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Old 06-08-2014, 10:13 AM
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Default Oven cast in sections - cure before mortaring?

Hi folks,

I've cast my dome in 4 sections and it's been drying nicely for the past number of days in the sun. Having cast it in sections, I was able to expose the internal surface of the dome to the sun to help drying. I've used a ciment/fondu/grog/sand mixture for my casting. I cut up some polypropylene rope and added it to the mixture to serve as burnout fibres.

It has a 26" interior diameter and wall thickness of 2.5 - 3".

My question is this - should I light some or all of the curing/drying out fires before I mortar the sections together and before I add the insulation layers? It seems to me that it would be good to light at least some fires before mortarting the sections together as this would allow any moisture to escape more easily and reduce the risk of cracking?
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Old 06-08-2014, 08:43 PM
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Default Re: Oven cast in sections - cure before mortaring?

G'day
Cant see any problems mortaring it together? why would you not?
If you using Pearle-crete as insulation you introducing moisture back in the build and your back to square one with the drying

Regards Dave
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Old 06-09-2014, 01:44 AM
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Default Re: Oven cast in sections - cure before mortaring?

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Originally Posted by cobblerdave View Post
G'day
Cant see any problems mortaring it together? why would you not?
If you using Pearle-crete as insulation you introducing moisture back in the build and your back to square one with the drying

Regards Dave
Thanks Dave,

I thought the point of the burn-out fibres and going very slowly with the fires is that the difficult bit was getting the moisture out of the cast dome itself and giving it some time before mortaring it would allow some of this moisture to escape more easily. But it doesn't sound like it's much of an issue.

In any case, the dome has had a week in the sun already so I guess it's time to mortar :-)
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Old 06-09-2014, 03:32 AM
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Default Re: Oven cast in sections - cure before mortaring?

G'day
You still have not said what insulation your using?
If you use pearlcrete / v-Crete even over dry insulation it's still going to introduce water back into the structure. Its simple. The wet migrates to the dry.
You can't change that. You can slow it down 1 inch of V-Crete at a time a week between each coat . Let the sun and the wind do it for you. Then a low and slow burn you don't have to crack your oven!
Regards dave
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Old 06-09-2014, 05:51 AM
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Default Re: Oven cast in sections - cure before mortaring?

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Originally Posted by cobblerdave View Post
G'day
You still have not said what insulation your using?
If you use pearlcrete / v-Crete even over dry insulation it's still going to introduce water back into the structure. Its simple. The wet migrates to the dry.
You can't change that. You can slow it down 1 inch of V-Crete at a time a week between each coat . Let the sun and the wind do it for you. Then a low and slow burn you don't have to crack your oven!
Regards dave
Ah sorry - I'm using 1" of ceramic blanket, then chicken wire and a layer of vermicrete over that.

Edit: I've just mortared the sections together. I've mortared generously over and around the joints. The Panyol 66 instructions say to mortar all around... do I need to do this? And if so, why is it necessary?
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Old 06-10-2014, 01:26 AM
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Default Re: Oven cast in sections - cure before mortaring?

It's to hold the thing together a bit more and fill in any gaps that heat can escape from.
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Old 06-10-2014, 02:36 AM
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Default Re: Oven cast in sections - cure before mortaring?

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It's to hold the thing together a bit more and fill in any gaps that heat can escape from.
Thanks David. She's all mortared up now. I'll let it dry for a few days and then put on the blanket and vermicrete outer layer.
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Old 06-10-2014, 04:58 AM
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Default Re: Oven cast in sections - cure before mortaring?

Yes, I'm assuming you are doing an igloo in which case I think the best procedure, or at least that's the way I've found it best, is to insulate with blanket, then the vermicrete in layers of about 32 mm (inch and a half) and let each layer dry for a week, two should be plenty to get a nice even form. Then do some drying out fires (i don't like the term "curing" as it gets confusing with curing concrete or refractory when you are doing the opposite and trying to hold the moisture in).Then finally do your outer rendered shell. If you are doing a dog kennel style then you don't need to add wet vermicrete you can just fill the space with loose/dry perlite, vermiculite or fibreglass ceiling insulation.
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Old 06-10-2014, 05:13 AM
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Default Re: Oven cast in sections - cure before mortaring?

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Yes, I'm assuming you are doing an igloo in which case I think the best procedure, or at least that's the way I've found it best, is to insulate with blanket, then the vermicrete in layers of about 32 mm (inch and a half) and let each layer dry for a week, two should be plenty to get a nice even form. Then do some drying out fires (i don't like the term "curing" as it gets confusing with curing concrete or refractory when you are doing the opposite and trying to hold the moisture in).Then finally do your outer rendered shell. If you are doing a dog kennel style then you don't need to add wet vermicrete you can just fill the space with loose/dry perlite, vermiculite or fibreglass ceiling insulation.
Thanks Dave - appreciate that.

Thinking a little ahead, what mix do people generally use for the outer render?
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