Metal Casting Zone

Hi there, yesterday I 'lined' my new furnace, but due to looking after a little boy at the same time, I wasn't concentrating, and discovered this morning that I have a large number of medium sized voids in the refractory on the inside face. Can I simply make a new small batch of refractory and fill the voids, or should I rip it all out and start again? I have enough left-over ingredients for either.

Thanks, Frazer.

If you haven't fired it yet, shouldn't be a problem. Is it clay or commercial refractory? If it is commercial refractory it may eventually fall out, but it's worth a try to patch it. Mix it a hair wetter than you regularly would and work it in to the surface good so you will get good adhesion. If it's clay, and it isn't fired yet, absolutely no problem, slightly moisten the surface and trowel it on. Let it dry and fire it up.

It's sand, vermiculite, portland cement and bentonite. I feel it should work, and I haven't fired it yet.

Thanks OddDuck

Please tell me you aren't going up much past aluminum temps, or that you are going to be using strictly charcoal. Be careful with the heat, the mix that you have is full of fluxes, and while it looks like it works great for a while, it's gonna crumble on you. Don't get me wrong, except for the bentonite, I used a very similar mix for my first furnace, it does work. You are going to be spending a lot of time patching. The portland will break down eventually, and it will fall apart. Mine lasted for about a year or so, but I was constantly patching it. If you can find a supplier locally, get some fireclay or commercial refractory when you go to build your next one.

Brass will be the absolute hottest with this one, I should think, and I'll only be using charcoal, as I can make it for 'free'.
What did you use instead of bentonite? I haven't found a supplier of either fireclay or commercial refractory, and I think that it will be incredibly difficult to do so here in Canberra, you can't buy much here.

What would you suggest as the ideal refractory mix? Bearing in mind the aforementioned difficulty in acquiring fireclay.

canberra???? you should be able to get fireclay! from a hardware store! bunnings sell it ! is there a bunnings near you??



www.foseco.com.au have their main office in sydney. $65 au for a 25 kg bag of 2000 deg refractory. i would go with fireclay! its cheaper. my furnace lining cost me $5 (half a bag of fireclay.)

I'll check again, but none of the hardware stores admitted to selling it. Are you in Canberra xl? I'm out of town for a while, but when I get back I'll have another look. Thanks.

Okay, it should hold up fairly well with charcoal. If you were using propane or waste oil you would eventually have problems. As far as an ideal mix, you will get five different answers if you ask five different casters. If you aren't going to use commercial refractory, the state of the backyard art is probably clay/foam with as thin a hotface as you can manage. For my furnace, I found a pottery supplier and got EPK kaolin, which is a very high purity clay that fires at a pretty high temp. Mix this with calcined alumina in the correct ratio and you get mullite after it has been correctly fired. Mullite is very refractory, and will withstand a lot of thermal cycling.
I'm definately of the "whatever works" and "I already had it so I used it" school of thought, and the point is playing with fire and pouring metal. Be safe, and have fun!

bowlerhatman wrote:
I'll check again, but none of the hardware stores admitted to selling it. Are you in Canberra xl? I'm out of town for a while, but when I get back I'll have another look. Thanks.no i live in brisbane qld. when i asked around i was told "no" dont sell it! bricklayers clay???? yes sure do!!! see the side of the bag (fireclay!)

Right, I'll try that next time. Thanks xl