Castable Refractory Cement to Stainless Steel Fibers ratio

Does anyone know the ratio of stainless steel fibers to cement? In the instructions it calls for one bag of fibers to 3 bags of refractory cement but it does not specify the size/weight of either bag. Also the materials list doesn’t list the fibers. I’m researching the 40" Mattone Cupola

Hi Frank,

The mix is 1 pound stainless steel fiber to 50 pounds castable refractory. The fibers are supplied in a one pound bag, so it’s basically one bag to one bag.

Here is the full guide on mixing. You’ll find the ratio listed there.

[As I read your question it sounds like these may be contradictory instructions, so there may be further guidance coming along!]

When you look at that FAQ, the photo shows the refractory being held by a bare hand. Brickwood has said in the past that the photo is for illustrative purposes, and refractory should be handled with gloved hands only (whether or not the stainless steel fibers have been added—they would only make it worse!).

Hope this helps!

The instructions for the 36" Cupola says add one bag of SS fibers to the mix. should it be three since it instructs to use 3 bags of refractory per cement-mixer full???

No matter the mixing method, the fiber to castable ratio is:

The problem with mixing Castable Refractory in a cement mixer is the refractory starts to adhere to the mixing paddles… so we recommend mixing no more than 2 bags of castable refractory (in a mixing bucket / pail) at one time.

Additionally, it’s considerably easier to gauge / judge the amount of water you add to the refractory as you mix the refractory w/ COLD water. And refractory needs VERY LITTLE water… just enough to pass the Ball in Hand method.

Here’s a great article about mixing Castable Refractory w/ Fibers & water…

Thank you!
BTW the instructions on the website for the Mattone Cupolua 36" say to BOTH use a cement mixer to mix THREE bags and sure seems to say 1 bag of SS fibers per 3 bags of castable. Very different from this article that stresses no cement mixer, only mix in a wheelbarrow or tub, and only TWO bags at a time.
One bag of SS fibers to one bag of castable, got it!

Hear ya on that. I know that @BrickWood is working on revised instructions for all the ovens, based on the huge “knowledge base” of experience that comes from these message boards over the past few years.

When in doubt, I’d always recommend asking (as you did here, and thank you!). There were a couple of points on my Mattone Barile Grande build that were unclear, but lots of experienced help to point me in the right direction.

As a final pointer, if you’re in a very warm climate, substituting ice for water can help. You need to be careful not to make the end product too runny, but it’s an effective way to absorb the heat that comes from friction while mixing.

Keep us posted on your progress!

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