Hi Zachary,
All I can add at this point is to repeat much of what Al has just shared...
We are running into a lot of questions about RMH and other topics from folks that, I am sorry to say, watch way too much Youtube.
Yes there is good info out there, both on Youtube and in the general body of the internet....however....only about 20% (more like 5% from what I have been told by those that actually study the overwhelming mass of it) is of any use or coming from reputable sources with more than 15 years of
experience in a given subject (15 years being a baseline for knowing the "ins and outs" of a subject to then teach others about it...)
Again the video that Amos has shared is another "DIY Refractory" of unknown thermal characteristics or durability. Some of these formula modalities have inherent good thermal insulative characteristics...but...that does not make them actual "castable refractories," and I don't want us to get into the habit of repeating bad information and/or partial information unless we know for certain that the information shared is worth passing on, either from our own experience or years of working in that particular discipline/field of study.
To be an actual
"castable refractory" The material will not contain any regular OPC (ordinary portland cement). For high-temperature applications you find in kilns, crucibles (probably the most enduring of this lot,) ovens, stoves and the related combustion chambers, will require the use of a refractory matrix. OPC base matrix will be damaged or destroyed by elevated temperatures, and any formula using them are doomed to eventually fail if not sooner...not too later. Base fundamental materials that always are in, as far as I have ever learned or experienced, castable refractories will have their base components made of major portions of calcium aluminate, fire clays, ganister and minerals high in aluminum content.
There are even really good articles here at Permies on this subject.
Playing with castable refractory is an excellent example.
Most folks are trying to "cut corners" on cost of many refractories...they can be very expensive. Unfortunately, that is just the nature of the materials in them and the cost of time in using materials that are not meant to be used this way...is not only costly in and of itself...it can be dangerous. I would also note here that even among refractories, many are consider a "sacrificial element" and are often designed (or should be if the design is a good one) to be replaced and/or service when needed.
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