I used the rutland to make a rear liner in the back of my furnace. It got thru most of the season but cracked in two places and eroded pretty bad. Not sure if there might be a better choice of refractory cement or if the failure was pilot error.. Here's the thread I documented it on.End of Season Clean Out - Rear Liner Burn Thru Clayton
Lightning - You did one helluva job on your firebrick casting...it looked great!
From what I've read on the web (mostly from those that make their own forges & foundries from castable refractory mixes) I've learned there are a few things that others say can cause poor longevity of homemade Rutland firebrick. They're usually related to water, such as:
1. The mix was "too wet" (use less water - but never more - than Rutland recommends). Better results seem to come from mixing it to a soft clay or putty consistency and pressing it into the mold, rather than something close to a "pourable" or loose consistency. You should be able to make a "snowball" out of it and it should keep it's shape if you toss it an inch or two in the air and catch it in your hand several times. Because I've never mixed any before, I have no idea how wet Rutland's recommended water amount makes the mix. Wetter mixes usually make weaker firebrick that crack easier and wear away faster from abrasion.
2. A rough textured surface should be obvious after screeding the mix level in the form...similar to concrete block. A drier mix should allow this. The surface should not be troweled or made smooth because it hinders the evaporation of moisture from the brick (even when slowly dried with heat). Trapped moisture in the firebrick can cause cracking, spalling & blistering when exposed to the higher temperatures of burning wood or coal. Several small, low heat fires after installation are recommended...even after the firebricks have been slowly dried out in an oven.
3. The addition of stainless steel refractory needles greatly improves cracking and abrasion resistance.
4. Supposedly, properly cured firebrick don't expand when heated in a firebox... or if they do, it's very, very slight. Sometimes cracks are caused by something else (surrounding metal?) that expands against the firebrick and puts pressure on it. In my project I will leave about 1/8" gap around the firebrick edges, at the metal walls of the firebox.
We'll see how this info works out in my project. This is advice others have shared from their experiences, so it's the method I'm going to use.