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jcg31 03-10-2008 08:10 PM

Another Cracked Dome
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Hello All,

I thought my curing days were done. Upon removal of the Kaowool I found an undercoating of soot and a crack. Upon closer examination of the inside of the dome, the crack was easy to find. I took a look at the photo I posted after the first fire and discovered that it was present with that photo after the first 300 degree fire, I just didn’t notice it. For weeks before I started the curing fires the halogen had been burning round the clock and the top of the dome was at 140 degrees, so I had little reluctance to starting the fires at 300, but in hindsight that was a bit too aggressive. Had I to do it over, perhaps one day at 200 and the next at 250 before hitting 300.

So, I have a fairly significant crack that runs down the left side of the dome. Given the soot it is obviously seeping smoke at some point but I had the oven up to 900 degrees yesterday and no smoke was coming through.

I have about ½” of mortar cladding over the exterior of the oven.
What I was thinking to do for a fix was to grind out the crack to make it ½” wide for the entire crack length in the cladding and then grind out the cracks in the brick below about ¼” wide for the length and about 1” into the brick. After the grind I was going to fill with refractory mortar.

Can someone please advise me on this approach? Is mortar the way to go or would furnace caulk be preferable? Should I attempt this when the oven is hot or a bit cooler? Afterwards do I re-cure?

Thanks for any help. And for everyone who posted their experience with cracks in their dome, many thanks, you preserved my sanity. My initial state of mind when first discovering the crack was something less than cheery.


Xabia Jim 03-11-2008 02:58 AM

Re: Another Cracked Dome
Sorry about the crack neighbor.....

As a student of stone masonry, (anyone remember Ken Kern?)
your crack is very interesting....look very closely at the photograph and you'll notice that a lot of the brick joints below the crack (4 or 5?) seem to line up as well as the one over it.

This is a problem with stone or brickwork when too many of the vertical joints are allowed to line're asking for a crack because of the weakened structure. One always has to be careful that the next upper stone or brick lines up over the center of the lower joint, much as possible that is. One or two vertical joints lining up is okay but the more you allow to line up without a bridge, the more likely that's the location the crack will form.

Sorry it's not much help to you now Jim ...but might help other builders.

I also wonder how many crack free domes exist after using them.

Love your crack, it's character.

RCLake 03-11-2008 06:22 AM

Re: Another Cracked Dome
Sorry to hear that Jim, I'm beginning to resign myself that cracks will appear but the WFO will work just fine. As I've stated, when I took my blanket off I noticed 4-5 spots of soot marks, so I'll mark it on the oven and watch it. From the outside I can see a crack following the mortar line starting at the top left of my arch, a zig-zag. Haven't seen anything inside yet, but it's real sooty in there, surprised how clean your dome looks.

jcg31 03-11-2008 06:42 AM

Re: Another Cracked Dome

Originally Posted by RCLake (Post 26210)
, surprised how clean your dome looks.

Yeah, that photo was taken after the first day of 300 degree fires so just a slight coating of smoke. Now it is completely black. Any thouhts on repair approach?

Dutchoven 03-11-2008 08:09 AM

Re: Another Cracked Dome
Your repair approach makes good sense. I do think you should wait a bit though. The crack is through a brick which means the dome wants to "expand" in that area and as XJim noticed it has to do with the head joints or "perpendicular" joints lining up or being very close. When bricks or blocks are "stacked" rather than "bonded" each stack is essentially a wall in itself. One of the stacks, or an individual brick in one of those stacks, that are below the cracked brick must be expanding slightly different than the other. This is levering against the one on the top and made it crack. If you wait a bit you may find the crack will stabilize with time and the continued heating and cooling and then it would be a good time to repair as you stated. If you do it too soon, a similar crack may occur further up which would place it in the top 3 rings of your oven(you see that there is a head joint directly above the crack also).
I hope this helps some!
Sorry about the crack!

Kemo 03-11-2008 10:34 AM

Re: Another Cracked Dome
is there such a thing as a WFO without a crack?

gjbingham 03-11-2008 10:57 AM

Re: Another Cracked Dome
It doesn't look too significant to me. I think I'd leave it alone. Your cladding should bond everything together on the outside.

I think that cracks are a natural result of thermal expansion/contraction of the bricks during heating/cooling. Any uneveness in the application of heat across the dome (ie: top of dome getting the early heat first) causes stresses as the warmer spots expand faster than the cooler areas (my own hypothesis). My guess is that if you repair the crack as you describe, you're probably going to get it back again in the same spot or develop one somewhere else.

Who knows Jim? The repair might be worth a try. I doubt it will hurt.

Xabia Jim 03-11-2008 11:15 AM

Re: Another Cracked Dome
I'd agree in not being in too much of a hurry to address it. It may actually get worse before it get's better. Use it for a while and let it "work" a bit, then if it's still bothering you give it a grind and fill it.

I'd suggest that a lot of our cracks in ovens are smaller ones that actually occurr along the brick/mortar interface so they don't bother us as much.


Acoma 03-11-2008 11:56 AM

Re: Another Cracked Dome
Jim and RC, would you both say that you are happy with the new curing method, or if to redo, you would go the the old way?

RCLake 03-11-2008 01:39 PM

Re: Another Cracked Dome
I'm totaling in favor of it, I've love tending the fire during the day. Gives me a good reason to take breaks from other activities. I'm adding two days for 750 & 800 temps.

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