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Mongo's 42" CT Build

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  • mongota
    replied
    Originally posted by Gulf View Post
    Great job! You're a very fast worker.
    It's been a good productive week, Joe. I'm glad to be back at it.

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  • mongota
    replied
    Second coat of stucco:

    Used the same 3:1:1/2 mix as I did for the first coat.

    I'll let this set up, then I'll mist it for several days as it cures. My plan is to eventually coat it with Thoroseal for waterproofing and then cover the shell with a stone dome. I prefer the Thoroseal as it's a cement-based product. I'll be be gone for a few days so that'll give the shell about a week of curing before I do the Thoroseal.

    Not much to do now except let the shell cure!


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  • Gulf
    replied
    Great job! You're a very fast worker.

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  • mongota
    replied
    Stucco coat #1:

    This went on well. The nice thing about working over a slab is that any dropped material was easy to get back on the dome. Pretty much zero waste. After the coat was done, I forgot about combing it out to give some tooth for the second coat. By the time I did think about it, if I'd tried to comb it out I probably would have simply sheared it apart. So I did some half-hearted dimpling with the notched side of one of my trowels. lol

    Where the dome meets the hearth, you can see the bright red ring of the RedGard I applied over both the tapcons and the 1/2" lath return. That was done prior to the stucco.

    Nothing fancy with the stucco, a 3:1:1/2 mix. I used about 50 lbs of portland, one wheelbarrow load of mix gave enough to work it into the diamond mesh and fully encase the lath. I was shooting for about a 3/8" to 1/2" thick layer.

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  • mongota
    replied
    Originally posted by Gulf View Post
    I found that galvanized hardware cloth was easier to fit to the compound curve. But, after seeing your insulation fitting, I don't believe that you will have a problem with either.
    The lath, being an expanded diamond lath? I had considered stretching and shaping it prior to installation to get it to conform to the curve of the dome. But then I decided to stop thinking and just start working. I do think too much at times. lol

    I do have hardware cloth, that would have been much easier to tie together. But for the stucco coats to follow, this time around I preferred the diamond lath.

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  • mongota
    replied
    The lath went on well, but it was a bit of effort tying it together with rebar wire ties.

    The lath I used comes in roughly 2' by 8' long pieces. I used the edge of a table to bend a 1/2" 90-degree return along the 8' length of the lath. I stood the lath on that return and then wrapped it around the circumference of the dome. I ran tapcons through the 1/2" return to secure the lath to the hearth slab. After securing, I had a little bit of RedGard left in the bucket from way back when, so I used RedGard to seal the tapcons, to "paint" over the return of the lathe, and I brushed more on the hearth slab to extend the ring of RedGard waterproofing out from the lath another couple of inches.

    With a cylinder of lath wrapped around the half-sphere of the dome, I used an angle grinder to vertically slice the lathe so it could conform to the curvature of the dome.

    I used 6" rebar wire ties to stitch it all together.

    Not shown in the photos, but I added a second layer of lathe on the lower part of the dome where the cut lath abuts and doesn't overlap. That should help minimize stucco cracks in those areas.

    In one of those really weird serendipitous moments, I had maybe 1-3/4 packs of 6" wire ties that I bought when I started building the oven. I used them up, and was going to have to run out to get more. I went in my basement and found the remnants of a REALLY old package of wire ties. They had to be 20 years old from when I built the house. There were maybe two dozen wire ties in that package, covered with surface rust, and that was exactly the number I needed to finish stitching together the lath.

    Perfect.

    And I have to say, the older ties were much better to use than the newer ties. The new ones would snap if you sneezed at them. The old rusty ones, I could snug them tight and not one snap.

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  • mongota
    replied
    Originally posted by MichaelPBoisvert View Post

    How many rolls of fiber blanket did you end up using? Are they 25' rolls?
    Michael, I used roughly 3-1/4 rolls, the rolls were 8# density, 2' x 25', 50sqft per roll.

    When it came time to calculate the amount of insulation needed I had a 21" interior radius dome, but that dome was sitting on top of a 4" thickness of board insulation and a 2-1/4" thick floor brick.

    So to calculate the surface area of my dome, I used the vertical radius of my dome versus the horizontal radius. From the slab the dome is built on measuring vertical, I calculated the radius by adding 4" of board insulation + 2-1/4" floor brick thickness + 21" interior dome radius + 4-1/2" dome wall thickness + 2", with that 2" simply being a point 50% of the way through the thickness of the eventual blanket insulation. A total radius of 33-3/4", which gives a surface area of 50sqft.

    I knew going in that the 50sqft number was a generous number, because my first layer was going to sit on top of the 4" of board insulation, plus there was the vent arch which took away from the surface area of the dome that I needed to cover. And my dome doesn't honestly have a 33-3/4" radius. Geometrically, it's less than that as it's more like a half-sphere sitting on a section of cylinder.

    So I bought four boxes, a total of 200sqft, and used roughly 3-1/4 to 3-1/3 boxes. I used the wedge-shaped off-cuts from covering the dome to cover the vent arch. They all knit together quite well.



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  • Gulf
    replied
    I found that galvanized hardware cloth was easier to fit to the compound curve. But, after seeing your insulation fitting, I don't believe that you will have a problem with either.

    Leave a comment:


  • mongota
    replied
    Thanks, Joe.
    I'll get some lath and possibly some stucco pics up in a few hours.

    Leave a comment:


  • MichaelPBoisvert
    replied
    Originally posted by mongota View Post
    Dome insulation. With 4" of rigid board insulation under the dome, I wanted 4" on top of the dome as well. Used four layers of 1" 8# ceramic fiber blanket.

    The bottom edge of the first layer sits on top of the board insulation, the other three extend all the way to the slab. The slab has RedGard on it to prevent the blanket from wicking moisture through the slab. I sliced and butt-seamed my layers, instead of just overlapping everything, and offset the seams as the layers went on. It was easy to do and allowed the insulation as a whole to remain smooth as a whole and maintain the half-sphere shape.

    While I put four inches of blanket on the dome, I only put two inches on the vent arch. I considered putting none and I considered putting four. Compromise! lol
    How many rolls of fiber blanket did you end up using? Are they 25' rolls?

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  • Gulf
    replied
    Mongo,

    That is the best insulation job that I have seen. Great job!

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  • mongota
    replied
    Dome insulation. With 4" of rigid board insulation under the dome, I wanted 4" on top of the dome as well. Used four layers of 1" 8# ceramic fiber blanket.

    The bottom edge of the first layer sits on top of the board insulation, the other three extend all the way to the slab. The slab has RedGard on it to prevent the blanket from wicking moisture through the slab. I sliced and butt-seamed my layers, instead of just overlapping everything, and offset the seams as the layers went on. It was easy to do and allowed the insulation as a whole to remain smooth as a whole and maintain the half-sphere shape.

    While I put four inches of blanket on the dome, I only put two inches on the vent arch. I considered putting none and I considered putting four. Compromise! lol

    Leave a comment:


  • mongota
    replied
    Thanks Dan. The form really did simplify it. Nothing much easier than mortaring bricks together on the workbench and using the form to assure that they are indeed in plane with one another, and then carrying them outside to install as a unit.

    Small victories! I'll take efficiencies when and where I can, lol.

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  • WarEagle90
    replied
    Anchor plate turned out quite nice, Mongo. I like the use of the form to lay all 12 bricks at once. I can see where that prevented a lot of headaches with other bricks moving around.

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  • mongota
    replied
    With the bricks still in the form, I dry fit the chimney anchor plate in place and marked and drilled holes for the anchor bolts that will secure the anchor plate to the brick.

    I unscrewed the form and removed the two sets of brick, then I mortared the top of the arch as well as the undersides and ends of the left and right sets of brick, and set them into place. A few taps with my persuader to assure all was level and aligned, and all was good.

    I then screwed the wood frame back around the 12 bricks to hold them secure while the mortar cured. I had to slip the form up a bit so it could clear the curve of the dome.

    I used a tube of RTV and slathered it on top of the 12 bricks, then pressed the anchor plate into the RTV. I set the four anchor bolts and called it good to go.

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