Michigan WFO Brick Oven Photos Discuss Michigan WFO in the Good Background Information forums; Mike, Nope. Mine was a perfectly fine, 9x13 clay flue 2' long setting on the opening. The gases are hottest ...

[Lars]

Mike,
Nope.
Mine was a perfectly fine, 9x13 clay flue 2' long setting on the opening. The gases are hottest above the vent. If it is going to crack, the first piece will crack first. I had a taper in the arch vent ( firebrick) , and actually, the opening to my flue was a good 1/2" smaller all around then the inside of the flue.



Lars.

[dmun]

Dmum, ( Is it James?)
I think if you were to extract your flue tiles that have been in your chimney ( above a wood fire place) that you would find several that have cracked. That is only my guess.

It's David, by the way, Dmun is my father's old fraternity nickname, from his first initial (All Munro men have D first names Douglas, Donald, David etc) and the first part of the last name.

I think all the flue tiles that cracked have been fired before masonry chimneys were built around them. Code specifies a half inch of air space between the flue tile and the masonry enclosure. My split cone flue tile, the hottest part, was covered in refractory blanket and buried in perlite concrete, up to the level of the support slab above the oven, and the tile stack was provided with the airspace between the flue tile and chimney above that.

I've always held that the firing of bare domes contributed to cracking, but my brick dome cracked too, and it was insulated and cured for the better part of a year before the first fire.

All the flue tiles that have cracked were fired out in the open, as far as i can recall.

[Lars]

David,
Of course, Dmun makes one think of 'demon'. For some reason I got you confused with someone else, sorry about that.

I think the tiles being 'out in the open' and cracking may be a clue. I think the bottom line on this issue is that the oven dome WILL crack, the vent/arch WILL crack under heat, and the flue may or may not crack. The solution, as far as my next oven ( if there were to be one) would be to isolate the inner (firebrick structure) with loose vermiculite or blanket from the outer structure, and then let it crack.

I purposefully buttressed my firebrick arches with my outer brick. I just underestimated the amount of heat and expansion the arches would see. I think if I had it to do over, I would have buttressed them with firebrick, or re-built them, THEN do the outer arch and enclosure with at least a 1/2" space and NO physical connection between.

Today I am taking my Harborfreight thermometer out for a small fire to get an idea of temperatures. Should be fun.

I just went ahead and bricked it up, knowing that the crack will likely open up again when fired. I think there may be a way to fill the mortar joint while it is up to temp... not very sure, though. ( see attached pic)

L.

[mfiore]

Originally Posted by dmun

All the flue tiles that have cracked were fired out in the open, as far as i can recall.

Sounds reasonable. What do you think I should do at this point?

A) tear it all out and put in a fresh one (painful)
B) Try to patch with more heatstop
C) Use some furnace cement (is that the correct stuff people have used for the dome cracks)
D) Tear it out and put in a stainless steel one
E) Cover it up and ignore


???

[mfiore]

Originally Posted by dmun

All the flue tiles that have cracked were fired out in the open, as far as i can recall.

David,

I thought about that some more. If there is usually nothing but air between the flu liner and the masonry throughout the chimney run, then why do you suppose it makes a difference if the flue tiles were out in the open or exposed?

Mine, for example, was out in the open for the firing, but has been covered secure and dry under tarp all year long. It's not wet.

Also, I don't intend on building a true masonry chimney. I am framing a box around to install stone veneer. I don't know if that makes a difference.

[dmun]

Sounds reasonable. What do you think I should do at this point?

A) tear it all out and put in a fresh one (painful)
B) Try to patch with more heatstop
C) Use some furnace cement (is that the correct stuff people have used for the dome cracks)
D) Tear it out and put in a stainless steel one
E) Cover it up and ignore

I vote for "C". Heatstop is the stuff they sell to stick flue tile segments together. I patched my angled pieces with heatstop, no problem.

[Lars]

Mike,

You saw what I did... a combo of your option C. and E.

If it is going to crack anyway, why keep trying to replace it?

Perhaps some type of flexible heat resistant silicon ( recommended by a local fireplace installer) would allow it to flex. I haven't looked for this stuff yet.

Also, there is a very small amount of smoke/gas that would come through the crack, right?

Lars.

[mfiore]

My vertical cracks in the back of the chimney flue are hairline once they cooled off. I caked more HeatStop mortar all over them. At least now I don't see them. I don't think they'll cause any problems, even if they reoccur.

I think I'll insulate around the chimney flue with some vermiculite/concrete mix before enclosing. This might help keep temps more constant at the stress points.

[Lars]

Mike,
Read my post in my CRA|CK!!! thread. All crack issues have become total NON issues.

Lars.

[mfiore]

I've been following your progress with the cracks, Lars. I think you're right

I finished the bulk of the steel framing for the enclosure today. Other than an occasional brace I might need to add for support once I install the cement board, I'm done with this phase. I enjoyed it initially. It then became a real pain (literally, my hands and arms are really nicked up!).



I'm still not sure how long I want my overhangs to be. I'll wait until some of the stone goes up. I put a length of tracking on the ends of the trusses temporarily. Mainly because I was sick of hitting my forehead on those sharp edges!