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high temp refractory cement

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Will a thick wall of high temp refractory cement (5000f) work on its own to line a propane forge? What is the benefit to lining with kaowool?

I'm planning my first shop made propane forge, I can't find kaowool locally, but can get other ceramic high temp insulation. However I have come across reasonably priced high temp refractory cement (5000f), I'm thinking this will work like fire brick. The benefit being that I should be able to patch it with left over cement later when the flux has damaged the inner surface. Any thoughts, advice, warnings?

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The problem of using something solid like refractory cement(after it sets up) or hard fireplace fire brick is that it has only minimal insulating value. It will work but will cost you in terms of heat lost.

Look on the net or ebay for ceramic insulation blanket. It isn't terribly expensive and is really a lot better in the long run for a forge.

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With a thick layer of the cement can I get by with lower rated insulation ( 2000f) or (2300f) between the cement and the outer shell? Or is a higher rated insulation and thinner layer the better way?


I would get a higher rated insulation, but yes, the refractory cement will protect the the insulation for the most part. I built 2 forges with ceramic insulating blanket covered by a somewhat thin layer of refractory mortar (cement;mortar/ potato;patahto) The stuff I used, AP Green's Greenpatch 421, is rated for 3200ºf and I put it over the wool which I believe is rated fro 2600º or 2700º in 2 layers totaling maybe a 1/4". One for is a naturally aspirated 1" burner freon tank forge and the other, a 1.25" forced air in a 15" x 10" dia tube type. both will weld and the blown forge will even burn steel. They get plenty hot and the insulation seems to be holding up fine after several years use.

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I have many students through the shop and they are rough on the fiber wool lining. Flux will also eat through the wool.


In general for light forgings and on/off use the wool is very good. For longer burns and full day use the refractory is good.

The greater mass takes longer to heat up, but that thermal mass will allow you place large amounts of metal in there and get less temp drop than wool alone.


For long days of forging I have a preheat chamber for the stock to be fed into the forge so the exhaust gas warms the next bars to place into the forge.


Industry has blocks of the fiber wool in pre-made bundles and they are bolted in place to line the furnaces. Others spray the refractory cement into place much like gunning in cement for construction jobs.


I rather like Mizzou plus castable, but I have several thousand pounds of the stuff. I also like the Bio safe wool that has come on the market of late. Superwool® HT is one brand.



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The best thing to do is use a combination of materials that maximizes their strengths and minimizes there weakness.


2" of a batt insulation like Superwool or Kaowool will keep the heat in the forge chamber, but it's easily damaged.  So apply a quarter-inch of refractory cement over top of it.  You get a hard surface, armor-plating the soft batt, while retaining the better insulating quality of the batt.


My Majestic forge uses solid insulation, including hard bricks for the floor.  It's the biggest gas hog I could imagine, and it radiates heat far more than it should.  The softer cast insulation on the sides and top of the chamber is extremely soft, easily chipped and abraded by the stock being heated or the tongs reaching for said stock.

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I use 1" of Inswool, 1/2" of Kast-0-Lite and then paint over the casting with either Plistix or Metrikote.  I do the floor in the same manner.  The Kast-0-Lite is resistant to flux.  After forging all day long I can reach up and touch my forge shell without getting burned.  The Inswool, Kast-0-Lite and Infrared Reflective top coat are keeping the heat inside the forge where it belongs.


When I built a forge for a student from a 20# Freon bottle after the casting had cured I put in a piece of 1" square and timed it to forging temp.  It took 11 minutes.

The next day I painted the interior with Plistix, then put the same piece of 1" square and again timed it to forging temp.  This time it took 6 minutes.

I think that this means that if you use an Infrared Reflective product you are going to use half as much gas,

get twice as much work done,

at the end of the day be twice as tired, and

go in the house and drink twice as much beer.


Let me know if I can help you.

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  • 4 years later...

quick question,  I am getting ready to build a gas forge from an old propane tank.  After reading a lot of posts, my thought are to line with minimum of 1" kaowool or equivalent (outer layer) then about 1/4" ITC 100 or equivalent for the inner layer.  Fire brick on the bottom for the flat surface (on top of blanket liner) and also coat with refractory.  Good idea, bad idea, better ideas?

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