#21  
Old 01-27-2008, 11:11 AM
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Default Re: baking expert seeks oven expert. MHGSOH!!

cheers everyone. got some great advice especially from cvduke. i did consider portland but was concerned about the lack of insulation, heat loss. portland with chicken mesh, great. i take it your oven was made upside down as you added extra layers inside.
if i use portland then can i add anything to it to make it more insulated? i know you cant mix in refractory. i would like to use bricks on the hearth but i have a good supply of second hand commercial oven tiles- phone any second hand bakery equipment dealer, they have loads. can put these under the bricks then have good deep hearth.
i am thinking of the aesthetics of the portland dome so want to cover it with something more "natural", clay, but cvdukes had special mix of portland fire clay powdered kaolin, would this make a good outer skin.
it seems the key to using portland is to have very long curing times, ie keeping it covered.
i am taking the bus to ireland and will probably experiment there.
just one sour note, my home the bus got vandalised last night-was staying with the girlfriend, they broke several windows but did not enter and steal damage anything- so it could have been much worse.

hey ho. summer will soon be here and i'll be baking sacred bread and loving every minute of it

blessings. michaelthebaker

HOME I S WHERE THE HEARTH IS
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  #22  
Old 01-27-2008, 09:11 PM
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Default Re: baking expert seeks oven expert. MHGSOH!!

Actally, I made the dome right-side up while sitting in my garage floor last february. It took less than a day to make the wire structure and pack the portland topping mix into it. But word of caution here... I hate to wear gloves when I'm doing anything cause I need the tactile feel to see if its going right. I always forget how caustic cement is and had alkaline burns on my fingertips for 2 weeks afterwards. My goal was to make the mortar a uniform thickness but it kept slumping down so around the bottom is thicker. Another problem I had is that I didn't make my dome big enough to really crawl into so it was a long reach to reach the back wall while I was packing the mortar. It would have been better if I had a helper to brace up the mortar from the inside while I was packing it from the outside. If you've ever worked ferro cement before, you know that you always have to work to a wet edge, so no stopping until its done.
After packing the mortar, it was covered with wet burlap and plastic for about a week in the garage. At the end of the week, I drug it outside and just left it sitting around uncovered over the summer. Didn't need to leave it that long, but so many other things to do. Ended up explaining to lots of people what the concrete doghouse was (cause it looked like those plastic dog igloos).
Come September, I started in earnest on construction for the oven base. Thats when I rolled the dome over to add more thermal mass to inside.... I just happened to have 100 pounds of stoneware clay left over from my pottery days. Attached pics show the inside of the dome as I was beating the clay into it. Look closely and you can see how rough the concrete was, plus a lot of uncovered hog-wire, also no uniform thickness. Figured the clay would add mass and could be made smooth inside so I would snag my skin reahing inside. It took about 1/2 day of clay work and smoothing A couple days of air drying and it alligatored pretty bad...major cracks all thoughout the clay but sincethe concrete was so rough inside, the clay adhered to the dome. I tried filling the cracks with more clay, but it was too tedious, so gave up and pulled out the fiberglass re-inforced cement. Followed that with the portlan/fireclay/kaolin.
Last pic shows the dome once it was manhandled up onto the hearth. It took 3 of us so I figure it was up to around 250 pounds. After it was in place, I poured 80 pounds of portland concrete onto it just to add more mass. I figure at that point, you can add mass as needed. My dome's inside a steel-stud framed roof ...filled with lots of vermiculite and covered with a vermiculite concrete roof.
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baking expert seeks oven expert. MHGSOH!!-dome-packing.jpg   baking expert seeks oven expert. MHGSOH!!-dome-packing-2.jpg   baking expert seeks oven expert. MHGSOH!!-dome-above.jpg  
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  #23  
Old 01-28-2008, 02:09 PM
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Default Re: baking expert seeks oven expert. MHGSOH!!

thanks again for all the info. i wont be getting round to build for a few weeks. will let you all know how the project goes. anyone have advice about adding vermiculite to portland cement- i thought you could only add it to refractory cement. need as much insulation to weight with strength as possible.
cheers
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  #24  
Old 01-28-2008, 03:23 PM
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Default Re: baking expert seeks oven expert. MHGSOH!!

5 parts verm/perlite to 1 part Portland.

If you look at these pages, they show me mixing up the bottom insulating layer.

http://www.fornobravo.com/forum/8/da...ss-2476-7.html (Dave's Pics of Progress)

Just add water till it all holds together, and you can just squeeze a bit out.

Do make sure to mix the cement and perlite or verm BEFORE adding the water.

I hope this helps....

Dave
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  #25  
Old 01-28-2008, 08:59 PM
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Default Re: baking expert seeks oven expert. MHGSOH!!

Just to add to Dave's vermiculite concrete advice:
I've been able to get by with an 8 part vermiculite to 1 part portland mix. See
http://palmettovermiculite.com/files...Aggregate2.doc for particulars on weights and strengths of various mixes.

I do the mixing in a 5 gallon bucket. First I add a few inches of water, than a measure of vermiculite from another bucket that I pre-marked with eight of my scoops (which is probably about 1.5 quarts)... than one scoop of the portland, followed by a second measure of vermic and than another scoop of portland. Than I use a handheld drill mortar mixer like you use for sheetrock mud to really stir things around. Especially important to move the mixer up and down through the mix. Then I pour in the rest of the water... once you do a batch or two, you'll figure out how much but basically it gets to be a runny oatmeal. Too much mixing can break up the vermiculite so you get less volume and more weight per pour.
Even though the vermicrete is light once it dries, its pretty heavy from all the water while pouring it, so don't go for big batches. Once you pour it, you can scree it off and make sure its packed tightly, but otherwise it doesn't take a lot of tooling.
Attached shows the roof over the oven complex. This is pour of 8:1 vermicrete about 1.5 inches thick over a corrugated tin. Note the second pic is from the top of the dam and about the same angle as one my pics above showing the dome in place. Still have to finish the stucco on the back of the complex. The pipes sticking through are the handles for my pizza tools...little hint I picked up here to get them out of the way.
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baking expert seeks oven expert. MHGSOH!!-roofed.jpg   baking expert seeks oven expert. MHGSOH!!-roof-above.jpg  
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  #26  
Old 01-29-2008, 05:25 AM
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Default Re: baking expert seeks oven expert. MHGSOH!!

thanks guys. checked out the vermiculite site- based in my home town! lincoln, lincolnshire ENGLAND. so will call them for advice before mixing and pouring.
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  #27  
Old 01-29-2008, 02:06 PM
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Default Re: baking expert seeks oven expert. MHGSOH!!

Michael,

Keep us posted. Looks like you're off and running; no looking back now. As a personal favour to me, drop in to Lincoln Cathedral. One of my favourite spots in England. Umm, York, Canterbury??

Jim
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  #28  
Old 01-30-2008, 09:24 AM
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Default Re: baking expert seeks oven expert. MHGSOH!!

ok jim. lincoln is a very beautiful place, will doff my cap to the little imp! living on the road now i get to some very beautiful places, so if your ever heading over to the uk i'd be happy to pass on a few tips.
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  #29  
Old 01-30-2008, 11:51 AM
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Default Re: baking expert seeks oven expert. MHGSOH!!

CVDuke,

Maybe you could have used a "dogaloo" as the inside mold? I saw that mentioned somewhere on this forum, but what they guy did was section it and pour in layers.
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  #30  
Old 01-30-2008, 05:19 PM
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Default Re: baking expert seeks oven expert. MHGSOH!!

Inside molds dont work too well when making ferro-concrete structures. To make them, you make a wire armature of couple layers of chicken wire interspersed with heavier reinforcing wire. Its pretty important to be able to press the portland concrete mix firmly into the wire, so usually you have to get to both sides. Having said, I'm working with a friend to make a of press that we will use to make 3' X 4' (1 inch thickness) flat ferro-cement panels... this would only press the mortar in from one side but it would be done with more pressure than you get from hand packing
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