Hi everyone, I am new to the site... I am working on a solution to heat my uninsulated studio.. We are renters so insulating is not really an option. I just wanted to lend some of my professional experience as a potter.. Also, to you folks living in MT you should call the Archie Bray Foundation its an old brick factory turned ceramic mecca. They do sell fireclay by the ton and should have a never ending supply at a good price. On average, nationwide, a bag of fireclay should cost $12-$15 per 50lb bags. Less if you buy more..
I wanted to give you some info on castable mixtures, I have been building kilns with this stuff since undergraduate school. In areas that are not going to reach (Quartz Inversion approximately 1000 degrees F in ceramic jargon) the fireclay will never make the magical switch to fired clay. So anywhere you put this stuff that will not reach Quartz it will always be susceptible to being crumbly and it will not be waterproof/freeze thaw proof. So if you expect your heat riser to actually reach these temps then you can reduce the amount of cement needed to form it. So when you are building your suitable mixtures you can keep that in mind. This bond is called a thermal bond. In areas where you will not be reaching Quartz you will need to have a hydraulic bond (like the bond you get from plaster and cement) in order to maintain its rigidity.
In the ceramic world we differentiate the bricks mainly by density and thermal properties. Firebrick is a specific term for Hard Brick. Insulated Fire Brick is a specific term for Soft Brick. Soft brick is relatively new... However, it is made with the same materials as Hard Brick. Its duty rating (heat resistance) is based on its purity and frankly I've never understood why they are more expensive. If you want to create Insulated Fire Brick, or Soft Brick, you need to create air voids in the mix. You can achieve this by adding carbon based material, sawdust, spent grains from a brewery, etc. The particulate size will give you variable size holes in your refractory mix. A word of caution here I have made castable with bigger sawdust and the size of the void does make the mix even more fragile. Now this will work if your mix, fireclay (or any clay actually--I can answer any questions on this topic) sand, cement reaches at least 451 F (this is when wood burns, all chemical carbon with burn out at Quartz Inversion). I see that a lot of you are using perlite which is a igneous rock--good choice as a fill material but it does carry with it issues too. One, it has a very low melting point. Two, chemically it releases its H2O with heat and expands which may be another reason I see that you all have a lot of steam/water collection. It does lend itself to being refractory so it is a good choice as a fill. Again, we potters totally geek out on this stuff so I could go on..
If you really want cheap insulation for heat risers and insulation is really what you want/need for a riser personally Id cast a core of a fireclay, sand, sawdust, cement (just enough to make it hard enough to move around before it is "fired" then wrap the whole unit in Kaowool. That stuff is amazing. I can line a galvanized garbage can with 1" and fire it to 2000 F in less than 20 mins with a propane burner and the can doesn't lose it zinc... The fireclay skin will prolong the life of the Kaowool... Just a side story, this is the stuff the "tiles" of the space shuttle were made of... Very fragile.
Thanks for all your info.. I'd love to hear more of some of the room temps you all achieve with your heaters. I hope this info helps you guys!
