Homebrew AR Fiber Dispersal (What works best)

[WaterDog]

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.
Or
Create a slurry and mix in the fibers at that stage.
Or
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.

[david s]

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.

[WaterDog]

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.