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Searching for WFO building material in Japan

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  • Searching for WFO building material in Japan

    Sorry to be posting so much here but I wanted to just throw it out there to see if the fornobravo experts can give any inputs/opinions.

    I'm trying to find the building material for the dome work. As far as I could read on here, there are basically two options: (i) to find dedicated fire mortar; or (ii) to make a home brew consisting of 3 quarts sand 1 quart each of lime fire clay and portland cement.

    The portland is easy to find, as is the sand. But for lime, all I can find is lime for gardening/agriculture. See attached image.

    Washed clay also isn't easy to find. I found some (attached image), but our garden is full of clay, so collecting and washing that is also an option I am considering.

    If I go with a dedicated mortar, there seems to be two options, although they may be very different. One of them is called 13T Castor (see attached image). It seems to be a refractory cement used for kilns and ovens. But as far as I can gather, this is a refractory cement used in stead of firebricks, and not to create a bond between firebricks. In that sense, it might be the right thing to use on top of the firebrick dome, to strengthen it. It seems to have a ceramic mix/fibres that make it strong and able to withstand high temps. So maybe that is NOT what I am looking for as bond between the firebricks.

    The other option is called SK 32 (see image), like many firebricks here also are called SK 32. This seems to be a fire mortar that can withstand high heat. The problem with this mortar, at least according to google translate, is that it can be used over and over again. If it's dry you just add water and it becomes malleable again. So basically if I used that to bond my firebricks, wouldn't they fall apart if they get wet?

    It is pretty difficult to find the right materials here, especially when challenged by language gaps.

    I wanted to throw these issues out here to see if anyone knows what it is I should choose as bond between my firebricks.

    Cheers from sunny weather in Japan.



    My build:

  • #2
    Update on the building material in Japan just in case it can come in handy for others in similar situation.

    I bought 25kg of refractory cement mix (previous post the 13T Asahi caster bag with blue lines) for around 40USD, pretty pricey. I then realised that this cement apparently doesn't 'stick' but is used as refractory 'filler' between large joints or even to cast refractory bricks. So probably I should not tell my wife that I may have made a mistake in purchasing this.Or can I use it in place of portland in a homebrew mix?

    Meanwhile, since Japan is really famous and has an age old tradition for pottery and porcelain, I found a large variety of clay types for sale online. Prices vary, but simple clay seems cheap for 10-15 USD per 25kg bag.

    I also found what they call 'tool soil' or 'Dosen'. I believe this is google translate mistake and that this may really be fire clay. See the attached photos, it seems this has a good 25% aluminium and 65% silica content - DavidS that's fireclay right?

    They also sell 'chamotte'. I believe this is fired clay that doesn't shrink and can be used in stead of sand to make a home brew, but I'm not totally sure.

    I'm still empty handed on the slated lime but will keep looking.

    There are also various types of refractory mortar. I believe contrary to the refractory cement mix which I already bought, that the mortar acts as a glue between the bricks. It should only be used for relatively tight joints so probably would not be the best 'filler' material for the backside of the dome. The problem with the refractory or fire mortar I've been able to find around here is that it doesn't harden until fired at high temperatures, and if it gets wet, it falls apart. Is this unique for the fire mortar sold in Japan, or is this simply a characteristics of fire mortar in general that I seem to have missed? Should I go ahead and get such a fire mortar and just keep the dome covered until it's really finished and stucco'ed?

    It's a fun project that raises lots of questions and a good excuse to increase our common pool of knowledge about these kinds of things.

    My build:


    • #3
      I can’t read the writing on those pics, so it is difficult to see what they are. Some clarification on terminology may help.
      Refractory cement is pure calcium aluminate cement, with no other additives. Ordinary cement is calcium silicate.
      Refractory generally means “fireproof”
      Refractory mortar is a mix containing calcium aluminate cement and a fine aggregate.
      Castable refractory is a mix containing calcium aluminate cement, fine aggregate and coarse (around 4 mm aggregate).
      High temperature aggregates (good for around 1450C) are not required for an oven (Max 600 C) normal sand will suffice.
      Fire clay in the building industry refers to any cheap powdered clay used to make a mortar more workable.
      Fire clay in the ceramics industry refers to a clay that will withstand porcelain temperatures (1300 C+) where a high alumina clay is called for, ie one with a high alumina and low silica content.
      As our ovens work at much lower temperatures any powdered clay will suffice because there’s insufficient temperature for the silica to turn to glass.
      The lime in the homebrew must be hydrated or hydraulic lime. Agricultural lime is unsuitable. Look for builders or mason’s lime.
      Chamotte is fired and crushed clay, again not required for the temps we use. You could use it but you’d be wasting your money. Bricklayers sand will suffice.
      Kindled with zeal and fired with passion.


      • #4
        Thank you for the detailed info. I guess I can use refractory cement then as well as refractory mortar for brick joints, is that correct?

        And btw could you tell me please - how come some types of refractory mortar do not harden until around 800 C and are not water resistant until that point? I guess I need to steer clear of those kinds of mortar and find something that cures on its own at normal temps.

        Yes, all the kanji is really confusing for me to understand the small differences between all these products. If I can find hydrated lime/mason's lime then I will go the way of homebrew, just to avoid picking the wrong 'refractory' ready mixes that are available.
        Last edited by Yokosuka dweller; 12-10-2019, 06:05 AM.
        My build:


        • #5
          I am pretty sure you need air set refractory mortar not heat set that you are describing.
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          • #6
            Mortars relying on temperature for hardening use the process of sintering which occurs north of 573 C. This is where the clay becomes irreversibly permanent and will not return to mud in the presence of water. Other mortars rely on cementious materials like Portland cement, calcium aluminate cement or hydrated lime which use a process called hydration to set chemically. The 3:1:1:1 homebrew has proved to be most suitable, economic and workable for the temperature range of our ovens and in most cases outperforms higher temperature rated commercial products.
            Kindled with zeal and fired with passion.