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Freddie's Fun Dome - Forno Bravo Forum: The Wood-Fired Oven Community



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Freddie's Fun Dome

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  • Freddie's Fun Dome

    Actually, it's not a dome yet and I'm certainly not having fun with it tonight.

    Four days ago I set my soldier course into place. I'm using the FB high heat mortar. I soaked the bricks before setting them into place. I mixed the mortar to peanut butter consistency, buttered the bricks in a wedge shape to fit the seam between each brick then used one of those cake icing type bags to squeeze extra mortar into the gaps between each brick. Since then I've kept the bricks covered with a tarp.

    Tonight I took off the tarp to admire my work. While checking the seams I gave one of the bricks a slight tug and the seam between that brick and the next broke loose. In a state of shock and panic I checked a few more seams and ended up breaking five seams before coming to my senses and stopping.

    Between each broken seam the mortar was stuck to one brick and cleanly broken off the other brick. Where the mortar had been on the brick was still damp and the mortar was also damp where it had separated.

    I chipped the mortar off the brick it had adhered to, put the brick sections back into place, mixed up a new batch of mortar and used that bag to squeeze new mortar between the bricks. I couldn't wet the bricks before applying the new mortar, but they still felt and looked a little damp.

    Can anyone help me with this? I figure after four days the mortar should have set strong enough to hold and a slight tug shouldn't have broken them apart. Am I doing something seriously wrong (possibly), was I just stupid to give them a tug (possibly), or am I just stronger than I realize (unlikely)?

    I was planning on laying the next course tomorrow, but Iím not sure if thatís such a good idea right now. How long do I need to wait between setting some bricks before I can lay the next course? Do I need to completely take apart my soldier course and start over?


  • #2
    Re: Freddie's Fun Dome

    I’ve been giving this mortar problem a lot of thought and came up with a possible cause. As I mentioned earlier, I soaked the bricks then covered them with a tarp for four days. When the seams broke the mortar and brick still looked and felt damp. Is it possible that the tarp held the moisture inside and the mortar still had not cured enough to hold?


    • #3
      Re: Freddie's Fun Dome

      Yow, Freddie, that's aweful . It would really bum me out too cuz those soldiers eat up a lot of that expensive FB Mortar. That happened to me about 5 times on upper bricks, mostly the arch walls or arch bricks, BUT it happened within minutes to 1/2 hour. I thought at the time, my mix and bricks were too wet and I did not let them hold long enough to dry up before I moved them or gravity moved them.

      Most of the time, the FB Refmix stuff is SERIOUSLY STRONG. Usually, it dries fast and hard. Keep soaking your bricks in water, maybe make your Refmix a little dryer though. It sounds like you did too good a job of keeping everything damp. Remember, the FB mix is NOT concrete and does not cure like you expect and want cement to do. It is a refectory mortar with Alumina and silica and fire clay. It should dry hard and not really have to cure.

      If you're having 100 deg weather, ya put a tarp on it but maybe remove it in the evening or just use a spray bottle to keep it moist for a few hours then let it dry. Also, if you are using a pastry bag then that too tells me your mix might be a bit too wet since you need it wet to force it out of the bag. Work at it more, it might be harder with a dryer mix but your wet bricks should make for a strong bond.
      Again, I feel for you scraping off the Refmix but I bet you wont have that problem again and it will be fun, trust me. Good luck - Dino
      "Life is a banquet and most poor sons-of-bitches are starving to death." -Auntie Mame

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      • #4
        Re: Freddie's Fun Dome

        Portland based mortars set by curing. Lots of water is need for this curing process).

        Refractory mortars set by drying. Slow drying is best - keep covered but don't add additional water. Full strength in refractory mortars is only achieved after firing at temperatures high enough to drive out residual moisture.

        I think you are OK and your mortar will set up after a while (unless you keep pulling the bricks out).
        Last edited by Neil2; 08-27-2009, 03:18 PM.


        • #5
          Re: Freddie's Fun Dome

          Dino and Neil - thanks for the input. I'll keep the ones that I didn't pull on in place and hope that they will set strong enough to hold the dome. As I mentioned above, I soaked the brick and they were still wet when I applied the mortar. Guess I took this wet thing too far. That's good to know that mortar sets differently than cement. I thought it all worked the same.

          I took some pictures last night and will post them later. You'll notice that the brick and mortar are still damp - and that's after four days.



          • #6
            Re: Freddie's Fun Dome

            The soldier course finally set and none of the pieces are not coming loose. Thanks for the help with that. I ended up mixing it much thicker than I had been and had to use a spray bottle to wet the bricks since I couldnít put large sections of brick already mortared together into a bucket of water. I kept thinking that it was too thick, but it held. Another part of the problem could have been the heat. Last week when I set them the first time it was 103 degrees. The oven is going in the corner of the yard surrounded by white vinyl fence, which reflects and seems to amplify the heat. It may have been even hotter where I was working. Yesterday was only five degrees cooler, but at least they held.

            Iím now starting on the dome. Iíve been debating building a parabola shape, an ellipse, a true semi-circular, or as Dino put it, a semi-circle with a squished top. I think Iíve come up with a good compromise between all of these. In a previous post about this Neil said that if building a parabolic shape, the dome height should be 85 to 90% of the radius. For my 39" inch oven that would be 17.5Ē max.

            To get the shape I went with a semi-circle, but rather than setting the focal point of the circle right on the dome floor, I dropped it a couple of inches below the floor. I adjusted the focal point up and down until I found the spot where the semi-circle would hit right on the soldier course, and the top of the semi-circle is 17.5Ē above the floor. This gives me a semi-circle shape, with the angle between each course being the same, and it keeps the top of the dome a bit lower.

            It looks good on paper, but I need to make sure it actually works. If I stick with this design the angle between each course will be 10 degrees. Iím wondering if this is too much of an angle for the mortar to hold.



            • #7
              Re: Freddie's Fun Dome

              I used an ellipse:

              Ellipses Calculator


              • #8
                Re: Freddie's Fun Dome

                I am still striking out on my mortar work. Yesterday I set three bricks of my first course above the soldier bricks. I mixed three small batches of the F.B. mortar - one pretty dry, one fairly moist, and one in between the two. Today when I checked the three bricks the one set on the medium consistency mortar had not set at all. That brick was just sitting on top of the mortar and did not stick at all. The other two bricks were set and holding.

                The mortar that was under the brick that did not stick was stuck to the top of the soldier brick so I got out a thin putty knife and tried to pry it off. In the process of doing that I again started knocking loose several of the soldier bricks.

                I am now back where I started - a soldier course that keeps breaking apart. I've tried wet brick, dry brick, wet mortar, and dry mortar. I haven't found the right combination that works.

                Any suggestions on what else I can try? Should I add something to the mortar to get it to stick to the brick better? Should I use my grinder to rough up the bricks before placing the mortar so that it could grab onto the brick better? I need to get this figured out before I run out of mortar. I've gone thru almost all of my first bag of mortar and am getting pretty discouraged with this step of the build.

                Thanks for any suggestions.



                • #9
                  Re: Freddie's Fun Dome

                  Something's really wrong. Have you talked to Forno Bravo? I haven't used used the forno bravo mortar, but you shouldn't be having these problems. Have you talked to them?
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                  • #10
                    Re: Freddie's Fun Dome

                    I sent them an e-mail today but figure with the holiday weekend they won't be in until Tuesday.


                    • #11
                      Re: Freddie's Fun Dome

                      I did notice that the extremely flat surface of the firebrick did not adhere sometimes.

                      I did not use fornobravo mortar, but the 'homebrew' fireclay mix. I found it to be extremely tenacious, sticky and smooth mortar. ( 3:2:1:1/2 fine sand,fireclay, portland,lime)

                      The other thing I did was cut my bricks with a chisel, and make each one wedge shape. It's easier than it sounds, believe me. The rough edge actually holds mortar and locks together tighter than heck!

                      Good luck..

                      This may not be my last wood oven...


                      • #12
                        Re: Freddie's Fun Dome

                        I think the mystery about my mortar not sticking to the brick may have been solved. This morning I was talking to a friend who is also building a brick oven and told him about my frustrations with the seams not holding. He told me that he purchased some F.B. Refmix and that I could try some of his.

                        The stuff I've been using came with the Pompeii 110 kit I purchased. My mortar was packaged in nylon woven type bags with no labeling. My friend's bags were labeled "Refmix" just like shown in the pictures. When we compared his mortar to mine his is gray and gritty. Mine is light brown and the texture of flour or powdered sugar. When I saw this it dawned on me that I was probably sent three bags of fireclay rather than Refmix.

                        Being that I've never done this before I didn't know what the Refmix was supposed to look like. When I opened my bag I assumed that the different texture was because it is high heat mortar and thus a completely different composition than regular mortar.

                        Tomorrow I'll call FB and check with them. However, after comparing what I should have received vs. what was actually sent has me convinced that I've been trying to put my oven together with fireclay.

                        NO WONDER IT HASN'T BEEN HOLDING!


                        • #13
                          Re: Freddie's Fun Dome

                          Hey Freddie,

                          Its possible they sent you the wrong stuff,,,But Im sure they will correct the situation, and dont let it get you down,,, As Im sure everyone else here will testify we all had some sort of an issue along the build BUT<< we will all also tell you it was still well worth it in the end.....

                          Keep Building



                          • #14
                            Re: Freddie's Fun Dome

                            Well, at least you can make a ton of homebrew with all that fireclay. ;-)

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                            • #15
                              Re: Freddie's Fun Dome

                              That's got to be frustrating. But at least you appear to have solved the conundrum.


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