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]

Re: Flue arch crack: how to fix?

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]

Re: Flue arch crack: how to fix?

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]

Re: Flue arch crack: how to fix?

Thanks guys, will play it by ear...

(another possibility might be muffler sealant?)

Rgds,

LMH

[dusty]

Re: Flue arch crack: how to fix?

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]

Re: Flue arch crack: how to fix?

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]

Re: Flue arch crack: how to fix?

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]

Re: Flue arch crack: how to fix?

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]

Re: Flue arch crack: how to fix?

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]

Re: Flue arch crack: how to fix?

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

[DaveHI]

Re: Flue arch crack: how to fix?

I did the following:

While cold, used angle grinder and diamond blade to vee notch the crack as much as I could. Opened it up to say 1/2 inch at the top and maybe 1 inch to 1.5 inches in.

Then fired the oven to about 500-600 or so to get the crack opened up as much as it would open.

While hot, put the black furnace goo down in the crack. Wore gloves and shoved the goop down in as far as I could get it to go. I flows pretty good once it's hot in there. Filled the entire crack and notch back to a flush surface at the top.

At the very front face of the arch (the only area that will be visible once my enclosure is in place) I caulked the crack with mortar patch caulk. Hit it with the plumber's torch (my fire starter!) to make sure it reached the 500F temp to make it set hard. That worked fine, but wait a bit to test it with finger. Ouch.

Let the oven cool.

Once cool, I mixed up mortar and put a layer over the patched cracked area and since I was dirty and the mortar mix was there, hit most of the dome about 1/2-1 inch deep. It's so humid here that with mortar/portland it's best to just use it up.

Let it cure for a few days and re-fired to test. Didn't see much of anything so I insulated the dome, built my enclosure and crossed fingers. I can still access the dome area by removing a piece of rock board that isn't permanently screwed down yet. Don't see any smoke leaking, hot spots or much of anything. And I've had 3 serious firing sessions with 6-10 pizzas, chicken, bit of salmon and a dozen loaves of bread.

Have see one other tiny crack on the other side of the arch developing. When the mood strikes, I'll patch that with the caulk as well. Since it dries grey, you can't tell it from the mortar.

I don't blame you for not wanting to join this club. My own confession is I felt a little better after seeing your crack pictures. Your brick work is much nicer than mine. I'd felt bad that my half assed efforts there were the problem.

[carioca]

Re: Flue arch crack: how to fix?

Welcome to the club.

......

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).

''''''''''''

Good advice mate! I'll see if I can source some of this goo stuff here in Oz - no doubt it won't come in at $25, but...

Cheers,

LMH

[DaveHI]

Re: Flue arch crack: how to fix?

this is the cement I bought

Find furnace at HardwareStore.com

the fireplace mortar is at the end of row 3.

Good luck with it.

[dusty]

Re: Flue arch crack: how to fix?

Thanks Dave. Very good advice. I went to the hardware store in my neighbor hood and got some of the black goo stuff. I put it on (in) the back crack when the oven was hot. I didn't do the front crack, the one I am concerned about. Thought I would wait to see how it worked on the other one. It dried very hard by the time the oven cooled. Looks like it worked beautifully but I may notch the front one to be extra sure.
I knoced my river-rock keystone out of my front arch and plan on resetting it when I solve the crack problem.

Thanks again.

dusty

Any club dues?

[DaveHI]

Re: Flue arch crack: how to fix?

no prob.

You may always fight differential expansion leading to cracks between rock and brick. I've no idea how different their coefficients of expansion are but it can't be zero. It looks pretty cool so keep it even if you have to live with a hairline.