Flue arch crack: how to fix?

[carioca]

Hi all (those with the unfortunate experience, mainly),

I am halfway thru the series of tempering firings and notice that my flue arch has a crack right at the top (see pic) when it's hot.

What are my best options to deal with this? Keep it open with wedges, wait until it cools, then fill crack with hi-temp mortar and take out the wedges? Do nothing?

Any tips most welcome.

Rgds,

LMH a.k.a. carioca

[gjbingham]

All your ideas sound reasonable to me.

If it was my oven, I think I'd finish the firings and see if any other cracks show up. Your arch design looks good in the one early pic that I saw. The weight of the bricks should lock the whole thing together, so repair may not be necessary.

Just my opinion (which may stink, but I can't smell it)

[Ken524]

I agree with George. Do a few fires before anything else. That's a really tight joint to begin with (nice work!). Beyond working a little hi-temp mortar into it, fixing it would be a challenge.

[carioca]

Thanks guys, will play it by ear...

(another possibility might be muffler sealant?)

Rgds,

LMH

[dusty]

I am in the exact same boat so I will be watching this thread closely. I am not worried that the arch will crumble, I am simply not willing to accept a visible crack right in the front!
I, too, was thinking of wedgeing it open when it is hot and then filling it with mortar when it cools. I suppose I will finish the curing and go from there.
Good luck.

dusty

[Frances]

Same here actually. I'll see what you lot do and how it works, but in all likelyhood I'll just leave it as is.

[carioca]

Originally Posted by dusty

I am in the exact same boat so I will be watching this thread closely. I am not worried that the arch will crumble, I am simply not willing to accept a visible crack right in the front!
I, too, was thinking of wedgeing it open when it is hot and then filling it with mortar when it cools. I suppose I will finish the curing and go from there.
Good luck.

dusty

Hi again,

I smeared some prepared (wet) firebrick cement mix into the crack just to prevent rain from entering - but would you believe it? There's a new crack now on the other side of the keystone, a fraction larger than its sibling!

It's been raining on and off all day, so I haven't worked on the oven or fired it today... but I MAY decide to saw through the remaining mortar in both cracks on either side of the keystone and replace it, nicely buttered with hi-temp mortar, once I am through the firing regime.

Cheers,

LMH

[DaveHI]

Welcome to the club.

on about firing #3 my arch crack appeared. I didn't have my IR thermo yet so no idea if I just over fired it too early or if my brickwork was sub par. I had tried to cut tapered bricks to minimize the size of mortar joints. Getting the Italian mortar to Hawaii wasn't cheap and I knew i'd have to be careful or come up short. Between those cuts not yielding uniform pieces and poor joint thickness control, half brick stagger from row to row didn't hold up from the middle of the back around to the front. Had some too close from row to row. I should have cut some larger blocks to get the stagger back but didnt realize it would be an issue.

My thermal crack started about the middle of my arch and snaked all the way up to the top of the dome. At the arch it was big. I could see fire easily and I'd guess a quarter would have fit in the crack. The rest of the way it was just a crack with no smoking etc. I fired the heck out of it a number of times to see just how bad it would get.

Once it stopped growing, I v notched the crack with my angle grinder and diamond blade. I ordered furnace cement (black goo) and fireplace mortar repair (tube of caulk like material) from Aubuchon Hardward (mainly because they will ship via US mail to Hawaii so the freight only doubles the bill instead of 5X like many of the other sources).

I then fired the heck out of it, pushed the black goo into the crack as far as I could get it and filled the visible crack with the mortar repair. Both need 500 F firing to set properly so I hit the front face with my plumber's torch to make sure it set hard. I then let it cool down and slathered an inch of homemade high temp mortar on the cracked area and the rest of the dome for good measure. Seems to have worked. I've seen no smoking in the enclosure or discoloration of the insulation. Nor do I see/feel hot spots on the insulation.

Not to mention it holds heat very well and I've no prob hitting 1050 dome temps.

Total cost -- about $25 bucks for the various furnace goos including high priced shipping.

Good luck! As long as you aren't indoors and your surround is fireproof it's mostly just aesthetics. And near as I can tell, your friends just want to eat the pie!

[gjbingham]

Good answer DaveHI. I recommend you post that in the tips/tricks forum. That way it's easily found if anyone needs the information in the future.
George

[dusty]

Originally Posted by DaveHI

Welcome to the club.

I then let it cool down and slathered an inch of homemade high temp mortar on the cracked area and the rest of the dome for good measure.

Thanks for the info Dave. I should admit that I didn't want to join your club, but thanks for the warm welcome.

I didn't understand the slathering part. Did you apply a coat of mortar over the entire dome like cladding?
You applied two products to the crack when the dome was still hot?
And, after that, the crack stabilized so you front arch, when repaired, didn't crack again?

Sorry about all the questions. I hope I don't sound panicked. I have just been thinking about it alot and I appriciate the expirenced knowledge.

dusty