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  • #16
    Re: spalling hearth

    "one easy hit it split in two quite cleanly"

    One measure. A standard brick should weigh about 9 pounds.

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    • #17
      Re: spalling hearth

      I just weighed one which came in at about 6.5#. It's an 8.5" x 2.5" x 4.25" (more or less) brick.

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      • #18
        Re: spalling hearth

        That looks like heat spalling to me. Note that spalling is more a function of heat differential than it is too much heat. Too much heat will cause it to crumble, while a heat differential will almost always cause concave spalls like yours.

        My guess is you had a good amount of heat in the bricks then cooled the surface rapidly enough to cause spalling.

        It could also be caused by an extremely cold oven being heated up too quick, although I would say that is more likely on the dome than the floor.

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        • #19
          Re: spalling hearth

          Kim,
          From a size and weight perspective, your bricks sound the same as my. Size is the same, the weight of mine are around 6 lbs 2-3 ozs. I used light duty "fireplace" firebrick. (yes, a data sheet was provided when I purchased them, so I am pretty certain of what they are)
          For the record, I just came from my garage where I measured and weighed a leftover as well as a "fired" brick paver I will soon be using to update the fascia on my oven. Both bricks probably have zero moisture in them (the firebrick has been sitting high and dry for 3 yrs, the paver - 4 months)

          I would say weight only matters when trying to determine what type of firebrick you have, not IF it may be a firebrick. The clay pavers that I have look identicle on the outside as my firebrick, only difference in appearance is the color. The paver is the same width and thickness, but 1" shorter (7 1/2"), and weighs 5 lbs 9 ozs., Damn near the same as the firebrick.
          I'm certain the weight rule matters when comparing types - insulating firebrick usually run 2.5 - 3 lbs., light duty= 6 -7 lbs., medium = 8 - 8.5, and heavy duty = 9+ lbs.

          Just thought I would throw this info out there...food for thought

          RT

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          • #20
            Re: spalling hearth

            I think what I'll do is go ahead and flip the ones I have in place right now and just be more cautious about firing when the hearth might be wet, and to be cautious about the mopping when baking bread. Even if the brick are not refractory, which I don't believe is the case, and they spall even with the precautions, then I'll just re-do the removal and assure I have the right brick. I'll keep you posted on the progress. All in all, it's really an inconvenience at this point. I mean to bake some bread tomorrow anyway and will slate a time for repairs when I don't plan on any baking.
            Thanks all. Ain't this great?

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            • #21
              Re: spalling hearth

              "Even if the brick are not refractory, which I don't believe is the case,"

              I am not doubting you, I was just raised the possibility because this type of spalling is definably unusual.
              Last edited by Neil2; 06-05-2010, 04:32 PM.

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              • #22
                Re: spalling hearth

                No worries, Neil. It's always a good thing to question and investigate. I appreciate all your input. Everyone's.
                Kim

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                • #23
                  Re: spalling hearth

                  Originally posted by Neil2 View Post
                  "Even if the brick are not refractory, which I don't believe is the case,"

                  I am not doubting you, I was just raised the possibility because this type of spalling is defiantly unusual.
                  I've been following this thread for quite some time and I have to agree with Neil. It is very unusual for refractory brick to act in this manner. In the pizzeria I used to work at, we would cook a number of things in the oven. Sometimes if not frequently stews and boiled potatoes/vegetables would boil over and liquid would hit the floor. Mind you the cooking floor has suffered different types of abuse and not to mention constant cleaning with a wet rag. Never has it chipped or spalled in its 9 (going on ten) years of operation. Therefore, I can only think of two reasons on why the brick has degraded in this manner.

                  1. If you live in cold climate, liquid or any type of moisture from the food or other source has penetrated the surface of the brick and has frozen causing the spalling.

                  2. You were sold inferior manufactured brick. This is easier to test by buying brick from another supplier to replace the ruined bricks.

                  Hope this helps.

                  Yours truly,
                  Raffy
                  Last edited by Raffy; 04-28-2010, 07:07 PM.
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                  • #24
                    Re: spalling hearth

                    Just an update: I finally got around to replacing the damaged bricks. Getting them out was easy, done as suggested above. I had a layer of sand mixed with fire-clay under the bricks and some of this had stuck to the removed bricks. So I scraped it off and saved it. But I had a lot left over even after making sure all bricks were level and flush.I had several bricks left unused from when I purchased my brick, so they came from the same lot - or close to it. But when I replaced the older bricks, size was an issue somehow. Nice sized gaping all over. I tried switching bricks to compensate for a lack of uniformity in manufacturing but that was a dead end, nightmare, useless endeavor. Everything is back in place now but, as I said, there are gaps bigger than I ever had. Not cast, but I could probably get a pencil in a couple of them. I'm not overly worried though.
                    The only draw back I can see is that one or two spalled bricks are the ones underneath the soldier course so they remain. Fortunately, these are on the perimeter and won't be a huge issue, if at all.
                    As always and ever, I want to thank you all for your input and passion. I tell people I built this oven all by myself in that I was the only person to so much as lift a tool or a brick. But I was helped by good people all over the planet. And that feels like a good connection.
                    Ain't Life grand!
                    Thanks,
                    Kim

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                    • #25
                      Re: spalling hearth

                      I do have a question, though, about those gaps. It's as though the bricks I took out had shrunk and so the areas where I put the new ones were bigger than they were when those bricks were new. I don't actually believe the bricks shrunk, just that it seems that way. Each brick I took out was, of course, the same size as the ones I put back in. But they didn't really fit the same. All I can think of is that due to the irregularity of bricks, their inconsistent measurements from one brick to the next, just means that I likely would not ever get new ones to match old ones anyway.

                      So, with these gaps and the fact that I'm not mortaring them in place, is there anything to be concerned about? Such as their being loose and becoming wobbly and moving as I bake? Or will heat and ash eventually "cement" them in place?
                      Thanks,
                      Kim

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                      • #26
                        Re: spalling hearth

                        I can assure you the brick dd not shrink. Possibly the ones in the floor expanded, the gaps filled with ash, and when you removed the spalled brick it left a slightly larger opening. So long as you bed the new brick in they should be fine.

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                        • #27
                          Re: spalling hearth

                          Oh, I know they didn't shrink. It just looked that way. What do you mean by "bed the new brick?" I just took up old ones and replaced them with new.

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                          • #28
                            Re: spalling hearth

                            What did you use to lay them originally?

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                            • #29
                              Re: spalling hearth

                              I haave a bed of sand mixed with fire clay that I had mixed with water to even out the surface. It was that mixture that was clinging to the bricks I removed. I scraped off that and used it as a dry bedding.I wasn't sure if I should wet it again so I didn't. I had a bit left over too. Still, everything is flush and level with all other bricks.
                              Thanks

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                              • #30
                                This is an old thread, so I hope someone will still respond.

                                I have a professionally built oven (inside dimensions 4.5x3 ft or about 1.5x1 m.) that I use in a home based baking business. I've been using it for about 3 years and the hearth bricks are beginning to crack and spall, some of them rather seriously. (I did see in one of the earlier posts here that someone made a distinction between spalling and crumbling. I would say crumbling is a better description of the hearth in some places).

                                While the mason had some criticism of the way the fire bricks were cut (i.e. not perfectly square), he didn't seem to have any concerns about their density or quality, so I don't think this is a materials problem.

                                The oven is housed in a building, and I live in a fairly moderate climate, but in the winter I bake only once a week, so I am often starting with a relatively cool oven. The oven was properly cured before the first firing when it was built.

                                When I fire the oven I build a lattice of sawmill slabs and other mill scraps(fir and cedar) that completely fills the oven, when these have burned down I use cord wood to keep the fire going (mostly fir and some arbutus [madrone to Americans] if I can get it) . Completely heat-soaking the masonry takes 7-8 hours if I'm starting cold. At this point the surface temperature at the back of the oven exceeds 900 deg. F.--the limit of my laser thermometer, so I don't know how much hotter. When the surface temperature has equalized and cooled to baking temperature and the ash raked out I swab the hearth with a damp mop.

                                So here are my questions:

                                Am I building a fire that's too hot too soon for a cold oven? Should some variant of the curing process be used to gradually preheat the oven before filling the whole oven with fire? Or perhaps a pre-firing the night before baking?

                                Could the problem be caused by wood that isn't completely dry?

                                Is it necessary to get the surface temperature that hot in order to soak the masonry, or is the elapsed time the more important factor? That is, can I achieve the same result by burning for the same amount of time but at a lower temperature?

                                What's the best approach to repairing the existing damage? Should I remove and replace the bricks as described in some of the earlier posts here, or can the damaged areas be patched with some material that can be spread on? The local mason (not the one who built the oven) suggested something, but, sorry, I can't remember the name of it right now, and I don't know if it would be food safe.

                                Any suggests about either causes of the problem or remedies?

                                Dana

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