Flue arch crack: how to fix?

[DaveHI]

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]

Originally Posted by DaveHI

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]

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]

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]

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.

[dusty]

Originally Posted by DaveHI

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.

I understand what you mean. Hopefully the front arch won't get hot enough for expantion differentials to be a problem. I am very sure that it cracked the first time due to the rear arch crack. I am hoping that if I can stabilize that one, the front arch won't crack again. Fingers crossed.

dusty

[DaveHI]

mine gets pretty damn hot. The stack gases are heating one side of those bricks. When I get the fire a bit too big, flames get sucked into the plenum leading to the stack a bit. I've never hit the front face with my IR thermometer but I'd have to guess 200 F ish. the faces in the plenum are much hotter.

If I fire any time soon (too busy this weekend) I'll put up some figs.

[dusty]

Well, I will just have to deal with it. Hopefully I won't have to deal with a crack in front, but if I do, then I guess I do.

dusty