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widespreadpizza 04-12-2007 09:01 AM

floor set now debating thickness
 
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Hey all, I have been reading as much as possible regaurding dome thickness and wanted to see what anyone might have for comments. my main concern is heatup time, and the ability to reah vy. high temps without tons of wood. I have been looking at the 1/2 bricks and am just scared at the mass. I have been toying with the 1/3 bricks, and wanted anyones opinion on this method. this would make the uncoated dome 3" thick. let me know what you think. thanks -marc

vtbread 04-12-2007 10:03 AM

Re: floor set now debating thickness
 
hi widespreadpizza,

I am up in you neck of the woods as well, I picked up on your LuiLui related post theotherday, but never go taround to chiming in, I work in WRJ and live in Thetford.

If you are going that thin would it not make sense to cast the whole dome?
As in place a sand form, cover with plastic, mix a stiff refractory over the plastic covered sand and let cure, remove sand and plastic, done.
Then build arch and surround as well as flue (although you could probably cast some of that as well.

Has anyone tried this? I have made large (2.5'x 1.5') slabs for a Russian type masonry heater.

dmun 04-12-2007 10:39 AM

Re: floor set now debating thickness
 
Quote:

Originally Posted by widespreadpizza (Post 9531)
I have been looking at the 1/2 bricks and am just scared at the mass. I have been toying with the 1/3 bricks, and wanted anyones opinion on this method. this would make the uncoated dome 3" thick. let me know what you think.

It might not be quite three inches, since that would make your brick 9 1/4 long. I've been advocating the 1/3 brick build for a number of reasons. First you end up with an oven that's thicker than the commercially made refractory ovens, like the ones from FB, and they seem to work fine. Next, you have an oven that's roughly the same thickness as the brick floor, which current thinking says should be laid directly on the insulation without any additional thermal mass.

The only downside that I can see is that if you are using the homemade fireclay-sand-portland mortar you might have a dome that's not quite as strong as a half-brick dome. Also, the cut side of the brick looks different, and not as nice, as the factory end, but you can put the double-cut bricks in the front where nobody can see them.

If fast heat up is your goal, I'd say go with the 1/3 brick.

widespreadpizza 04-12-2007 10:56 AM

Re: floor set now debating thickness
 
Yeah, I have been concerned about the double cut end not looking so good, but am beginning to stop worrying about it. The factory ends are all alittle chipped anyways and the middle or the brick is a little more of a perfect rectangle. It has crossed my mind to make a checkerboard pattern? I already have 3 bags of heatstop 50 waiting for use so strength shouldnt be an issue. VTBREAD, as far as casting it goes, I already have all the brick and whatnot so I am going to steer clear of that option, although it is a good idea. Being from WRJ do you frequent the 7 barrel by chance? I stop in everytime i go through. Would love to see your oven at some point. thanks and keep the comments coming if you have them. -marc

whocanitbenow 04-12-2007 11:39 AM

Re: floor set now debating thickness
 
Very interested in this topic as well. I like the idea of fast heat, however I am using the homemade fireclay mortar, so I don't know whether I want to do anything that will compromise the structure. Also, I am planning to insulate with the Insulfrax blanket and perlite over that. Does that affect the need for dome strength? How much of a risk to the dome is using the 1/3 brick (and is the homemade mix really that much weaker?)

Chris 04-12-2007 01:36 PM

Re: floor set now debating thickness
 
My 1/3 brick + heatstop 50 oven is doing just fine, after 3 pizza bakes. I have a cracked flue liner, but the dome is intact. I wouldn't expect the insulation method or even the homemade fireclay mortar to significantly affect the strength of the structure relative to the 1/2 brick dome.

Keep in mind, ovens were built and used long before commercial refractory mortars. Just because the new stuff is better, doesn't mean the old stuff is unsuitable.

widespreadpizza 04-12-2007 05:41 PM

Re: floor set now debating thickness
 
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Ok , gonna move forward on the 1/3 brick dome. Now onto the height. Where are people on the 15.5" guideline how has that or is that working for anyone? Like i said I am aiming for fast pizza, Does anyone think that this is too high for my 42 inch dome. also how does this arch look. please ignore the inside line. I was looking at it wrong when I drew it. Thanks for your input -marc

maver 04-12-2007 06:51 PM

Re: floor set now debating thickness
 
I built mine 42" and 18" height. I think 15.5" would be very manageable to build. If you use a 2/3 dome height door, you may get into limitations on what you can slide into the oven come Thanksgiving time, but you'll have no problems with pizza or bread.

As far as dome shape, for strength you want a parabola - yours looks more curved at the sides and flat on the top than I would be comfortable with. The caternary arch is a great way to find the parabola - tack your insulating form board to a wall, mark a horizontal diameter line (42") and the inside oven points on the line (21" from the center on each side), mark your oven height (15.5" or 18", whatever you choose) perpendicularly down from the midpoint of the horizontal line, then tack one end of a chain to one of the points on the horizontal line, and drop the chain through the other point on the horizontal line, take up the slack until the chain passes through your oven height marking, then trace the curve.

james 04-15-2007 10:07 AM

Re: floor set now debating thickness
 
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Hi Marc,
I got your note. I think Maver's concern that your arch seems to have flattened out in the middle makes a lot of sense. It seems as though that curve would be difficult to build, and I would worry about both the possibility of the middle wanting to come in, and the outward (lateral) thrust the center would place on the more vertical bricks.

It isn't the mortar that makes a dome strong, but the way each brick transfers is desire to fall to the ground to the next brick below it, and so on, until you reach the ground. Each brick has to be securely resting on the brick directly below it.

There is another idea I want to add. This has been in the back of my mind for a while, and with more builders considering a lower dome, it want to add it to the conversation. With a lower dome, there is a more aggressive inward arch. To better support that shape, I think builders should consider using a cut angle brick on top of the first course. Also, you might want to consider setting the first course on its end, with the longest side upright. This allows you to build a parabola shape, while still reaching the 15"-16" height you want.

I am attaching an early draft of the idea, and am interested in getting feedback from past and current builders. I am still working on the drawing, but the timing is good -- so I am posting it as is.

James

james 04-15-2007 10:12 AM

Re: floor set now debating thickness
 
Marc,
One more thing. Just a side comment, but the lower dome does not help an oven heat up faster. The advantage is more that the lower dome might be more efficient at bouncing high heat from the fire's flame on your food. Don't knock yourself out for a lower dome just for heat up time.
James


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