Johnny Chesser

Is plaster of Paris mixed with sand a good liner for a forge?

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Hello, and welcome to IFI. If you have not already, please READ THIS FIRST!!!

The short answer to your question is, "Yes, and more." It's a bad idea, don't do it, and if you want more information, read the post I just linked and do what it says there.

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Welcome aboard Johnny, glad to have you. POP and most anything is not a refractory. At best it will erode quickly at worst it can spall and throw bits of HOT plaster around the shop.

Iforge has a LARGE gas forge section with all a person needs to know. Forges 101 is the most current active thread and has info about forges, liners and safety. We're REALLY BIG on safety here. :)

Frosty The Lucky.

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You made Damascus blades from mild steel?  The point is mild steel has a higher forge welding temperature than high carbon steel.

Regardless, if you are able to forge weld high carbon steel with it you are getting pretty darn hot.  However, the fact that the plaster of paris DIY "refractory" is a heat sink compared to commercial refractory and ceramic fiber blanket still remains.  If/when you change your lining or build a new forge with more appropriate materials you will most likely notice a difference in fuel consumption.

Is that 1400 degrees C or F? 

If you like how everything is working then more power to you, but it's almost a certainty that you are burning significantly more fuel than you would be with the recommended materials.  If you do a fair amount of forging then the cost of the extra propane will probably exceed the savings of using plaster of paris in a short period of time even if it holds up well and doesn't fail in a way that injures you or anyone else.

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Plaster of Paris is reasonably insulating, but a poor bonding agent, mechanically speaking. The sand makes a reasonably tough grog, but is very poor insulation; result? A poor choice of "refractory."

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22 hours ago, Johnny Chesser said:

I’ve ran about 250-300 lbs of L.P through it

At our current price of propane, that's about $160.00 U.S. 300lb= 71 Gal @ 2.25 a gallon. Where are you located and how long did it take to use that much propane?

https://www.iforgeiron.com/topic/48833-read-this-first/

 

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Not to mention that Plaster of Paris starts to degrade around 450 deg F and we will be wanting to use it at over 1000 degrees higher temps!

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I've used the plaster of Paris and playsand mix in my 20lb propane forge. After about a month of use and not heavy use at all, the plaster degraded enough that I could not use the forge anymore. I tipped the forge up and it all fell out. 

 

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Ugh, just saw KORs pop/sand mix mini foundry come up on an instructables email. It just won't die. 

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Bad information keeps getting forwarded by people who do not know enough to know it's bad information.  It's the internet!

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We've been watching YouTube and I want to make a forge with my 11 year old grandson and don't want to disappoint him so if plaster of Paris is not the best thing to use what should I use? 

I planned on plaster of Paris and sand. 

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8 minutes ago, Trevor Colin said:

We've been watching YouTube

Watching youtube can give you some good general ideas to *think* about...believing youtube to be a good definitive source is where people get in trouble...sometimes dangerously so.  In the areas of forge building, probably about 90% of what's there is just people repeating what others got wrong.

If you look in the forums tab of this site under gas forges, you will find "stickies"...some excellent information that was pinned there to be helpful forever.  Among those in the section is a lot of peer-reviewed information on how one should properly build a gas forge. Sometimes it takes a while to sort through but if you dive in, it will start making sense.

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Welcome aboard. Have you read this yet? READ THIS FIRST If you edit your profile to show your location it will help with answers because many are location dependent.

I hope after reading this thread you have scraped the PoP & Sand. There are many discussions in the Forges 101 thread about lining a forge. Generally it's rigidized fiber like K-O-Wool or equivalence with a hard facing of castable refractory like Satanite or Kast-O-Lite.

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18 minutes ago, Trevor Colin said:

We've been watching YouTube and I want to make a forge with my 11 year old grandson and don't want to disappoint him so if plaster of Paris is not the best thing to use what should I use? 

I planned on plaster of Paris and sand. 

Trevor Colin, are you planning a propane forge? If not, may I suggest a charcoal forge based on Charles Stevens's JABOD (Just A Box Of Dirt).

A JABOD has a lot to recommend it---low cost and uses a lot of basic skills, such as digging clayey dirt, sifting clayey dirt, and building with clayey dirt. You can build one quickly and be forging the same day.  Fuel can be coal but to make it easy, get some lump charcoal from the grocery store (not Briquettes---that's the wrong stuff) that's actually made from wood. 

You can also use coal---like from a mine---but I'm not familiar with that fuel. There are a ton of people in the Solid Fuel Forges subforum, though, who use it and can guide you. What's nice about charcoal is that it's fairly easy to find and if you don't use the whole back, you can grill up some dinner.

JABOD forges are fun, and you get a real sense of how and why forges work the way they do. And you and the grandkid will find out really fast if blacksmithing is something you want to pursue.

Then if you decide you want to build a propane forge, there are a lot of threads on design, build, and safe use of these types of forges here.

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Plaster of Paris starts to degrade around 1000 degF below good forging temps.  It is also not an insulating refractory and so it drives up fuel costs.  Videos advocating it's use are indications that any idiot can post a video. Knowing how to sift the wheat from the chaff is the problem.

The thread mentioned will teach you how to search this website for answers; please read some of the comments to those answers as we ride herd on them and try to make sure that bad answers don't propagate.

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So, I just got back from Home Depot where I bought pop and play sand. Seriously, walked in the door fifteen minutes ago. Woe is me. I’m making a small foundry rather than a forge and want to case harden some steel. So what material should I use instead of the pop and sand?

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What do you want to cast? Aluminum,  Brass, Bronze, cast iron, steel, platinum, tungsten?  The material you cast  will control what you need to use as a refractory.  Probably kaowool like is used in a propane forge will work for you---properly coated of course---if you will be building a propane foundry!    What fuel will you be using?---Yes this is in the gas forge section but we have had folks make that mistake before too.  How large a foundry? How often will it be used?  It's difficult to give good answers when there are not enough details provided.   

BTW I'm off till Monday in a couple of minutes; others will have to help till then.

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I’m sorry, I just signed up and I didn’t realize there were different areas for different interests. I’m going to be using charcoal since I make it myself, and I’m going to be melting aluminum for prototypes and case hardening steel also for prototypes. 

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