Author Topic: Concrete recipe for Weber mod? (Read 10046 times)

Bada Bing · « **on:** June 28, 2011, 04:02:27 PM »

I haven't seen an actual how-to on creating my own version of the Frankenweber, where you mold a dome to fit on top of the Weber kettle. My goal is a wood- or coal-fired oven on the Weber platform.

Forno-Bravo website gives these ratios under "insulating concrete" in their glossary:

"A mix of 6 parts Vermiculite or Perlite:1 part Portland cement to make an insulating product which can be used in the Insulating Hearth and for dome insulation in certain types of enclosure."

Are those parts by weight or volume? I have coarse vermiculate and also some perlite around--they weigh practically nothing. I don't want to waste it with unnecessary experimentation.

Also, I am wondering if the texture of this cement is such that I can coat the inside of a kettle dome and then also have it lie thick enough not to require an inner mold.

Finally, I'm wondering if the weber kettle dome is a little low for this purpose: would it help to create a vertical skirt around the dome before using it as a mold?

Thanks for any tips!

shuboyje · « **Reply #1 on:** June 28, 2011, 10:43:12 PM »

I'm not really sure where to begin here. In my mind there are a lot of issues to work through to make this a go.

Insulating concrete like you reference made with portland and vermiculite/perlite is not for direct fire contact. What you need is a refractory material. Anything portland based will not work. Even with commercial refractories you would want a dense castable not an insulating castable IMHO. Dense castables are stronger and better suited for fire contact. Problem is for an effective oven you then need insulation on top of that. This all gets pretty big, pretty complex and pretty heavy to get on a weber grill and by the time you are done you would be better off just building a small cast oven and forgetting about the grill.

If you want to turn a weber grill into a small portable pizza oven the little black egg is the only way to go, and I am a STAUNCH wood fired guy so that says a lot.

mnjesse · « **Reply #2 on:** July 05, 2011, 10:15:37 PM »

Here is a concrete recipe: http://www.backyardmetalcasting.com/refractories.html
Don found this website and posted it when I had a similar question. I am going to be trying it out this week when I get some time. I will let you know how it goes.

carbon · « **Reply #3 on:** July 06, 2011, 06:17:28 PM »

Perlcrete or vermicrete should not be exposed to direct flames. These mixtures may work over the kettle lid. It also should not be exposed in its raw form as they tend to crumble easily. They are most commonly finished with stucco.

meatboy · « **Reply #4 on:** September 08, 2011, 02:55:11 AM »

...here is my attempt. I just couldn't imagine how a higher refractory cement : perlite ratio than 1:2 is possible. All above was so brickle that i wasn't able to use it. Now the parts are maybe too heavy. The ring is 29lb (but not completely dry), and the top also...

shuboyje · « **Reply #5 on:** September 08, 2011, 09:20:12 PM »

Your casting looks really nice, but I do have a few concerns.

First the simple one. How high is your dome? If you plan to fire from bellow like I assume you do I think it is gonna be way to high. Top heat is gonna be your biggest issue, as it is with all ovens heated from the bottom, and keeping the dome low as possible is gonna be key.

Finally, what type of cement did you use to tie that all together? I'm gonna assume Portland, but am hoping it was calcium aluminate or something else refractory. Lately it seems like lots of people want to copy the frankenweber, and I have no idea why. The oven is poorly to nearly un documented and what little we do know includes that fact that it has been rebuilt at least once. The use of perlite and portland cement for the oven dome goes against thousands of years of knowledge and thousands of functional ovens well documented online. One guy does it with questionable methods and results and suddenly everyone wants to follow suit.

Outside of that I think I basically voiced my concerns in my post a few up.

meatboy · « **Reply #6 on:** September 09, 2011, 03:02:58 AM »

1. i build the "oven" because i don't have the place and the money for a real WFO
2. i used refractory cement + perlite
3. the ring's height is 7.5", + 2" for the dome. I use two pizzastones, one is 2", the other 0.8". So the dome is 6.7" away from the pizza, and because it's a WFO with burning wood next to the pizza it's enough!

Ev · « **Reply #7 on:** September 09, 2011, 06:50:08 AM »

I think at this point, all you can do is try it out. If it's too tall, just grind off a half inch or so at a time until you think it's right. I'll be watching your progress as I'm soon going to be helping Norma build one like yours, so please post your results.

shuboyje · « **Reply #8 on:** September 09, 2011, 09:44:46 AM »

I'm not suggesting building a full on brick oven in the classical sense. My point is it's proven fact that you want dense material as a hot face surrounded by insulation. A 2:1 mix of perlite and refractory gives you neither insulation or conductive thermal mass. It's gonna kinda heat up, kinda conduct heat, and kinda insulate.

On the other point, your kettle is what, 22"? Casting looks 2" thick so now you have 18". There is a guy around with a 21" oven and he can only cook 8" pies with a fire in. Fired from the bottom will give you way more room for bigger pies, but the dome will need to be much lower.

I'm not trying to be a jerk, just trying to help you get to a functional oven.

TXCraig1 · « **Reply #9 on:** September 09, 2011, 10:26:52 AM »

I agree with Steve that you just have to try it out and go from there. Personally, I'm optimistic about his chances for success.

CL

shuboyje · « **Reply #10 on:** September 09, 2011, 12:29:41 PM »

Here is a very similar recent conversation that resulted in a very small oven that works well and the owner is happy with:

http://www.fornobravo.com/forum/f2/perlite-mizzou-castable-16351.html

buceriasdon · « **Reply #11 on:** September 09, 2011, 05:12:47 PM »

Very nice looking casting! Well done, I hope you documented how you accomplished your work as I know people will want to know more about this oven. The furnaces I have built using this type of material can reach temperatures required for melting bronze with no ill effects and those temps are at least three times the temp you want for pizza baking. Bronze becomes molten at around 1600 degrees F., the graphite crucible becomes red from the heat, I'm sure these furnaces run well over 2200 degrees. Keep us informed as to your progress.
Don

mnjesse · « **Reply #12 on:** September 13, 2011, 11:07:22 AM »

Quote from: shuboyje on September 09, 2011, 12:29:41 PM

Here is a very similar recent conversation that resulted in a very small oven that works well and the owner is happy with:

http://www.fornobravo.com/forum/f2/perlite-mizzou-castable-16351.html

This looks like a very affordable backyard oven. What would something like that cost? It looks like it is much cheaper than a traditional woodfire oven.

shuboyje · « **Reply #13 on:** September 13, 2011, 12:28:45 PM »

As a rough guess I'd say about $60 in castable, $30 in fire bricks, $20 in perlite, and $10 in Portland cement would get you very close to the oven minus the stand.

mnjesse · « **Reply #14 on:** September 13, 2011, 05:02:39 PM »

I live in Fargo ND which has temperature extremes (-40 Fahrenheit in the winter and up to 105 F in the summer). How would an oven like this withstand those types of changes? Would it be prone to cracking? Are other woodfire oven styles better able to handle these types of temperature changes? Thanks

shuboyje · « **Reply #15 on:** September 13, 2011, 05:23:38 PM »

The great thing about an oven like that is you can build it on a rolling stand and move it inside when it's not in use. If that's not an option then you need to built a water tight enclosure. So long as the oven stays dry the elements shouldn't be an issue.

SELES · « **Reply #16 on:** January 09, 2012, 11:45:48 PM »

How is this oven working out for you? The casting is real nice and I'm wondering if you'll share your method.

akuban · « **Reply #17 on:** January 17, 2012, 04:23:00 PM »

Meatboy: That is a beautiful casting. Do you have any pics showing the mold you used? My winter project is to build a FrankenForge in time for spring cooking. Seconding SELES here: How is this working out?

SELES · « **Reply #18 on:** January 19, 2012, 09:16:38 PM »

Quote from: akuban on January 17, 2012, 04:23:00 PM

Meatboy: That is a beautiful casting. Do you have any pics showing the mold you used? My winter project is to build a FrankenForge in time for spring cooking. Seconding SELES here: How is this working out?

My goal as well akuban.

I've been thinking a lot about how this might have been cast and I'm leaning towards metal flashing and a 2X4. Some of the pictures show what look to be seams in the mold which in turned me on to the idea of flashing. I could be way off though, this casting looks maybe too clean for that. However, flashing seems like it's common, cheap and rigid enough to be a worthy experiment and Don's recipe for homemade refractory is relatively inexpensive. So I think as soon as I can pull away from work long enough to pick this stuff up I'm going to give it a shot.

Btw, I noticed your in Astoria and it got me reminiscing about those sausage sandwiches out in front of Home Depot on Northern, one of those and a snapple is the jam.

akuban · « **Reply #19 on:** January 23, 2012, 11:31:16 AM »

Yeah. I had the same idea with metal flashing. I think two concentric rings held together by a combo of bolts-and-wingnuts as spacers.

Yes, I'm in Astoria.* So I'll probably be heading to that Home Depot for some supplies -- if I can't find them readily in my neighborhood.

* I like Rose & Joe's, Rizzo's, and Rosario's Deli for slices.

Author Topic: Concrete recipe for Weber mod? (Read 10046 times)

buceriasdon