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  • #16
    I'm able to source a couple of insulating options for under the oven. I've attached the PDFs for what is available locally and highlighted the ones that they have in stock (HD board + K-23 & K-25). Hopefully these load correctly. I'd appreciate the expert's opinions on the pro's and con's of the three choices available. MORGAN Board Products TDS.pdf Morgan IFB Datasheet.pdf

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    • #17
      With all my tools in hand, materials finally located and ready to purchase, and my paper design hopefully complete, I thought I would post again and run some design and construction issues up the flag pole.

      I hope to start in a week or two and I plan to post photos of my progress along with inquiries.

      Floor insulation will be 2x2" Foamglas with 2" calsil on top, total 6". If I could have obtained 3" calsil I would have gone with 7". I found that it is easier to find calsil if you use the brand names. Some sales people connect better that way. I think home oven builders get different sales people than commercial and industrial customers. It was quite an adventure to locate sources for calsil and foamglas in Mexico.

      Herringbone oven floor extending beneath the dome. This just seems easier with less precise cuts needed. Also, (probably of little consequence) there is more bearing surface to transfer the dome weight onto the calsil. I don't think I will wear out the floor bricks in my lifetime and, if necessary, I could veneer with the porous basalt stone slabs available here.

      The vent arch and landing are completely isolated from the oven dome. There is a 2" insulated separation. This gap will have an insulated stainless channel on the landing. I am undecided what insulation material to use on the arch gap - foamglas, calsil, or perlcrete, perhaps with refractory cement or perlcrete veneer. I'll make a decision when I get these materials in hand and with serious consideration of input from this forum. I've never worked with these materials. The concern is spalling down onto the landing and keeping the insulation in place. This area will be serviceable; so I think there is little risk in the experiment. The most complicated solution might be to fit a stainless channel over the entire insulation perimeter.

      There has been a fair amount of forum discussion regarding a thermal break. My thoughts are based on my experience with industrial furnace design. The relatively wide break will lower the heat loss and also mitigate high temperature gradient and thermal strain. A narrower gap would allow for movement, but do less for the temperature gradient. The 2" width can be compared to the 6" or 8" dome insulation thickness. In my oven 2" it fits well into the design with the 6" chimney and excess 2" thick insulation materials.

      The vent arch is only 6.5" long. I am keeping it short for oven access, while the landing extends out, 11" total, (9"brick, plus the 2" thermal break area). Since I have no wfo baking experience, I wonder what others might think of this.
      The chimney will be custom made 6" square double-wall, insulated with perlite. It bears on the vent arch and cantilevers onto the oven arch with insulation islating it from the oven arch. I plan to use high temperature caulk to seal at the brick services and lateral bracing above the oven.

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      • #18
        I started construction I picked up foamglas and enough brick to start the floor, with the remainder of brick to be shipped in. I plan to document here to get input or help others.

        I found that using aluminum angle, which I had on-hand, to be a good tool for inscribing circles. It was easy to drill a hole for a carbide tipped scribe, which cut handily into the foamgass. A box knife cuts the foamglas easily, even after it dulls after the first cut. The 2" foamglas thickness is nice to work with.

        Has anyone used silicone adhesive with foamgas? I was considering sticking the foamglas pieces to one another and the base layer to the slab with RTV silicone, mostly so they don' move during construction. I was considering using silicone to stick decorative tile to the foamglas under the landing, also. The foamglas and calsil will be 48" diameter, protruding about 1.75" beyond the oven base. This is just to utilize the material. First two layers of ceramic fiber will rest on the calsil.

        My dome will set on the oven floor. After seeing the variation in thickness of the floor brick, lippage maybe 1/16", less than 3/32" by eyeball, I was considering using a very thin layer of refractory mortar here to level it out under the dome. It is often recommended on this forum that the dome floats, but I do not see why it would be a problem to use mortar here. So I am wondering if anyone has specific experience here and would care to comment. I will put down porous basalt stone on the oven floor to take care of brick height variation.

        Rob






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        • #19
          Turns out that the refractory mortar I purchased is intended for very narrow joints. After more searching and reading on the forum I see confirmation and discussion of the refractory mortars and homebrew. So, I am considering whipping up some home brew, which might be interesting because local sand here is not silica sand and varies widely. It seems the finer sands used for top coat stucco would be appropriate for home brew.

          I was considering whether sand, brick swarf, or fireclay could be added to refractory mortar to allow wider gaps and filler application. Has anyone tried this?

          Any advice would be greatly appreciated.

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          • #20
            If you add sand to the mortar you will be weakening it by reducing the cement proportion, so not a good idea. Any sand should be ok for mortar , but coarse grains can make application difficult. You can simply sieve out the coarse material. I think the reason refractory mortars recommend it to be only used for thin joints is because it doesn’t contain burnout fibres. You could try adding these yourself. They must be well mixed in for good dispersal which takes around double the mixing time that you’d normally use.
            Kindled with zeal and fired with passion.

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