#21  
Old 07-19-2011, 02:27 PM
david s's Avatar
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Default Re: Perlite/Mizzou castable

I found tearing the newspaper into strips and then wetting it, was then able to overlap them and have it conform to the shape of the compound curve without getting creases.
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  #22  
Old 07-19-2011, 04:46 PM
Serf
 
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Location: Western MA
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Default Re: Perlite/Mizzou castable

I think that now that you have a sand form it would be very simple to shape a nice entrance arch. You can get the door height, 63%, just right and then the oven is ready for insulation. With the brick entrance as pictured, it looks like you have a lot of fussing to do to get the height right and arch bricks to stay in place.
The sand form would also make it easy to include a chimney in the cast if you want one.
I was going to make an entrance with a chimney. but after firing the oven with the copper entrance arch I didn't find the smoke or heat to be a problem.
You won't be burning as much wood as the larger ovens.

The other suggestion I would make is to cut your hearth bricks to the diameter of the dome. This way, you have less to insulate and less hearth to heat.
Rich
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  #23  
Old 07-19-2011, 05:10 PM
Peasant
 
Join Date: Apr 2011
Location: San Diego
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Default Re: Perlite/Mizzou castable

Dome is up!

I will soon post some pictures... I am sure I messed things up, but so far everything seems to be okay... Not enough cement to cast the entrance arc, I'll have to stick to the bricks or live with the short pre-arc...

How can I determine the setting time before I cover all with a insulation layer? We're in SD and it's freaking hot these days, after two hours the surface is hard and dry already...
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  #24  
Old 07-19-2011, 05:51 PM
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Default Re: Perlite/Mizzou castable

I think you don't want it to dry too fast. I kept mine covered with plastic for a few days, it was also cooler here in May
How many pounds of Mizzou did you have.
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  #25  
Old 07-19-2011, 08:58 PM
Peasant
 
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Location: San Diego
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Exclamation Re: Perlite/Mizzou castable

This is much less attractive than the send dome!
Attached Thumbnails
Perlite/Mizzou castable-266710_10150269778965559_630930558_7686463_6532638_o.jpg   Perlite/Mizzou castable-271720_10150268978195559_630930558_7679750_644680_o.jpg  
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  #26  
Old 07-20-2011, 01:08 PM
Peasant
 
Join Date: Apr 2011
Location: San Diego
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Default Re: Perlite/Mizzou castable

Hello!

the dome is nice and hard as a rock this morning! The sand mold - although being hollow inside - held up the 60+lb well and did not move at all.

Of course I will not know if the structure will stay up when I remove the sand and I am a little bit concerned about that: I guess there is no way to find out if any part is too thin and ready to collapse. The instructions have a big warning about steam and explosion. As far as I understand the steam is produced both by air curing and fire curing, but especially with the second. Does this mean I need to do the fire curing, litte by little, before I pour the insulation layer?

I'm sure I can find all these answer in the forum, but my structure looks so atypical that I'd better be sure...

THANKS!
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  #27  
Old 07-20-2011, 02:13 PM
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Default Re: Perlite/Mizzou castable

If your castable contained fine fibres they are designed to burn away at low temp and leave minature pipes through which steam can escape, which assists the elimination of water. The castable does not need to be kept moist for days like normal concrete. It is a different chemical process and 24hrs covered after casting is all that's required. Your dome will not collapse, you can remove the sand. It will not hurt to wait at least a week to let the weather dry the casting for you. In fact the more sun and wind you can get on it the better because a moist casting is a bitch to get a fire going in.
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  #28  
Old 07-20-2011, 02:17 PM
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Default Re: Perlite/Mizzou castable

If you are using perlite or vermiculite mixed with water and cement as an insulating layer, you will also need to let this dry for a couple of weeks as it contains tons of water.
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  #29  
Old 07-20-2011, 02:35 PM
Peasant
 
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Location: San Diego
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Default Re: Perlite/Mizzou castable

thanks David! so should I burn the fibers with low fires and put the insulation (perlite, water, cement) only after that?
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  #30  
Old 07-20-2011, 05:20 PM
Serf
 
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Default Re: Perlite/Mizzou castable

I followed the curing schedule in the attached pdf.

I let my dome sit for a week before I started to cure it.

I insulated 9 days ago,4" of perlcrete, and left plastic on the dome for 5 days.
I fired the oven a few hours ago. The insulation really works. The surface temp of the dome didn't change as the inside heated up.
After about 45 minutes the dome began to steam. At this point the dome got a bit warmer, maybe 125 F.

The insulation is keeping the heat in the oven, but I imagine the water in the perlcrete is still robbing my dome of heat.

How long does it take to dry out 4" of perlcrete on the dome.

Here's my question for those with more experience, which is preferable, curing a cast dome before it is insulated with perlcrete or curing it after the perlcrete is put on?

Thanks Rich
Attached Files
File Type: pdf curing.pdf (142.3 KB, 196 views)

Last edited by tinkerric; 07-20-2011 at 05:42 PM.
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