Super Isol Question

[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.

[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

[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

[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,

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

[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)