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"Pompeii" corner WFBO project in Loei, Thailand

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  • #31
    After checking all the alignment, time to elevate the base for the IT (indispensable tool) and cut bricks.
    Click image for larger version

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    The top of each soldier was marked and cut for a 17* angle (6mm off the inside). The curve of the dome will start 11.5cm above the floor (half-way up the soldier bricks). If you've ever seen an observatory like the one at Mt. Palomar, there is a straight walled cylinder with a domed top. That is the intent of the full height soldier bricks. The curve of the dome will actually be measured half-way up the soldier bricks.

    The brick last soldier next to the form in the upper right of the picture above needed to be trimmed lengthwise. So...that revealed a fundamental flaw in the type of wet saw I have (as predicted earlier on this forum by, I think, @UtahBeehiver). I eventually made the cut, but it looked very rough. The wet saw did fine for part of it, but even at an angle it won't slide over the brick or cut deep enough. I think I have a better solution for this now. For this one, I used a 4" grinder to finally finish the cut. Keep in mind, wet saws are very rare in Thailand and there aren't many choices.

    Next I started pre-soaking the bricks and using mortar between them.
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    This refractory mortar seems very unusual to me. The mortar comes pre-mixed in a zip-tied bag placed in a 5 gallon black bucket. The instructions specifically state the mortar should be used on dry, clean bricks. Per other recommendations, I pre-soaked. I might try a test not pre-soaking to see how that acts. Another forum member, Vinz, recommended I mix in sand to make it "more like normal mortar." I tried mixing in sand, then sand and brick sand (recovered from wet saw). For me, both mixes made the mortar more difficult to use. The mortar acted like the opposite of a super-saturated solution (more dissolved matter than can be supported by liquid, slighted agitation results in a solid); if I let it stand, it acted kind of like warm butter. However, any agitation at all caused the mortar to liquify. I could place a scoop of the gelatin like mortar on a brick and immediately stand the brick on end without the mortar sliding off. However, if I combined two bricks, both with some mortar on the side, when the mortar met the whole mess liquified and fell all the way to the bottom.

    Next, I tried just the mortar. I mixed it (per instructions to "re-homogenize"), placed it on bricks and it would hold. Better yet, I could use a putty knife to wedge more mortar into the joins. With the sand, I had to let it dry significantly before I could do that. At least for me, this BST AM 30 pre-mixed refractory mortar is easiest to work with by itself.

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    You might notice in this picture a vertical crack. Contrary to instructions on the package, I did pre-soak all the bricks. I don't know if this is serious or superficial. I wedged the ones I found. I will test the joints for strength when I return next week.

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    Where I could with the mortar I had prepared, I covered the exterior (about 3/4's of the way) with mortar. I will find out if that helped or hurt next week.


    This brings me up through yesterday, Friday the 17th. I will return to do further work on the 25th or 26th.

    Comment


    • #32
      Thanks for keeping us posted, looking very good and professional!

      Also nice to see how the pre-work of the whole area was done.
      Funny to read about different behaviour of the same wet-type mortar on the same bricks and even in a pretty similar geographic location (other season, though ;-) )
      Wondering how the mortar will do after drying (if ever for real, prior to firing).
      The wet mortar on the soldier bricks, in my case, i would be able to peel/chip it off the next day.

      your prep-work and thinking it through is amazing. actually, i found the planning of this build a very enjoyable experience myself, as well as the knowledge I gathered about the materials involved

      Good to see those good old heavy BST bricks being used again!
      Regarding the cutting, I used an expensive diamond saw on one of these cheap Thai cutting tools (you got a picture of a guy using it to cut the rebar bars). Worked fine for the whole build, the blade is still good.

      I noticed that in the dry-build you sometimes have the print on the bricks towards the inside of the oven. Then in the real build, it does not seem to be the case. Just wanted you to make sure there is no print pointing inwards, as this looks rather unnatural when you look inside (and there will be a lot of looking inside when cooking time comes).

      Wetting the bricks for me was rather superficial, the BST bricks don't seem to soak up that much water. without the soaking, the bricks would draw the water out of the mortar way to fast, resulting in miniature cracks. At least for me at the time, now it looks like your mortar behaves totally different..
      Regarding floor insulation, you got a bit less than me (i have a full BST brick as base which is thicker). I found the base insulation to be the weakest point in my build in hindsight. Also rebar bars in my opinion might drain the heat. I have an open table as a base however, which might ventilate more heat than your pretty much enclosed base. Hope that will help.

      Looking forward to your next update!

      Comment


      • #33
        Just be aware that by raising the IT platform, the dome height will be higher than the dome width at the base by the amount raised unless you make adjustments accordingly. This may affect the arch opening golden ratio of 63 to 65% of the dome height.
        Russell
        Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

        Comment


        • #34
          There could be any number of reasons the mortar acted differently, especially my own inexperience. Since I have little masonry experience (plenty of watching, very little doing), I'm not really sure what mortar should act like. Accordingly, I might have found it easier as it was. Also, it's possible they changed the ratios/formula or one of us received old and one of us received new. This definitely goes on thinner than most mortar I've ever seen applied or in actual brick builds in Texas.

          At the moment, I am in Chiang Mai. I was able to find a 9" (230mm) diamond (dry) blade with a 20mm arbor that will fit my table saw. That should allow me to make the more complex cuts for the archway. Worse case, I can get a chop saw for around THB3500 in Loei.

          As UtahBeehiver suggested, I looked up the tapered arch on mrchipster thread (https://community.fornobravo.com/for...2-in-minnesota) and I think I know what I have to do for the arch starting at the corner. I'll probably have more questions when I get to that point.

          I am sure I will learn a great deal and some of it will be by making mistakes.

          Regarding the dome height, as I have it configured now, I think it is r55cm +11.5cm for a 66.5cm dome height. The inside arch height is 39cm (IIRC), making it 58.6%, so smaller than ideal. In reading through the forum threads, there were some (IIRC) with ratios even farther askew. I read some discussions about just how "golden" the ratio is in a practical sense. I don't know either way. If I put the IT at floor level, then it would be 70.9%. To achieve 63%, the IT should be 6.9cm above the floor (61.9cm dome height). In a sense, it's totally arbitrary. The "wood brick" is sitting on blocks to raise it as high as it is (actually, I think it is still a little low). In 15 seconds, I could lower it ~6cm. As I haven't started to place the second course yet, no rework is required. This doesn't even affect the cut on the top of the soldier bricks in a meaningful way.

          How critical do you think the 63% ratio is and how precise does it need to be?

          Thanks for the timely feedback. I can easily address this now. Later it will be impossible.

          Comment


          • #35
            It is a 63-65% arch height to dome height is rule of thumb that provides the best effeciency of oven performance and venting. Are there exceptions, yes but if it only takes 15 seconds to lower, why not? As for the tapered inner arch, you start with full length bricks at the top dead center(TDC) of the arch (also the longest of the arch bricks) then work your way down each side of TDC using a combination of the IT for top slope and the previous brick cuts IE, looking from the inside of the dome outward, the left side of the TDC will be the pattern for the right side of the next brick left of TDC and visa versa for the right side of the TDC. Each brick is unique so you cannot cut the arch bricks all the same, they are not all the same in shape.
            Last edited by UtahBeehiver; 01-20-2020, 07:22 PM. Reason: fat fingers
            Russell
            Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

            Comment


            • #36
              So, I was gone for 7 days and only finished mortaring the soldiers in place. As per the pics I saw from others, I took the excess mortar and simply added a layer around the backsides of the bricks on half of the bricks. This did not work well.

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              This side I covered after it already started to dry. The bricks were soaked and removed 2-4 at a time. Then I put mortar on each side and placed the brick. Again, at 2-4 at a time, I filled gaps and packed more mortar in the gaps. On this side, I went back about 90 minutes later and slathered on additional mortar over the exterior. I also covered the ceramic fiber board and oven floor bricks (notice that didn't crack). I then placed a tarp over the project to prevent direct sunlight.

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              This is the opposite extreme from above; this is where I finished last Friday. I didn't have enough open mortar to go over this other than to kind of fill the gaps. Obviously, there is far less cracking.

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              This is the transition area where I ran out of excess mortar to go over the exterior.

              Any thoughts?

              Did it dry too quickly? I've seen people all my life spray down curing concrete to prevent it from curing too quickly. Should I have arranged to spray it down?

              The instructions for this mortar clearly state the bricks should be dry. All the advice in the forum and on the FornoBravo plans say soak the bricks. Since the part that didn't crack was where I covered the oven floor and ceramic fiber board, does this mean for this mortar, dry is the right method?

              Is it even fully cured yet? Looking at the second picture, I think the thick areas are still wet inside. If true, I think that supports the idea I need to stick around and spray water on the mortar to prevent it from drying too quickly.

              Whatever did stick was enough -- the bricks are locked in solid -- they are not moving without a sledgehammer. I am not overly worried. If they were loose, or easily broke apart, I'd be very concerned. The joints on the inside are near zero gap. The exterior will all be covered.

              Subject to suggestions, I am leaning toward trying dry brick on several bricks and spraying down soaked bricks on several others. The challenge is the next part will be visible because I have to do the columns for the arches. So, again subject to suggestions here, I will do the inner arch columns, then start on the second course of bricks, doing one side dry, one side pre-soaked. I'll only do a few of the second course bricks and will keep one side moist.

              Any advice will be cheerfully appreciated.


              Comment


              • #37
                I found a happy medium when wetting the bricks, a light spray or dip prior, seemed to work ok.

                I didnt have flaky mortar like that though, what fire mortar mix are you using ? Perhaps one for Russell.

                As i learned on this forum, you wont see the back end of any bricks - its all about the inside.
                My Build

                https://community.fornobravo.com/for...r-build-darwin

                Comment


                • #38
                  I need to update the thread. I mortared in the inner arch columns and transition bricks from the soldiers to the columns. I went back over much of the brick I cleaned up.

                  The new work turned out pretty good. The lines are much thinner -- I think that is critical with this mortar. I also put wet rags over the work and I think that helped a lot. In the pics above, even after a week, they look partially wet. I think they were. The new stuff dried much faster -- that is reached a light gray color -- and there were no cracks in the new work. Where I did some rework, there were some cracks, but much smaller.

                  I am using a refractory mortar sold in Thailand by BTS called AM 30. It is pre-mixed and comes in sealed 5 gallon buckets. The instructions say remix to ensure it is homogenous, then apply to clean, dry bricks.

                  The bricks I used for the new work were slightly moist or dry. Some of them I had just cut with the wet saw, but they had been sitting for a little while. Others were dry. None of them were soaking, like the first bricks I did.

                  I had to drive my cat to the hospital in Bangkok. So I should be able to return to it by the end of the week.

                  Comment


                  • #39
                    I think your correct about keeping it moist for as long as possible. The slower it cures the better.

                    As for the brew, perhaps take a pic of the AM 30 contents/ratios, and post back for others to comment. I used the standard 3:1:1:1 and had no issues, except for average masonry skills of course
                    My Build

                    https://community.fornobravo.com/for...r-build-darwin

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                    • #40
                      I asked them for the data sheet and they sent me a link (pic below). I had seen it before, but was primarily looking at the components. The way I read it now, this mortar is meant to be heated to cure, or at the very least, full strength is achieved after heating.

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                      Here is the data on the brick. The brick I have is SK30, the first column.
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                      Attached Files

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                      • #41
                        Spot on. Hopefully david s or someone can comment on how best to apply it.
                        My Build

                        https://community.fornobravo.com/for...r-build-darwin

                        Comment


                        • #42
                          You are wasting your money buying a mortar that contains high temperature aggregates that your oven does not require. You also won’t get it to the temperate required for it to sinter. The homebrew is a far better mortar for ovens. As the data shows the high duty bricks are way harder and will be a bitch to cut. Medium or low duty are more suitable for the dome. Medium duty for the floor.
                          Last edited by david s; 02-05-2020, 12:16 PM.
                          Kindled with zeal and fired with passion.

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                          • #43
                            Choices of materials in Thailand are very limited. Communication difficulties further hamper our ability to explain what we want to the very few people who might have any knowledge of specialty building materials.

                            I've not had difficulty cutting the bricks. The wet saw works fine. There were some cuts where I had to use a dry blade on a table saw (the wet saw is an overhead unit with insufficient clearance for the brick on its edge. At first, I found these cuts nearly impossible. Per some comments in other threads, I used a sprayer to keep down the dust. The bricks were getting extremely hot. I switched back to the 9" blade from the 10" blade thinking that might help. Partially out of frustration, I doused one of the bricks. When I started to cut again, there was no more chipping, the cut was very fast (faster than the wet saw), and the cut was extremely smooth. The down side was this created huge amounts of dust and frosted a pair of goggles (I was wearing a breathing mask, leather sleeves, gloves...whole PPE kit). I switched back to the 10" blade and finished the inner arch bricks in about 30 minutes. The measuring and marking took longer.

                            Where I've used the mortar, it seems very solid. If a gap was small, say 2-5mm, there were no cracks. Larger gaps tended to crack with very large gaps developing large cracks. The angled joints I've made since my first use of the mortar, I've inserted wedges of brick. This seems to work very well. The even joints look fine. This has meant I have to do much more cutting to try to minimize angled gaps, slowing me down considerably. As I wrote in an earlier post, placing wet towels over mortared joints and leaving the bricks dry seems to have helped too.

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                            • #44
                              Frequently, I hear comments like "making mistakes is how we learn." Well, I've been doing a lot of learning.

                              Per an earlier suggestion, I angled the top of the soldier bricks. Unfortunately, the angle was far too shallow (miscommunication between myself and the person doing the drafting). My first thought was I could correct the angle using a 7" hand-held grinder. I marked the brick and started to make a cut (red line in pic). I quickly realized once the blade sank into the brick, I couldn't see to control the angle of the cut. I quickly halted that test.

                              My next attempted solution was to create a transition wedge (green triangle). Unlike the soldier bricks, they are angled on the sides to eliminate gaps. When I dry fit them against the IT, I found the wedge was not really thick enough. I am not sure if I can make this up with mortar or if I will have to put in other, thinner wedges. I prefer not to do the later as the result will probably be very uneven.

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                              I then made a mistake in cutting the arch bricks (another miscommunication). As I explained in an earlier post, in order to cut an angle on the length of a brick, I needed to use a table saw with dry masonry blade. At first this was extremely difficult, resulting in very rough cuts and lots of chipping. Per comments on other threads, I tried spraying the bricks with mist to cut down on dust and cool the bricks. Out of frustration, I doused one brick. When I started to cut again, the blade went through the brick very quickly. The cuts were smooth, even, and there was almost no chipping. New process was the soak the bricks before cutting.

                              After cutting the arch bricks, I did a dry fit and discovered they were far too angled. This was a huge mistake costing me at least 12 bricks. I am hopeful I can use them later in the dome.
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                              Instead of using the CAD drawing, I calculated the inner and outer circumference of a circle of bricks, the number of bricks required, and then how much narrower the inner edge of each brick needed to be. Then I cut new bricks.
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                              These are just the side angle cuts. I still need to mark and cut the taper on the inside.

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