I don't recall the exact proportions my first attempt at building a smelting furnace from a 30 Lbs refrigerant tank I mixed Gypsum, perlite, plaster of Paris, Vermiculite. The  gypsum (calcium sulfate dihydrate) did not hold up well at all. 2nd try I omitted the gypsum added a small amount of Portland cement, this portion has held up much better, to minimize the spalding in the lower Gypsum section I have applied Sodium Silicate gave it a lite firing and coated the interior with Rutlands fire place patch. this furnace is fired with a simple  propane burner. 1-1/4" pipe and a 1/4" copper tube with a 1/32 hole drilled in the side aimed straight down the pipe. I have milted down Aluminum, brass and copper with ease.

Have you looked at the date of the last post before yours? There are commercial refractories that are not only much more effective and safe but are really inexpensive, especially when you consider how much longer they last.

You might want to read some of Burners 101 sub forum too. Were you to build a 1 1/4" linear type propane burner like Ron Reil's it'd melt your liner and if you'd built a jet ejector type like a: Mikey, Side arm or T it would've melted your liner in about 2/3 the time. 

I'm not making light of your melter I'm just pointing out there are inexpensive alternatives that are several times more effective and much safer. It's obvious you are a good craftsman I really like the looks of your melter.

Frosty The Lucky.

BTW you do realize that gypsum and plaster of paris are essentially the same stuff after the PoP has been mixed and set?

Hi. Not sure if anyone is out there still watching this conversation started in ‘07 or so, but I found it, so maybe…

I’m coming at the issues from a slightly different angle: I want to build a Kuznetsov Russian (masonry) stove. (Check stove.ru if interested and click the little Aa button to translate to English) It will be a high-temp wood burning heater.  I believe temps in the firebox could exceed 2500 degrees F. The intent is for a hot fire to heat up a mass of masonry that then radiates to heat a space over the course of many hours. These stoves are typically built as an inner layer of firebrick, a narrow expansion break, and an outer layer of normal building brick or stone or other high-mass material. So the firebrick is not intended so much for insulation as for just a tough inner shell that can take the harsh conditions of wood combustion. Actual full Chamotte bricks are like 6 bucks apiece, plus shipping, and I may need a couple hundred of them, so I am looking for an alternative for my first attempt at building one of these. Also, there’s a likelihood that some stray building or insurance inspector will come sniffing around and tell me to dismantle it, so I don’t want to spend that kind of money on an experiment and am planning to make my own bricks. I dug up some clay from the backyard, but I’m not quite sure what to mix in. I have perlite, wood ash, sand, and mineral wool or rock wool. Kind of leaning away from perlite, as I feel a dense not-really-insulative brick is what I am after. Not too many here talking about wood ash, but seems to me like a good additive - it’s already burned, what can happen to it? I sifted it through a window screen, so it’s pretty clean, but still has some tiny charcoal bits in it, which may not be bad, since they will burn inside the brick and create tiny air pockets to give a some slight insulative quality. I’d be interested to read anyone’s thoughts on any part of this idea  Thanks!

 

Hi, I accidentally saw this conversation

short answer: chamotte or grog is fired clay. E.g. there is no more moisture in it and no more/ minimal shrinkage or expansion when heated. To achieve these properties you need to fire your clay. In a kiln or hole in the ground or whatever. This will give you the raw materials at the cost of fuel to generate the necessary heat. You could skip that by getting raw grog, crushed toilet bowls or sinks. Still you will need a binder to form a brick from inert grog and then fire it and still need fuel.. Maybe there is a way to use a hole in the ground or an inexpensive throw away kiln to get you started to make your own? 

above are just my thoughts, hope you come up with something cheap and let me know.  This is a good discussion

Have you checked around to see if anyone will be decommissioning a large old kiln for their hundreds of firebricks?  Or rebuilding an industrial furnace.   Not knowing which of the 100+ countries that participate on IFI makes it hard to have someone say; "the guy down the street is tearing down an XYZ and dumping the fire bricks!"

 

Thank you for taking an interest, Monkey and Thomas! I have not checked around, and I don’t have the first idea how to check something like that…I guess I could look up refractories or something…. I am in Wisconsin, so if YOU have some idea where to look in the Midwest, please let me know.
 

 Monkey, yes, I’m kind of thinking I could use some regular brick to make a temporary kiln to make permanent firebrick- I have a lot of salvage bricks, which I did use to make an oven for a charcoal retort (for the garden), but the bricks did not hold up well at all. I have since come across other ideas to smear an insulting layer of mud inside the brick structure (even for a permanent masonry heater), but have yet to attempt…this might be a good place for perlite additive to keep extreme heat from the regular clay brick. 
 

thanks again guys! (I mean that in a non-gender specific way!

Edited December 11, 20214 yr by Mod30
Excessive quoting

56 minutes ago, Greenfire said:

I am in Wisconsin

We won't remember this once leaving this post, hence the suggestion to edit your profile to show it.

IMHO, The easiest grog is made from ceramic chimney liner or tile, available for free at the broken pile of any good mason supply. While there buy some washed sharp sand and some fireclay. Use equal amounts to make a decent cheap refractory.

As to the Russian fireplace, been studying them for years first I have heard of this super hotness.

I know for a fact it is not needed.

 

Call the local concrete company, if they don't carry fire clay they surely know who does. They'll also carry various types of aggregate, sand and evacuated silica spherules (bubbles) for light weight and decent insulation.

For all the time and effort you're investing in making your own refractory liner you could mow lawns or clean stalls and buy a proven refractory for less investment. 

Frosty The Lucky

There is actually high-temp mortar for use in fireplaces that can withstand very high temperatures. Theoretically, the perlight is there so after the initial burn in, it burn off leaving small air pockets that compensate for expansion. Mortar already has sand in it so you wouldn't have to add any more if at all. I would guess 1 part pearlite/6 part high temp mortar/1 part sand. If high temp mortar isn't available (you can order from home Depot or usually get from a tractor/farm supply), I would use white thinset (like you use for laying floor tile or floor/wall tile in showers) way before I used cement. It has a lot better resistance to moisture, whereas cement just drinks it up, which probably contributes to it's cracking when mixed with clay and sand. The glassy soft wall the one gentleman mentioned is likely from adding too much pearlite and sand, which when heated in a kiln or blast furnace turns to a glass/ melted plastic like substance. Like I said, easy on the pearlite.

Welcome aboard Absalom, glad to have you. If you put your general location in the header you'll have a much better chance of meeting up with members living within visiting distance.

I hate to pop your bubble but fireplace mortar can NOT withstand "very high" temperatures, no fire place bricks reach high orange heat. Mortars are for cementing brick or other masonry together and has a very short life expectance when used as a flame face.

Propane flames are VERY chemically active and mortars are formulated to be sticky, NOT flame resistant. At working temps propane literally causes refractory mortars to crumble. Vermiculite is basically puffed mica and breaks down dramatically before it reaches 2,000f. Some folks use Perlite as a secondary insulation outside a hard refractory inner liner (flame face.)

Even using one of the water setting, 3,000f high alumina refractories like Kastolite 30 so often recommended here we recommend a final layer of kiln wash to improve the liner's effectiveness and lifespan.

And NO, this is not "theoretical" this is empirical data generated by the experiences of people who use propane forges.

Frosty The Lucky.