thomas rubino wrote:Josh ; I have built both. The cast core will burn hotter and faster than the brick core. But... the cast core is fragile. If your rmh is in an insulated home(mine is in the greenhouse) with careful adults adding wood then a cast core is a good choice. However you can totally destroy the feed tube side as well as the roof of the burn tunnel if you treat it like a regular wood stove. I've included a couple of pictures that show how my feed tube went from 7.5x7.5 to the size of a 5 gal pail, over the course of a winter, the feed side of the burn tunnel roof also caved in on me. I rebuilt using firebrick. Now it takes longer to come up to temps and until it gets there I can only get apx. 800 degrees on the barrel top ,after a while i can push it over 1000. My cast core regularly ran at 1100 degrees, FAST. Keep calling around on looking for fireclay, I called many/many building supplies and most did not know what fireclay was much less where to get it ! Finally called the right place and wala a whole pallet full at 20.00 a bag , later I found it even closer at 15.00 a bag I also was told in spokane it can be got at 10.00 a bag. The cast riser however is AWESOME !!! Use a 16 gal barrel as the outer form,use sonotube or just thin wall stove pipe for the inner form . Mine is on its second season and its good as new ! I was able to just lift it off when I did my rebuild and just set it back in place when I had the new brick core ready! Good Luck keep us posted and send pictures !
thomas rubino wrote:Josh; One 50# sack of fireclay and apx 2'of perlite should be plenty for a riser. however I would buy at least 2 bags(or more) of fireclay and a 4 cubic foot bag of perlite just to make sure. Also that way you will have a start on materials for your second rmh,lol. Build your core first ,in fact, fab it up(with no mortar) outdoors and try it first. Then build it indoors. After your core is ready then pour your riser next to it on the ground and lift it into place when ready. I've included some pics of mine. The first is brand new, next is at the end of the first season covered in ash and the last is after its mounted on the rebuild. Go to youtube look up (broaudio) this is matt walkers page (a respected rocket builder) watch his videos of cast core and cast core part two.
Sean Fitzgerald wrote: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!
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