Another Cracked Dome

[jcg31]

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 ?? 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 ?? wide for the entire crack length in the cladding and then grind out the cracks in the brick below about ?? 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.

Jim

[Xabia Jim]

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 up...you'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, ....as 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.
XJ

[RCLake]

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]

Re: Another Cracked Dome

, 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]

Re: Another Cracked Dome

Jim
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!
Dutch

[Kemo]

Re: Another Cracked Dome

is there such a thing as a WFO without a crack?

[gjbingham]

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]

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.

XJ

[Acoma]

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]

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.

[thebadger]

Re: Another Cracked Dome

Gang,

Hoping to start the dome once I finish the hearth in the next month.

I've heard a lot about cracks. It seems the best way to prevent is:
Keeping the bricks moist
Staggreing the bricks
Curing strategy

Is there anything else I should know/do to prevent cracking? Or is it like concrete guys say "not a matter of if, but a matter of when."

Thanks
Dick

[gjbingham]

Re: Another Cracked Dome

My thoughts (guesses) for minimizing cracks would be two:

1. Staggaring the mortar joints as much as possible
2. Use Refmix mortar - from what I remember, its thermal expansion properties are most similar to firebrick - I might be wrong on this.

A likely third would be to do custom brick cuts similar to Les, Acoma, Ken and JCG have done recently. This will probably minimize the amount of damage that a crack will produce. (Myself - I wouldn't attempt it. I was a hack with the saw.)

[Acoma]

Re: Another Cracked Dome

I Agree. The thermo properties of the Refmix are most similar to bricks for heat tolerances. Beveling and consistancing, as well as the interior face is imortant. I personally took lot of extra time bonding, moistening, cleaning each brick along the process.

[jcg31]

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?

Unfortunately I have nothing to compare to. I went with the new approach because it made sense to me. I will say the advantage for me from the all day approach was that I learned a great deal about my oven in the process. If you choose to go this way I would start with smaller fires initially, it may add a couple days to the process but probably would be worth it.

That said, it would be good to have those familiar with the expansion dynamics of each process chime in. Heating the oven up and cooling it all the way down as suggested by the original process may serve to "exercise" the oven a bit more.

On the other hand the constant heat certainly makes sense for driving out the moisture. Perhaps a combination of the two methods, where you keep the fires going all day but then instead of putting the door on at night you allow the oven to return to the outdoor temp before the next step of fire.

At this point I have built one oven, It would be good fto hear from all those in the community who have built and cured multiple ovens.

The other question I have seen a number of times on the forum, but have not seen an answer is : Is there a brick oven in use that does not have at least one crack in the dome? At the point I discovered my crack I thought it was the exception, after reading many posts on the subject I am thinking that cracks in the dome are the rule.

Jim

[james]

Re: Another Cracked Dome

It reminds me of the old joke. There are two things that are certain for a new concrete patio. It will crack, and no one will ever steal it.

I think it is just part of the process, where no matter how hard you try and how slowly and accurately you cure you oven, little cracks just happen. It doesn't impair how well your oven will cook or how long it will last, and they really don't tend to grow over time. They settle down and last forever.

I hope this helps.

James