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CRACKS!!!!Stress rising - Forno Bravo Forum: The Wood-Fired Oven Community

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CRACKS!!!!Stress rising

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  • CRACKS!!!!Stress rising

    After a long week to dry out, I have started my cure. 2 days in , CRACKS. It looks like the dome pieces are separated by about 1/8" ,back wall looks about a 1" deep all around and like there are patch areas on the side walls.

    I hope others have had this and say " don't worry, have a cold one and relax"
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  • #2
    Re: CRACKS!!!!Stress rising

    I think cracks are part of the experience! I have a Pompeii oven so someone else with a Toscana can comment on your situation. I believe the thing to look for is if smoke is coming out of the cracks. If yes then you need to fill them in (I filled mine from the outside before the insulation was put on.) If not then consider them to be useful, natural expansion joints! So I say relax!

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    • #3
      Re: CRACKS!!!!Stress rising

      Originally posted by austinmc View Post
      After a long week to dry out, I have started my cure. 2 days in , CRACKS. It looks like the dome pieces are separated by about 1/8" ,back wall looks about a 1" deep all around and like there are patch areas on the side walls.

      I hope others have had this and say " don't worry, have a cold one and relax"
      Did you cure it with the blanket on or off? It looks like a cast oven, is it in sections or a one piece dome?
      Don't worry too much, because it is a dome it is self supporting and can't collapse. You must have gone too fast with the fire. You can't go too slow, but you can go too fast.If you bought it from a manufacturer ask them to look at it.
      Kindled with zeal and fired with passion.

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      • #4
        Re: CRACKS!!!!Stress rising

        no blanket....it is a 3 piece dome. Had a few sticks in there, but was not to bad, sent the pictures to Forno bravo, they told me, and I quote..... "I had my production crew Look at your photos, and this type of crack is something that can happen on occasion with brick ovens due to the expansion and contraction that results from thermal cycling. But it will not cause you any problems, either with how well your oven cooks or on its long-term durability. You can continue using your oven and not worry about this. As far as the gap he said that is not abnormal and will not cause any problem what so ever. You can continue your curing it is not going to separate or damage the dome.", .........so I guess I keep going......So maybe I relax, have a cold one

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        • #5
          Re: CRACKS!!!!Stress rising

          I figure that if more ovens have cracks than not then it is probably abnormal not to have them. Provided of course that they stay within the realm of being cracks. Once smoke emanates from them then they become fissures and probably need some remedial action.

          Probably a bit like wrinkles, part of the character of what they appear on.

          I think the relaxed cold one sounds like the right strategy.
          Cheers ......... Steve

          Build Thread http://www.fornobravo.com/forum/f3/n...erg-19151.html

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          • #6
            Re: CRACKS!!!!Stress rising

            A monolithic cast dome shape is going to crack, period. Drink beer, fire it up and if bits start dropping off, hold Forno's feet to the fire.

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            • #7
              Re: CRACKS!!!!Stress rising

              I don't mean to be the worry wart here but that doesn't look like a stress crack. I looks to me like it has the potential to "pop" off. If no one breaks a tooth when it happens no worries. Even if is does drop, your oven will perform as hoped for many years. Have a cold one...
              Check out my pictures here:
              http://www.fornobravo.com/forum/f8/les-build-4207.html

              If at first you don't succeed... Skydiving isn't for you.

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              • #8
                Re: CRACKS!!!!Stress rising

                hey....thanks for the feed back. feeling a LITTLE better about it all. Kind of scary when you take a boo inside the oven and see that. still going at the cure(up to 3 sticks today)if I can get me to the 800f mark, with no more worries, I think I will be good. Going to have that "cold one" and relax. Also when I looked in it, it looked like a small piece was going to "pop off" as you mentioned Les, you still think all is good?? Man, that cold one is sounding better all the time!!!!cheers all

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                • #9
                  Re: CRACKS!!!!Stress rising

                  I build pizza ovens and outdoor kitchen for a living but I'm by no means a refractory engineer but I got a hunch that heat stress can crack an oven either by heating it to high at too fast a rate or cooling it at too fast of a rate especially considering there's still moisture in the casting.I think cooling an oven from 500* to room tempature in one hour may be as stressful as going room to 500 in one hour.A high wind or cold weather could make make this worse.Ill start a fire in them without the blanket to help release more water from the casting but I always throw a blanket on it before putting out the fire.But thats just redneck engineering and it seems to work for me.Years a go I use to weld huge gear hubs together on a sub arc machine on a huge positioner and if you don't preheat them pretty hot before welding the welds would crack from heat stress from heating to fast but by the same token If you didn't put ceramic insulation blankets over the gears as soon the welds were being made the weld would crack from cooling to fast.I belive Tscarbourgh use to or still does rep these materials(Refractory and masonary)maybe he can comment because I could be wrong as it pertains to refractory.

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                  • #10
                    Re: CRACKS!!!!Stress rising

                    I agree Txt, that's why I asked if it was cured with the blanket on or off. I believe it's not only the rapid rise and fall of the temp of the refractory that's important, but also the temperature differential between the inside surface and the outside surface which also leads to uneven expansion, stress and hence possible cracking. If the oven is heated and it's uninsulated, the ambient temperature fairly low, maybe some wind and the outside surface wet, this will be enough to hold down the temp of the outside surface lots. To be safe to the refractory the temperature riseor fall should not exceed 100C/ hr, but nobody firing a WFO does it this slowly.The highest quality refractory materials may still fail if heated or cooled too fast.
                    Last edited by david s; 08-01-2013, 02:54 AM.
                    Kindled with zeal and fired with passion.

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                    • #11
                      Re: CRACKS!!!!Stress rising

                      I get the rapid rise in temperature if you build a big fire.... But how can a Pizza Oven possibly cool from 500 degrees to room temperature in an hour?? Even without insulation my oven would take about half a day to cool to about 200. With insulation my oven takes days to cool down. So unless I am missing something it is only the heat cycle that is going to cause problem, not the cool cycle.

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                      • #12
                        Re: CRACKS!!!!Stress rising

                        Originally posted by boerwarrior View Post
                        I get the rapid rise in temperature if you build a big fire.... But how can a Pizza Oven possibly cool from 500 degrees to room temperature in an hour?? Even without insulation my oven would take about half a day to cool to about 200. With insulation my oven takes days to cool down. So unless I am missing something it is only the heat cycle that is going to cause problem, not the cool cycle.
                        A cast oven with thin walls will cool and heat faster than a brick oven, which has thick walls.. Maybe not 500 F in one hour, but if the refractory is wet, the ambient temp low, no door and some breeze over the dome, the fall in temp will be rapid.
                        Kindled with zeal and fired with passion.

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                        • #13
                          Re: CRACKS!!!!Stress rising

                          Doh! I totally missed that this was a cast oven. Sorry about that!

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                          • #14
                            Re: CRACKS!!!!Stress rising

                            Hey warrior no sweat,to tell the truth I pulled that "cool 500* in one hour "number out of thin air......or as we say down here"outtamyass".It was meant as an example,but I guarantee you it could happen and probably has.Follow along and see if you could see this happening.You(meaning anyone of us)has wanted their very own pizza oven in their very own back yard for two years so one day you say to your self damn it, I work hard,I'm a good father and husband that always puts my family's needs and wishes before my own.....so I'm gonna do it,I'm buying me a pizza oven no if ands or buts about it.So now you get on the computer and find a bunch a like minded pizza nuts and start asking questions and researching everything down to the last little detail all the while saving ever dime you can to fund this new addiction.No beer no cigarettes no eating out no golfing no movies no nothing.You sell the bass boat and put the checkbook on lock down and tell the the kids the only thing you're puttin out around here is the lights.By now the urge to call James and order 56 inches of Modena2G140 heaven is unbearable but you have one last hurdle,until now this has been a private addiction....yes it's time to tell the wife.All day at work you've been planning out what to say and how to say it,hell you even had flowers sent to her at her office.As you sit down to dinner you sum up the courage to speak in spite of the fact you know how bad this may turn out.Honey I've been thinking about how you say we have no social life and we never go anywhere or visit your family or your friends and dog gone it your right .........so that's why I've decided WE'RE GONNA GET A BRAND NEW HARLEY DAVIDSON .I got it picked out already and the best part is it's on sale for $28,000 and the dealer said he'll hold it for us till tomorrow morning plus I got enough cash saved to put half down so we'll get 0% financing.Well the next 2 hours is a blurr of insults and repressed anger as well as rehashing old arguments and a general stroll down the memory lane of discontentment.It is even made clear that you are entering the early stages of the middle age crazys and no doubt will be covered shortly in tattoos.Some how in all this it's decided the money would be better spent around the house so you give in as usual and unselfishly agree that a pizza over would be a nice compromise because ya'll can now socialize and have weekly pizza parties and invite the inlaws and her friends over as well as spending quality time together fixing up the backyard.When you suggest that you'll sleep on it tonight and decide what to do in the morning about the Harley she insist that the two of you get on the internet tonight and shop for a pizza oven and lawn furniture.Well somehow that night yall decide that the modena2g140 is perfect so its ordered and paid for in full......as a matter of fact she inscist on ordering and paying for all the materials needed for the whole project tonight,all $14,000 of your Harley down payment is gone and the night ends with her sweetly kissing you good night and telling you what a wonderful husband you are for giving up your Harley.

                            The next day you go right to work building your stand,the work is flowing smooth and every thing is going as planned.Saturday you form and pour your slab with great precision because you've done every step a million times in your head and are prepared for everything.Sunday you lay out your block for the stand and get everything precut and notched.You dry stack it on your drive way and its perfect.....damn your good.Monday after work you rush home and remove the plastic from your slab,knock off the forms and the slab turned out great....not a bit of porosity because you vibrated and screaded it to perfection.No time to pat yourself on the back yet,you start dry stacking your block on the slab and all goes smoothly.All the vertical rebar in the slab lines up perfect with the holes in the blocks and your flying. Steele lintel fits perfectly flush and everything checks out level plum and square on the fist try so you wast no time and start mixing rapid set concrete and back filling the blocks which goes just like you planed.While the concrete sets you start screwing your precut forms together for the supporting slab and by the time the quick set kicks off your pouring your hearth slab.It's 1 am and your exhausted but oh so satisfied and for the first time you know what it feels like to be"In the zone"Tuesday starts off with alot of coffee but you make it through the day but all you can think about is insulating that slab so as soon as you get home you change and hit the wheelbarrow and knock it out and it to just falls into place with no problems.you clean up and call the trucking company to confirm delivery and low and behold it's 2 days early....can you believe your good luck.They said they can drop it off thursday morning so you spend wednsday stuccoing the stand and taking care of any little details you can to move forward and prepare for arrival day and going over your list to make sure your prepared and you are prepared because you planned your work for a year.You wake up early Thursday and call your boss and tell him your taking off work because your kids are sick, he's really understanding and shows real concern for your kids well being so when you hang up you feel guilty about lying to such a nice guy so you wake up the kids and ask them if they're sick of school which of course they say yes so you tell them they have to stay home today.Your now guilt free so you head out back and check your list one last time but everything ready and you feel you really have thought this all through.Truck shows up at 8 sharp and you unload the crate onto special cart you made so you could wheel it in the back yard by yourself but the driver wants to help so It's in place and uncrated in 10 minutes flat.You thank him and offer to make him a pizza some day but he says ....no thanks I don't care for pizza except for Domino's.Obviously he doesn't get it so you ask him to leave so you can get to work.As you start you are amazed at how easily the oven goes together.It's hard to Know if it's your skill or just that you were so prepared for this moment.With your two boys trying to help you get it all set in less than two hours and you can't belive how smoothly the whole project has gone.You can't wait to start a fire but you know you must so you spend the rest of the day cleaning up and going over your paperwork and manuals to make sure you understand everything.Over the next week you do your curing fires every evening each one bigger and bigger.Today's the big day,not only is it May 31 which is your birthday but today you'll build your first full log fire. You start early building your fire and by 8 in the morning you have a big fire going and your just thrilled because up to this point everything has been perfect,the flue draws great and not a single crack so you go in the house for a cup of coffee.As your pouring a new cup you start to let your mind wonder and then you think you hear a strange noise but you don't know what it is.....chic.....chic .....chic....so you start heading to the back door and now it's louder....chic...chic...chic....What is that?You think to yourself that's familiar.....chic ....chic .......chic.....chic....OH NO!.......chic...chic.....chi.chi.chi.chi.chi.chi. chi.chi.chi.You run out the door but its to late,your ovens in pieces,your fires out and your automatic sprinklers are working great.Damn you didn't think about those because they're programmed off through winter,they're not programm

                            ed to come back
                            on until 8 a.m. May 31 of each and every year.Yes Sir on your birthday,you set the date ten years ago when you first bought the house.


                            See it could happen.

                            Bill
                            Last edited by TxTanner; 08-02-2013, 04:53 AM.

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                            • #15
                              Re: CRACKS!!!!Stress rising

                              Holy crap Bill thanks for making my day!! What a great story - you had me on the floor! My cubicle neighbor here at work wants to know what I am laughing at!!

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