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mrgweeto 08-02-2009 04:13 PM

We are getting close to finishing the dome. I have been reading about the curing process. I understand that it is crucial that you slowly eliminate mositure
by a succession of slow fires increasing the temp over a period of time. Heat turns the water to steam and if done too fast the only result will be bursting through mortar joints and brick. Now I have read first cure then render. We are going to put 1.5" to 2" of Heat Stop over the dome, put up walls and pour 6" of vermiculite inside. Now when one says render do you mean the Heat Stop layer over the dome? I would think that you want to cure after this layer and before the addition of the vermiculite. If not it would take forever to cure. The vermiculite out of the bag is dry. I'm coachable.

dmun 08-02-2009 06:06 PM

Re: Curing

We are going to put 1.5" to 2" of Heat Stop over the dome, put up walls and pour 6" of vermiculite inside. Now when one says render do you mean the Heat Stop layer over the dome?
This layer of additional thermal mass is quite optional. It will take longer to heat up and cool down, and of course be more masonry to cure. "Render" is the UK/Aus expression for what we call stucco, and most often refers to the coat over the insulation in igloo finished ovens.

Now as far as insulate before or after: I'm in favor of insulation before curing fires, here's why: I think most of the cracking problems come from temperature differential between the hot inside and the cool outside, and having insulation makes for less thermal shock. That said, lots of people cure before insulation, it's a matter of choice.

MK1 08-02-2009 07:18 PM

Re: Curing
The render referred to is the brown coat, scratch coat and final stucco layer on an igloo style build. You have a gable style enclosure with loose vermiculite. Go ahead and cure. The vapor will escape into the insulation but will dry out with the heat of curing.


ThisOldGarageNJ 08-03-2009 04:13 AM

Re: Curing
I finished my oven, the vermicrete over the dome, I waited ten days had my 7 curing fires and then started cooking. I used surface bonding cement(rather than stucco, adding acrylic fortifier and color after about a month. The surface bonding cement worked great and was easy to use and according to Quickrete is waterproof (the acrylic makes it waterproof)and will withstand the minor exterior heat. I also used the suface bonding cement on the block foundation. Much easier to use than mortar.

Are you insulating your oven ? or are you planning on using the heat stop as insulation ? that stuff is EXPENSIVE. I put whatever I had leftover on the dome after I was done laying for the day, a thin coat...

Good luck and enjoy

mrgweeto 08-03-2009 08:58 AM

Re: Curing
Thanks for all the responses.
To Mark's question:
The Heat Stop is $50.00 per 50lb bag and we are going to get one bag just to slather it on the outside of the dome. We have allowed for 6" of vermiculite which we feel is more than enough. A lot cheaper than the blanket. We are looking forward to doing the finish work and are forcing ourselves to be patient.

Neil2 08-03-2009 01:12 PM

Re: Curing
I insulated with 5 inches of 12:1 vermiculete then two layers of acrylic stucco - finished off the vent, chimney and everything before starting the curing firings.

My insulation shell is vented through the acrylic stucco with 1 inch vents at four places on the bottom and once at the top.

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