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Lars 06-27-2009 02:39 PM

Keystone CRA|CK Ugh!!!!
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You all say so expect some cracking. I am on my 4th curing fire, my flue does NOT draw well enough, and today, my front brick arch developed a crack in the mortar.

Not only was this a bit of a disappointment, it also seems that I am nowhere near high oven temperature. I have insulated pretty well, but I am not sure where the heat is going! Nothing seems particularly hot, yet the fire is burning pretty hot for 1/2 hr. to 45 min.

To top it all off, I have been experimenting with pizza recipes, and just found out my kitchen oven goes up to 550 degrees. Is the idea of a wood fired oven just a huge urban myth-- will I ever be able to actually cook a pizza in it??

Keystone mortar crack... this is kind of unacceptible. I really think it is a result of a too small flue and the bottom of the bricks heating up while the top ( outside ) edge remains cool.


Fire Igloo in Nebraska --- more like a real igloo!!!

Les 06-27-2009 03:32 PM

Re: Keystone CRA|CK Ugh!!!!
Lars - the crack is no worse than many we have seen. I don't see where the brick can fail. After your face / enclosure brick is complete - it's forgotten. In regard to the heat - I trust you have had a larger fire then what we see. You need the fires of hell - for some time, to get this mass to heat. When the smoke turns to a true gas - I think it will draw very well. I didn't go back and look at how you installed your flue but it looks like the right size.


RTflorida 06-27-2009 04:09 PM

Re: Keystone CRA|CK Ugh!!!!
If you are only on your 4th curing fire (and have followed one of the methods on this forum) you should not even be thinking of pizza yet. AFTER you have finished your curing schedule it is time for the "fires from hell" - and YES, a good fire should scare you a bit the first few times. Also keep in mind that you oven will get better and better, it is still driving out moisture for up to 20 fires or so.
As for the crack - sorry to see it, but not unexpected. I have a similar crack in my arch mortar.....patched it 3 times in 3 yrs and it comes back every time I have an extended burn. Was very pissed the first 2 times, I am resolved to the fact that it is a "character" line that won't go away.
I would wait until you have had at least one good fire from hell to see if any additional cracks develope, then grind out the mortar and repack them...make sure you soak the bricks on either side of the joint with a wet sponge, or the bricks will suck out the moisture and you can guarantee another instant crack. Many folks here have had great success in patching cracks.....I unfortunetly am not one of them.

Good luck......don't lose too much sleep over this, your oven should perform very well once you get entirely through the "process"


Ken524 06-27-2009 06:03 PM

Re: Keystone CRA|CK Ugh!!!!
I had much worse cracks in my vent arch. Mine were so wide, I was able to get mortar in them to patch them. Don't despair, press-on! You'll be fine.

Lars 06-30-2009 09:04 PM

Re: Keystone CRA|CK Ugh!!!!
4 Attachment(s)
After more insulation, a scratch coat of stucco, today we did a little bigger fire. The crack opened up... suddenly there was a high-pitched crack sound... My son and I soon realized the flue had cracked.

I read about this in someone's post. Should I be looking for a replacement, buy a second, or just mortar this one in and forget about the crack?

My front arch crack opened up wider than ever, and the crack basically continues through the whole series of arches and even extends into the dome in the vermiculite and scratch coat of stucco!!!

Really, the arch ( keystone) crack was virtually closed before I lit this fire and now it opened up wider than ever. Additionally, the bricks in the back of the dome started burning white, but not up in the dome...

What about this cracked flue. I have a 9"x13"x2' masonry flue. I am thinking this crack may just be the result of uneven heating and there really may not be a way to successfully use this type of flue on this type of oven.

Thoughts??? should I just mortar it in, put some vermiculite around it? What can I use for expansion joints in masonry?


dougrappe 07-01-2009 06:05 AM

Re: Keystone CRA|CK Ugh!!!!
Lars, I hate when that happens, (I mean the flue cracking) from what I've read the rest of your cracks seem minor, annoying and disappointing for sure but I don't see how it will affect the structural integrity of the oven.

I was trying to find the thread I was reading about Flue-crackage, I think repairing the cracked one in place is an option, but I think you need to let the mortar cure for any repair. There is also some discussion out there of 'furnace repair goop' no experience there but something I am thinking about too.

feelin' your pain,


Lars 07-07-2009 10:50 PM

Re: Keystone CRA|CK Ugh!!!!
1 Attachment(s)
This thread seems as appropriate as any to continue my build details.

I added more brick to the face, mortared in the cracked flue, added vermiculite on the dome between the dome top and the flue, and put a 'scratch' coat of mortar on it.

I know it will fail when heated up, but short of tearing out everything, I am faced with letting it crack, and figuring out a solution, depending on exactly what happens.

It's all a learning experience, right?

dougrappe 07-08-2009 06:24 AM

Re: Keystone CRA|CK Ugh!!!!
Hey Lars, looking good! Nice clean masonry work on that arch enclosure. I have re-started curing fires myself, I want to get some more insulation around the connection to the flue like you did, I think that will help minimize rapid temperature changes and potential cracking.

Thanks for sharing,


blacknoir 07-08-2009 10:31 AM

Re: Keystone CRA|CK Ugh!!!!
Hey Lars, looking good. Are you planning on leaving the dome as is and just build a brick face? I still haven't decided what the heck I'm going to do but I'm 90% sure that I'll be using brick for most of it..

Lars 07-08-2009 10:56 AM

Re: Keystone CRA|CK Ugh!!!!
Hi Shay,
I built up my dome with the vermiculite all around the bottom, then 1" of ceramic blanket and vermiculite/portland over that, then, all over the top of the dome, I used 3" of ceramic blanket and still covered it with the vermiculite/portland. Over that I put a scratch coat of stucco ( 3:1:1/2 ---Fine sand, Portland, lime) which repels the water.

When I put the flue in, I built up ( yesterday) the bricks a little higher still, and shaped the vermiculite coming straight off the top of the dome toward the flue with an 18" diameter rounded shape. ( level, so it sheds water left and right.) then I filled behind the bricks and rounded that back so the water runs left and right of the bricks, pretty much... and I covered that with a 'scratch' coat of stucco.

Next I will make a few fires, and see what cracks... maybe even repair it while it is fired up hot... ( just spraying (with water) the cracks and jamming some portland/fine sand/slurry into the cracks)

After that, I am actually going to put on a 'brown coat' which is the second layer of stucco. Along with the chimney cap, this should make the whole thing weatherproof.

Later still, I will end up burying the back end because it is up against a wall of dirt right now... and I will build in some 'cabinets and counterspace' out of concrete block, stone, and poured concrete flat surfaces....

Oh man, when will I ever be able to use this thing???


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