This is a formula for making excellent refractory material to use to line the walls of a melting furnace. I am routinely melting aluminum and brass and I have been looking for a formula that is strong and lasts a long time. All of the formulas that I have seen that use Portland cement need replacing pretty often because Portland does not hold up under heat. Anyhow, I have finally found a formula that works pretty well. It's hard as rock and has good insulating qualities. You can make bricks or whole furnace linings with it. And.... You do not have to worry about a steam explosion if you don't cure it correctly. I have made shapes from this material and fired them while wet with no problems. If that were not enough: It's cheap! I am very excited about this and I want to share it.
- Kaowool, also called rock wool.
- Refractory clay. I use green stripe, but any refractory clay would probably work. Note that this is not just any clay. Refractory clay has a different chemistry than pottery clay.
- Perlite. This is a mineral material that is in gardening. If have looked into DIY refractories, you have probably head of it.
- Optionally, Sodium Silicate. Also called water glass.
- Breathing protection. Seriously. The materials that are used are nasty. There is no way you can try this without some kind of breathing protection. Silicosis is a nasty, nasty disease that cannot be cured. Use breathing protection when handling these materials.
- Face/eye protection. You do not want to get this stuff in your eyes. This is nasty stuff.
- Some kind of power stirrer. I used one connected to my drill. You will need it because stirring this junk by hand is not an option.
- Buckets and something that you would use to mix concrete in.
- Measuring cups. I got mine at Home Depot in the paint department. Buy extras. They really are handy. One measures up to 24oz and the other measures up to 64oz.
- Some kind of scale that can measure grams. I bought mine on Amazon for less than $10. It only needs to go up to a kilogram or so.
Get it done:
This formula makes about 5 gallons of refractory. If you need more or less, just keep the proportions the same. It seems like the proportions do not need to be exact. Just get it close and you should be OK. If you experiment with it, I would be very interested in hearing about your results. That's the fun part AFAICT.
You need the following:
- 300 grams of kaowool. That is not very much. A 12"x12" sheet will probably do it, plus some.
- 64oz (by volume) of refractory clay.
- 96oz (by volume) of water. Note that if you want a very hard surface, you can use 1/2 the volume of Sodium Silicate 40%. I find that it's not really required, but if you are casting the bottom of a furnace that will be used pretty hard, maybe it's worth the extra expense.
- 400oz (by volume) of perlite. That's a little less than 5 gallons. (did I mention breathing protection? Use it.)
- 48oz (by volume) 40% Sodium Silicate. S.S. acts as a binder and hardens the mixture.
How to do it:
- Weigh the kaowool and break it up into a bucket. It strips off in thin sheets. If you tear those up a little, it makes mixing easier. Not really required, but recommended. (breathing protection)
- Measure and add the refractory clay to the bucket. (breathing protection)
- Add the water to the bucket. You can use less. Less is better. I find that 96oz is about right. You can use a little more or a little less, depending on what you want. If you want to use Sodium Silicate, then mix it with the water before hand and add that way.
- The amount of Sodium Silicate is about half the volume of the water. The total amount of liquid will be about 96oz for this batch.
- Mix it. No kidding, beat the heck out of it. Mix it completely and then mix it some more. You have to break up the kaowool. This is absolutely the most important thing there is to a successful batch. The kaowool must be completely broken up with NO clumps. I run my fingers through it to check. Also the clay needs to be completely mixed, but if you mix the wool correctly, that will be done too. It will be about the same consistency as if you had only mixed in the clay with that amount of water.
- Measure out the perlite and add it to the mixing tub. (that stuff is nasty to breathe)
- Add the clay mix to the mixing tub.
- Mix it completely until there is no dry perlite. You should see no trace of the kaowool in the mix. It will completely disappear. If you see any clumps of it, then you need to do something about it. (I don't know what) Your batch of refractory may not turn out as planned.
- After the batch is completely mixed, then it is ready to be pressed into a form. I have only used hand pressure. I do not use any kind of tamper. That seems to work well. If you pack it too close, it may have an adverse effect of the insulating qualities of the material. I don't know as I have not tried it. Cast it into bricks or directly into your foundry furnace.
- Sodium Silicate hardens on exposure to CO2. That means that it will eventually harden in the bucket, though it will take a while. Just don't plan on storing the mixture for a long time.
- You can mix the kaowool in just water. It should be possible to cast it just like the refractory. You would want to strain the water out of it. Maybe add some Sodium Silicate to it. Remember that the wool insulates by trapping air. If you make it solid mass, there will be no insulation. It would stand high heat, though.
- Kaowool with refractory clay and some sand (instead of perlite) should make an excellent crucible. I have not tried it, but I plan to.
- I made a small batch and then made a couple of 3" balls. I fired them straight after forming them without letting them dry -at-all-. They fired just fine. Hard as rock and light as a feather. Impressive.
Where to get this stuff:
- Perlite is available locally at garden centers. Ask if they can order it for you if they don't have any on hand. I got 4 (cubic) yards of it for about $20. That's enough top make about 30 gallons of refractory.
- Refractory clay. I have a pottery dealer locally, and I get a lot of my stuff there. They sell a 50 lb bag of dry clay for $15. Here is a link: http://www.armadilloclay.com/
- Kaowool. It's about $5 per square foot. Also at: http://www.armadilloclay.com/
- Sodium Silicate is available on Amazon or on Ebay. A gallon costs about $20.