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Homebrew AR Fiber Dispersal (What works best)

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  • Homebrew AR Fiber Dispersal (What works best)

    I will be building a 32” oven using the latest homebrew castable ratio of 3:1:1:.5. To this mix I will incorporate AR fibers for strength/shrinkage control (4% by weight) and burnout fibers for spalling prevention (handful per 2-3 gallons). I will not be using SS needles.

    I have combed through the build threads, sourced the products needed and am in process of acquiring them. The biggest issue that I continue to see has to do with proper distribution of those pesky AR fibers, I’m trying to work out a plan to manage this. I’m assuming whatever works for the AR fibers will work for the burnout fibers.

    I have noted that breaking up the fibers by hand as much as possible is the first step, but what about after that?

    Mix the dry ingredients using a drill/paddle attachment to ensure that the fibers are well dispersed and storing in 5 gal containers until needed.
    Create a slurry and mix in the fibers at that stage.
    Mix in fibers at the very last stage once the right mix consistency is reached.

    To assist with the mixing I have a low-speed high-torque drill with paddle attachment that I’ve used for other cement projects. Or I have a wheelbarrow and hoe.

    What is your experience? Since most builds here are folks who built their first homebrew oven by following advice buried in these pages and winging it, what would you do differently after what you learned during your build process?

    Myself and future builders will appreciate any insights. Thx.

  • #2
    Firstly, I think you’ve gone too heavy with the AR glass fibre addition. 2% by weight is a better ratio. My experience with AR fibres , from two different manufacturers , is that they both disperse readily. Both were 19mm in length and quite visible in the mix, so it’s easy to see how they are distributing.
    The very fine pp fibres by contrast, do not disperse readily and I find mixing ( by hand in a barrow with a spade) is the best way, so you can inspect the dispersal as you mix water to the dry ingredients progressively. Attempting to disperse them into the materials prior to mixing with water seems like a good idea. I tried this and discovered that it actually made matters worse, with the fibres clumping together like a fur ball. Far better to add them into the wet mix, pulling them apart as much as possible then extend the mixing for double the time you would normally use. Because they’re so fine they are really difficult to see in the mix.
    I also use basalt fibres for reinforcement, but the ones I have are a range of thickness and length. I find they clump worse than the pp fibres so always prefer to use the AR glass fibres.
    Kindled with zeal and fired with passion.


    • #3
      Thanks as always David. I really had this somewhat backwards as I thought the AR's were more difficult to disperse. Oops. Do you think a stiff slurry, wet enough to agitate with the drill/paddle and then adding the fibers would work? Working in the remaining dry ingredients by hand once the fibers are dispersed well into the slurry?

      Just looking for the easiest way (excuse my laziness), appreciate your help!

      also, I’ll back off on the qty of fibers needed to 2% by weight.
      Last edited by WaterDog; 03-24-2024, 12:39 PM.


      • #4
        Just a quick follow-up. As usual, David had it right and my concern was a bit unfounded. Mixed up my first batch of homebrew with 2% AR fiber and a handful of poly burnout fibers. Using a hoe I added the fibers while adding in the water. I broke apart the poly fibers as I added them while sprinkling the AR fibers over the surface bit by bit. Mixed up well but I probably worked the mix twice as much as I normally would.

        In the end I ended up with 'hairy cement'. If you look at the picture you can clearly see the tiny poly fibers and the thicker straight AR fibers.


        • #5
          Hey waterdog. Love your castable. I'm ready to cast. The vermiculite layer and bricks are done and I have a mold and all the raw materials -- except for the fibers.

          I'm in the US. Where did you get your fibers. I know you can't post links here, but if you can give me product or distributor names I would really appreciate it.



          • #6
            totalnewbie I got the fibers from Glob Marble, Coney Island, NY. I had a really hard time finding fibers locally (CT) and I initially found these on Azon. Since they weren't too far from me I made the trek to their store. Commercial supplier. They breakdown large bags into 1 lb units for selling to folks like us. They're manufactured by Nippon Glass of Japan. They look like the real deal as compared to a cheaper bag I bought from Azon that looked more like poly fibers than what these are. Happy with the purchase. Look them up and give them a call. They told me they'll ship via priority mail flat rate box.

            BTW, I used 5 lbs for my 32" dome and gallery. Cleaned out the sand today and letting everything cure covered for a week..

            Good luck with your build!


            • #7
              Did you get AR fiberglass from Glob Marble? Or the poly burnout fibers?

              This is all very confusing. :-)


              • #8
                AR fiber from Glob. While they do sell them by the lb on Azon their shipping cost for multiples is too high IMO so I went direct. They have a website, call them.

                Poly fibers I bought on Azon. Have a bunch left over. DM me if you want them.
                Last edited by WaterDog; 05-18-2024, 02:58 AM.


                • #9
                  I ended up getting both the AR fiberglass and poly fibers from Amazon. The poly ones are very fine, so I think they're the right thing. I mixed the homebrew -- I went 5:1:1:0.5 -- with water until is was ready to go, and then hand and trowel mixed in the fibers to disperse them, around 1% each. Yay. Now I get to wait and see what comes.

                  WaterDog, how long did you wait for the mix to dry before you removed the mold?

                  And then how long are you going to wait before your first curing fires?

                  I'm planning on curing the oven without the outer insulation in place because I want to see how big the cracks are! :-) Does that seem like a good idea?


                  • #10
                    [QUOTE=totalnewbie;n458806]I ended up getting both the AR fiberglass and poly fibers from Amazon. The poly ones are very fine, so I think they're the right thing. I mixed the homebrew -- I went 5:1:1:0.5 -- with water until is was ready to go, and then hand and trowel mixed in the fibers to disperse them, around 1% each. Yay. Now I get to wait and see what comes.

                    I think your 5:1:1:0.5 mix could be a bit weak although it will probably work ok. The tried and true 3:1:1:1 has been the standard for a very long time. Read my discussion on this point on my recent post here

                    Kindled with zeal and fired with passion.


                    • #11
                      totalnewbie broke down the sand mold a day and a half after the cast. Luckily no major voids to contend with. Letting it dry out for a couple of weeks before I add the insulation layers.

                      Perhaps it’s too late but it’s not advisable to begin curing fires without insulation as it will promote cracking because of the localized thermal expansion that will occur and the ability of heat to readily escape to the outside. I’m taking my time.
                      Last edited by WaterDog; 05-24-2024, 09:42 AM.