Closing the dome

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Hello all,

I was asked about the sizes of the gap between the bricks in the last
few chains. How accurate everyone has been with the last few chains?
How big are the gaps between the bricks? How is it behaving after you
started using it?

Robert, is your "plug" still working?

What about pouring your plug on the side, and then setting it in
place, filling the gaps with refractory mortar?

I have photos of the inside of the dome in a professional made oven
which I will post -- it shows lot of nice cuts. That could be helpful
for new builders. Also, the ancient ovens had a concrete disk that
replaced the last few chains. I have asked a couple of academics what
type of concrete they think the ancient builders used. We'll see.

James

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instead of cutting all the bricks in half i have cut the bricks for the last 6 or seven rows into a trapeze shape.
i made 4 cuts per brick with a circlular saw, easy and fast, getting 2 trapeze shape pieces and 3 very small triangle pieces which i used later to fill into gaps.
i tried to keep my gaps very small.

also, the pictures you posted of the profesionally built dome, show a dome from the inside where the gaps seem to have been filled in with mortar throughout??
has anyone else filled in the small gaps.?
i have always wondered if that makes a difference in heat-up time and aircirculation?

simone

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instead of cutting all the bricks in half i have cut the bricks for
> the last 6 or seven rows into a trapeze shape.
> i made 4 cuts per brick with a circlular saw, easy and fast, getting 2
> trapeze shape pieces and 3 very small triangle pieces which i used
> later to fill into gaps.
> i tried to keep my gaps very small.

### That was trickier than I thought most people would want to do
that's why except for the last couple of bricks all of mine were
halves. My "keystone" which went in last was actually somewhat
pentagonal in shape.

>
> also, the pictures you posted of the profesionally built dome, show
> a dome from the inside where the gaps seem to have been filled in with
> mortar throughout??

### Yeah, sloppy work huh? <grin>

> has anyone else filled in the small gaps.?

### The gaps in mine are paper thickness. Up at the top there might
have been some that were 1/4" or so but those are mortared from above.
I didn't bother to mortar any others. If you want to you can fill them
in with fireplace or furnace cement. It comes in caulking tubes making
it easy to work with and cures under fire to 2000F+ strength.

> i have always wondered if that makes a difference in heat-up time and
> aircirculation?

### If it does then my oven will be hot before I start the fire
<grin>. My heatup is consistently 1/2 hr (+- 5 min) using 2 cu ft of
dry oak. I can get that down to about 15ish min using my propane
burner. Keep the dome height to 20-22" (for a 42" dia oven) and the
convection currents will be fine regardless of little edges and
"imperfections" in the surface. The first time you have a full fire
and watch the flames hit the ceiling and bend halfway down the arch
you'll realize the tolerances aren't as critical as we tend to think
they might be.

jim

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i had large gaps at the top. i just figured what the heck; *tension would keep the bricks together and even if the mortar fell out of the gaps, there was no way i was going to get the fire hot enough to burn thru vermiculite. i guess the issue is whether exposed angles and corners of bricks will be more likely to chip away over time from*contraction and expansion. i can't begin to imagine how the gaps would effect performance to the point where it would be noticable. *i'm very pleased with the performance of my oven (but then again, i really don't have anything else to compare it too). *

with respect to my "plug" ...

knock on wood, it seems to be*holding together just fine (firing the oven three times per week since*late september). i did pour a "test plug" in a dixie cup and then threw that plug directly into the first three or four fires just to see*what would*happen to the*brick / mortar concrete that the plug consisted of. it seems to retain its strength pretty well except for the edges, which could be crumbled away with a screwdriver.**my chimney throat is somewhat constricted by the same stuff that i made the plug from and i have tried to remove it from the chimney to no avail. it's still like iron. the first time i tried to get it out i used so much force that i ended up collapsing the front arch but still couldn't get it out.*so i just rebuilt the arch and said the heck with it. *of course that area doesn't get as hot as the top of the dome but its still a little reassuring.

if the plug deteriorates, then i will pour another one.*in fact, unless the oven simply collapses, this will be the way i will make all*my repairs. kind of like prehistoric brain surgury. i will just drill a hole in the dome into the area of the missing / damaged brick.*seal the area from the inside and then pour (or pump) in a mixture of whatever seems to work the best. (this will result in the minimum amount of damage to the mosaic.)**

i think pouring it directly into the top is the best way to go, rather than pouring it on the side.*in my case, the bottom of the plug area was sealed by metal flashing and modeling clay (held up by a bunch of bricks) and the pour filled all the rough nooks and crannies that had developed in the last course of real bricks. it looked to be locked in really tight. perhaps the exact fit might present*some contraction / expansion issues but*it seems to me that the expansion / contraction issue may be slightly overblown (especially for a round oven).*

so here's another reason to use a round oven -- it just seems (purely from an amateur's*eyeball) that a round oven is going to be much more forgiving of expansion and contraction than a barrel vault because (1) there*are fewer bricks at the very top of the arch and (2)*each brick in a round oven is*supported by more*surrounding bricks than is the case with a barrel vault.**