite/concrete mix into this well for further insulation, then 'render' some 50 mm (2in) of the same mix onto the dome around the blanket. As a last coat, I'd use cement render to weather-proof the dome.

There's some fuzzy thinking yet about how to handle the interface between the 'well' and the remainder of the slab - perhaps self-levelling concrete?

I can?t quite picture what you?re proposing here re the well ? any chance of a sketch? Where is the well? In the CalSil layer?

Paul.

[CanuckJim]

Re: Super Isol Question

James,

Here's a link for gas burners I found a while back: Charles A. Hones. The range seems pretty good for many industrial applications.

Jim

[carioca]

Re: Super Isol Question

Ciao Hendo,

I've been mulling over this question of CalSil also as I approach the hearth pour, and my thinking was to put one layer of the board right down on the wet concrete and make it level. I'd put Fortecon over the entire surface of the hearth while it cures, so that should compensate for the moisture-sucking, if any, of the calcium silicate.

Then I'd put a second layer (my boards are only 25 mm - 1 in - thick) at right angles across this flat surface once the slab has cured.

My plan is to build the dome on this second layer, then make a narrow well around the perimeter of the dome so that once it has been smoothed with Densecrete and wrapped in a ceramic fibre blanket, I can pour vermiculite/concrete mix into this well for further insulation, then 'render' some 50 mm (2in) of the same mix onto the dome around the blanket. As a last coat, I'd use cement render to weather-proof the dome.

There's some fuzzy thinking yet about how to handle the interface between the 'well' and the remainder of the slab - perhaps self-levelling concrete?

Am open to suggestions and advice, as always...

Cheers,

Carioca

[Hendo]

Re: Super Isol Question

Yep, I'm going with 2" Calcium Silicate boards under the cooking floor, and a thin layer of sand (or sand/fireclay) just to level the floor tiles, if necessary.

[dmun]

Re: Super Isol Question

Paul,

Sand is a poor insulator. Only if you have no other choice should it substitute for vermiculite concrete or refractory insulation board. Unless you want to waste time and fuel, use the best insulator you can find.

[james]

Re: Super Isol Question

Hey Paul,
This all makes perfect sense. Of course we know those guys, and share information all the time. (I thought I recognized that oven!)

I'm not sure what they are doing for a burner, but I will ask.

My view is that the "bed of sand" technique is old fashioned, and has some drawbacks. It does not perform as well thermally, and sand can get wet and wick a lot of water (which I have seen happen more than once). Using enough sand, or sand and clay, to get your floor level and smooth is all you need as long as you are doing a good insulating layer under the floor. A number of producers switched their plans away from sand serveral years ago, and a handful still recommend you do it that way (which isn't good).

I think the oven in the photo is commercial and indoors, where it might not be as important.

This all makes sense. Thanks.
James

[Hendo]

Re: Super Isol Question

James,

Photo's were provided by a commercial installer, who coincidentally imports ALFA Caminetti ovens from Italy.

Correct me, but could the surrounding bricks be insulating firebricks? I've never seen anything like them, but the sand base for the floor appears to be the same height.

The company also markets a gas kit, which was the main reason for my contact, but it also sent me a series of photo's showing a very ritzy oven construction at a ranch somewhere in New South Wales. (BTW, the gas kit is way over the top and very expensive, and importantly one can't use any other fuel, so I've passed on that one!)

Anyway, this company and others I've approached here about off-the-shelf ovens quite often recommend that the floor be installed on a bed of sand, rather than other insulating materials like vermiculite concrete or Cal Sil board.

Cheers, Paul.

[james]

Re: Super Isol Question

Hey Paul,
Quick question. How thick is your sand bed?
James

[Hendo]

Re: Super Isol Question

I think play sand would work fine as a leveling medium.

Thanks for this David. The use of sand between the insulation layer and the floor does seem to be quite common here, at least in the commercial arena ? see pics below.

I'm using insblok 19 and it's kinda brittle/fragile... I would think even if you glued it, under pressure it would probably just break away anyway...

My Cal Sil boards are quite fragile too, and I?m hoping that the heat resistant adhesive will fill some of the (< ⅛?) voids between the slab and the underside of the insulation boards to give as much support as possible over the entire area. This was the main reason I decided to glue them down, after first filling up any low spots in the slab as much as possible.

After several attempts to get the SuperIsol board wet enough to allow me to spread some Refrax mortar [unsuccessfully, I might add], I can to the realization that the components of my Casa 110 were of such weight that they were not going anywhere. As I had leveled the base structure, I was not concerned about the floor being level.

Another tick for sand, or some sort of dry-mix product! I will, however, try placing a ring of refractory mortar around the outside bottom edge of the first dome course to seal the oven, as a number of people have recommended. I?ll let you know how I get on.

Thanks, Paul.

[james]

Re: Super Isol Question

I talked with the producer of SuperIsol early on, and they seemed confident that it would not go mushy and would just dry out. I got a sample very wet, and it held up OK.

I am going to ask them what they think about setting it in wet concrete. It could be a time saver, but I think it is worth asking them if they think that is a good idea.

If you have a cured slab that isn't entirely level, you can get your SuperIsol as level and smooth as you can, then use your under floor sand/clay layer to set your floor perfectly smooth.

I will also ask if the small amount of moisture in the fireclay/sand mixture would cause a problem. I can't image that it would, but it's worth asking.

For everyone setting their floor on either a thin bed of sand, or sand/fireclay, I think the comment that "gravity is on your side" is a good one. My Scott ovens have the floor set in the sand/clay mixture and they are not moving.
James