Is this crack catastrophic or salvageable?

[Carbivore]

Hey guys, I'm building a 40" home brew cement oven. I started the curing process as recommended on this forum, slowly increasing the fire size adding approx 100F each time, and letting the oven cool fully before firing again.

Somewhere along the line I started developing hairline cracks in the refractory dome (I wanted to cure & dry out the refractory dome fully before adding insulation layers). I read on here that if you don't have cracks, you probably did something wrong. Okay, fair enough. At one point I added my ceramic wool blanket on top, figuring the easy-to-add insulation would help things, however then I noticed it got soaking wet. I suspected steam from the smoke coming through the cracks, though of course now I realize it was quite possibly water coming out of the cement as well. Being concerned about the potential for moisture to be going up into the insulation layers later on I applied some fireplace sealer cement stuff (https://www.canadiantire.ca/en/pdp/i...-0642704p.html) to the cracks in the hopes of containing any moisture down the line. Then I started increasing temps again, and the sealer just re-cracked along the same lines. Oh well.

My most recent fire got up to about 550F on the floor of the oven, still 300F shy of target, and afterwards I noticed a rather large crack that goes all the way from floor to ceiling on the dome. I'd say it's about 1/8th of a inch at largest - you can see light through it.

This is rather worrying to me. I'd really appreciate it if you guys could weigh in on whether or not you feel this crack is salvageable or what. At this point I'm not sure what to do. Please help! (see pics)

Also - is moisture from the fire going up into the insulation layers a problem or am I off base here?

Many thanks,
Jonathan

[david s]

Driving out the water from the casting is more likely to cause cracking if done when the dome is uninsulated because there is a greater difference in temperature from the inside to the outside. Yes it does make the insulation wet but the fire will eventually drive it out. Also a one piece dome is more likely to crack because of the huge temperature difference not allowing for expansion. A multi piece casting is better but more difficult to engineer. The addition of polypropylene burn out fibres in the mix helps reduce cracking problems. Did you add these? A crack in the oven should not interfere with the way it cooks and because the hemisphere is a self supporting structure, it won’t collapse. There are two kinds of oven owners, those that have ovens with cracks and those that have ovens who lie about their ovens having cracks.

[Les]

David, I read this a lot about cracks but I'll be damned if I can see one. I can see where some of my brick shifted a bit but not cracked. I've been using the oven for over 10 years now. Pic's are to big to upload but here is a link. https://1drv.ms/u/s!AoKcmsiG0HokhDD2...76msD?e=E0inPq

[wotavidone]

Les,
I think you might be misunderstanding the definition of a crack as it pertains to a brick oven.
In a decently built brick oven the cracks will be in the mortar not the brick.
The mortar will probably separate from the brick, in fact the mortar is supposed to be softer than the brick so as to make sure it cracks before the brick does.
If your brick has shifted, you have a crack in the mortar brick interface somewhere, but since you can't see the mortar, you can't see the crack.
Cracks in the brick itself seem rare. My oven is built from clay pavers, not firebrick, and I have only one cracked brick that I know of after 7 years.
Regards,
Mick

[wotavidone]

Driving out the water from the casting is more likely to cause cracking if done when the dome is uninsulated because there is a greater difference in temperature from the inside to the outside.

I agree - I tell people to insulate before the oven sees any heat. It's only logical - if you can redcue the temperature differential between inner and outer surfaces, you reduce the internal stresses in the dome.
And you can't see the cracking - outa sight, outa mind

[Les]

Mick, I only used mortar as a "shim" to keep the back of the brick on angle. My whole design / approach was to have the bricks float to their happy place.

[Carbivore]

Thanks guys, I really appreciate all the input.

My takeaway here - if the dome hasn't fallen over yet, then it's still usable. Is that about right? It's like what they say about brand new pickups... the first one's a scratch, the rest are character.

Going forward, I will insulate before firing any further. I had thought about the inner/outer temperature differential, and reasoned it would lead to more stress on the dome, however I was certain I'd read somewhere it was best to eliminate as much moisture as possible from the inner dome before adding further layers.

[Les]

Carbivore, I saw one oven that had at least a 5/8 inch crack from top to bottom. He covered it with the blanket and moved on. The oven performed very well. Pretty sure you are golden - happy cooking :-)

[Carbivore]

Carbivore, I saw one oven that had at least a 5/8 inch crack from top to bottom. He covered it with the blanket and moved on. The oven performed very well. Pretty sure you are golden - happy cooking :-)

I can't tell you how reassuring that is to hear!!

PS I love your tagline about skydiving.

[wotavidone]

Mick, I only used mortar as a "shim" to keep the back of the brick on angle. My whole design / approach was to have the bricks float to their happy place.

Exactly - no visible mortar, no visible cracking.

[Chach]

David, I read this a lot about cracks but I'll be damned if I can see one. I can see where some of my brick shifted a bit but not cracked. I've been using the oven for over 10 years now. Pic's are to big to upload but here is a link. https://1drv.ms/u/s!AoKcmsiG0HokhDD2...76msD?e=E0inPq

Les, your oven is as beautiful as it was the day you finished it.

[Les]

Thanks Chach. It took some effort and at the time I was attempting something that had not been proven. After 10 plus years of operation - it was a win -)

[Chach]

Thanks Chach. It took some effort and at the time I was attempting something that had not been proven. After 10 plus years of operation - it was a win -)

For sure a work of art...do you find yourself using it regularly or does it loose its luster? sorry Carbivore for hijacking your post...

Ricky

[Les]

Ricky, they do lose their luster. ( for us anyway ). Maybe 3 - 5 times a year. We bought a pellet smoker which is a lot faster and cleaner to cook the things that were destined for the Tuscan grill.

[Chach]

Ricky, they do lose their luster. ( for us anyway ). Maybe 3 - 5 times a year. We bought a pellet smoker which is a lot faster and cleaner to cook the things that were destined for the Tuscan grill.

Les, funny I was looking at pellet grills before I started this project. I was looking at traeger grills and camp chef. I eventually want to get one.