Old 11-15-2006, 10:24 AM
Join Date: Apr 2005
Location: Brazil
Posts: 306
Default Vermiculite cement mixing


In some of my old answers I had explained how to work with vermiculite/cement mixture and percents between them.

If is your intention to use the vermiculite/cement to isolate your dome, your could go as high as 8:1, that is better as isolation.

To do the mix, it will better to mix the vermiculite with the cement when dry, this permit each particle of vermiculite to be surrounded by cement before be wet.

Whit the mixture perfectly homogeneous could be better to shower it with a light stream (more a smooth shower) and mixing at same time, to not “wash” the cement from the vermiculite particles.

Good work.

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Old 11-20-2006, 05:02 AM
Join Date: Nov 2006
Posts: 6

hello all,

Yet another novice question that needs proffesional answering...

Is it possible to use high temp mortor paste,(the one to bond firebricks with) and cast it into a mold instead of refractory concrete?

I plan on making my molds throughout the winter in my heated garage so it will have time to cure. I'm still stuck on the dome mold technology.

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Old 11-20-2006, 05:15 AM
dmun's Avatar
Join Date: Jul 2005
Location: New Jersey USA
Posts: 4,216

Originally Posted by asparapani
Yet another novice question that needs proffesional answering...
You're right on this - You need a professional answer. Refractory mortar is not made be any wider than a brick joint. There are castable refractory materials that harden at room temperature, but other than a flue transition, no one here has much used them.

You need to talk to a refractory dealer. These places sell to people building serious things like kilns and boilers, and will have access to an applications engineer, who will be able to answer your questions. Refractory materials, even fireplace mortar, is expensive stuff, far more expensive than firebrick, and you don't want to cast up a big dome sector, and find that it's cracking on drying or firing.
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Old 11-21-2006, 04:51 AM
Join Date: Nov 2006
Posts: 6

thanks for the profffesional suggestion....

I'll go speak to a refractory specialist
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Old 12-11-2008, 04:27 PM
Join Date: Sep 2008
Location: australia
Posts: 29
Default Re: Hearth and Dome construction questions

Hmmm. I am working on the dome, and have done 4 courses, and it looks as if the 5th will be the last that can be done without some sort of formwork. I have used old common red bricks, which vary in size quite a lot, firebricks too expensive around here. ($7 each). Have used mortar only, no shims, to place the bricks, and so far it has worked OK. Using formwork will be a pain, and I have been considering making a precast refractory concrete dome section to finish the dome off, rather than laying more bricks.

Sounds as if this is not really possible - too hard to get a mix of concrete which will stand the heat and which will set at air temperature.

Filling a perfectly good dome with sand to make a sand form seems like a desperate measure. Any other ideas?
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Old 12-11-2008, 05:00 PM
egalecki's Avatar
Il Pizzaiolo
Join Date: Mar 2008
Location: Virginia
Posts: 1,049
Default Re: Hearth and Dome construction questions

I built mine without forms. Use something to prop up the brick- it shouldn't take more than a couple of minutes to set up enough to remove it. A stick would do, really. I used bamboo sticks (1/4 inch or so in diameter) for mine.

You can do the sand, but it's messy and you can't clean up the joints on the inside. Fighting gravity is possible, just be creative.

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Old 12-11-2008, 05:05 PM
Join Date: Sep 2008
Location: australia
Posts: 29
Default Re: Hearth and Dome construction questions

Sticks - yes - good idea. It will only be for a couple more courses then I can build a small round platform to support the last couple of really small courses near the centre. Thanks. And maybe I'll use a bit more lime to make the mortar stickier as well.
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