#11  
Old 07-16-2011, 07:25 PM
Peasant
 
Join Date: Apr 2011
Location: San Diego
Posts: 37
Default Re: Perlite/Mizzou castable

Posting some pictures, so you don't have to click on the facebook page!

Tomorrow is DOME DAY !!!
Attached Thumbnails
Perlite/Mizzou castable-261827_10150264997130559_630930558_7639814_3261656_n.jpg   Perlite/Mizzou castable-266359_10150265010310559_630930558_7639876_5133440_o.jpg   Perlite/Mizzou castable-265439_10150265010405559_630930558_7639878_6555284_o.jpg   Perlite/Mizzou castable-266307_10150265031780559_630930558_7640014_7648646_o.jpg  
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  #12  
Old 07-16-2011, 07:37 PM
Serf
 
Join Date: Sep 2010
Location: Western MA
Posts: 20
Default Re: Perlite/Mizzou castable

Hi again,
Are you still planning to mix perlite with the mizzou?
I covered my mold with shrinkable mylar( used for covering windows) to guarantee a good release. I still had to yank pretty hard to get it out.
Rich

Last edited by tinkerric; 07-18-2011 at 04:01 AM.
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  #13  
Old 07-16-2011, 07:48 PM
Peasant
 
Join Date: Apr 2011
Location: San Diego
Posts: 37
Default Re: Perlite/Mizzou castable

I think I will go with a 1:1 mix. I really hope that won't make it too fragile, but 22" is not too large. And pizzahacker does that! LOL

how is your kettle-bbq-refractory-cement-walls-dome working ??
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  #14  
Old 07-17-2011, 05:52 AM
Serf
 
Join Date: Sep 2010
Location: Western MA
Posts: 20
Default Re: Perlite/Mizzou castable

I haven't fired my oven up since insulating the dome. It did pretty well with pizza before insulation, so I expect it to heat up faster and stay at temp more easily.

I have a few questions for you. Is your supporting slab insulated or just straight concrete? What is going to support the brick "arch" entrance?
Was your stand an existing table frame or did you make it? It all looks nice and think it will work fine.

As you said that you plan on insulating your oven, you could just cast your dome from straight mizzou and maybe a little thinner than 2". If you have a 55lb. bag,there should be enough material for 1 1/2". Though you should do the calculations so you don't run short.

From the pictures I've seen, it looks like Pizza Hacker may be using a commercial lightweight castable refractory, something much less dense than I made. The pictures of his early "oven" had what looked like firebrick walls and a lightweight dome sitting on top of them, very similar to what you have set up, but you've probably seen those pics as well.
I've seen recipes for a lightweight reftactory using premixed Rutland refractory cement mixed with perlite. I wonder if this is how pizzahacker did his first dome?

Silly as it may sound, one of the reasons I was cutting my dense castable was to add volume, so I could cast the dome with just one 55lb bag of ks4.
Having never worked with the material and never made a cast from a mold, I didn't want to possibly waste expensive material.

It has dawned on me that the perlite mixed in the dense castable, may actually be slowing down the dome's heat absorbtion, interfering with the heat transfer between all the particles of dense castable.
Well it seems to be working.

Enough ramblings for now. Hope your cast goes well.
Rich

Last edited by tinkerric; 07-17-2011 at 08:55 PM. Reason: misspell
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  #15  
Old 07-17-2011, 10:12 AM
Peasant
 
Join Date: Apr 2011
Location: San Diego
Posts: 37
Default Re: Perlite/Mizzou castable

Rich,

thanks for your comments!

the supporting slab is 1 50lb general cement and probably 1:2.5 perlite.. I added too much water to the cement and I had to add perlite and perlite and perlite until I got the desired consistency.. Is that considered some kind of insulation?

About the little arch, I am not sure. I was thinking of filling the joint with mortar and trying to put it in place once it settles and add more mortar on the wall bricks. Or I'll find a better solution

The frame is a table that lost its glass top and it's incredibly strong!

For me too, one of the three reasons for adding perlite to the mix was to grow the overall volume, in addition to weight reduction and adding some insulation.

I really hope things will work!

What about a little chimney?
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  #16  
Old 07-17-2011, 01:53 PM
Journeyman
 
Join Date: May 2009
Location: Detroit
Posts: 398
Default Re: Perlite/Mizzou castable

I personally wouldn't add anything to a commercial refractory, but if you need to I think coarsely crushed firebrick would be your best economical easy to find bet. Perlite is the absolute last thing you would want to use, it is a great high temperature insulator which you are adding to an area of the oven that you want to conduct heat half way decent so it can first store heat, and eventually release it. Perlite is going to drastically reduce the conductivity of the oven dome.

You are so close to a small but totally functional oven I would really do what it needs to get there. Add a couple inches of 6:1 perlcrete on top of your structural hearth. Don't put the perlite in your dome, and finally insulate well over top of the oven. If you do that you will essentially have a miniature version of what this site is all about.
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  #17  
Old 07-17-2011, 02:09 PM
Serf
 
Join Date: Sep 2010
Location: Western MA
Posts: 20
Default Re: Perlite/Mizzou castable

Hi,
Your slab is a little bit insulated. I think a 3 to 4" thick perlcrete (6 to1) is what is generally used for hearth insulation.
You could cut your hearth bricks to the diameter of the oven and then cover it all with a 10 to 1 mix of perlcrete.
I used all of a 6 cubic foot bag of course agricultural perlite ($33) and a bit of an 80lb bag of portland cement ($10) to cast a 4" pad and cover the entire oven.
The perlcrete is fun and easy to work with.

I had planned to cast an arch with a chimney, but since this oven is experimental I made an entry out of a bit of copper flashing I had.
It worked well for 3 firings so I left it in place when I insulated.
The oven works fine without a chimney. It draws fine, though I wonder if it might burn a little cleaner with a chimney.

I'll attach some pictures so you can see what I'm talking about
Have Fun Rich
Attached Thumbnails
Perlite/Mizzou castable-dscn1615.jpg   Perlite/Mizzou castable-dscn1630.jpg   Perlite/Mizzou castable-williamsburg-20110611-00426.jpg   Perlite/Mizzou castable-dscn1626.jpg   Perlite/Mizzou castable-dscn1629.jpg  


Last edited by tinkerric; 07-17-2011 at 08:58 PM.
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  #18  
Old 07-18-2011, 09:54 PM
Peasant
 
Join Date: Apr 2011
Location: San Diego
Posts: 37
Default Re: Perlite/Mizzou castable

Dome Day part one just ended with a twist. Just a few minutes before starting the Mizzou with plans of setting that on top of the weber I decided it was a bad idea. Trying to pop the cement out and sitting it on top of the bricks may have called for troubles, so I decided to go with sand. I filled a couple of bags of packing_peanuts to save a few dozen pounds of sand, taped them to the cooking floor and covered with sand. Added more sand to shape the dome. The situation is now calm and solid.
My question is now simple: can I lay the cement on the sand or will it create problem as it's not water tight? Should I cover it with a thin plastic cover?

Peace!
Attached Thumbnails
Perlite/Mizzou castable-279036_10150268978225559_630930558_7679751_3109176_o.jpg   Perlite/Mizzou castable-265987_10150268978145559_630930558_7679749_1821097_o.jpg   Perlite/Mizzou castable-271720_10150268978195559_630930558_7679750_644680_o.jpg  
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  #19  
Old 07-19-2011, 04:31 AM
Serf
 
Join Date: Sep 2010
Location: Western MA
Posts: 20
Default Re: Perlite/Mizzou castable

Builders of clay/mud ovens usually put newspaper over the sand form. But..
I think with castable refractory you don't want water drawn out of the cement.
So maybe cover the form with cling wrap and then newspaper?
I'm just speculating , others here have cast over sand and might chime in.

As long as you are making a sand form, why don't you also cast the entrance arch at the same time?

Btw, I would have to agree with Shuboyje about just casting with straight Mizzou if you can handle the weight.
I think a thinner dome, insulated on the outside is the way to go. The perlite that I mixed with dense castable is just short circuiting heat transfer.
Using perlite came from my trying to reverse engineer Pizzahacker.
But as I said earlier, I don't think that he was adding perlite to dense castable, he has made something much less dense than even that.

Good luck and keep us posted
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  #20  
Old 07-19-2011, 09:41 AM
Peasant
 
Join Date: Apr 2011
Location: San Diego
Posts: 37
Default Re: Perlite/Mizzou castable

Great!

I will do a first layer of pure Mizzou and save the perite for the outer layer. Wrap and newspaper sound good. The two bricks at the entrance make me think it will be kind of stronger and less likely to get accidentally chipped.. They are also easier on the eyes!

Should the little chimney be in between the two entrance bricks?

Getting Ready!
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