Kaolin vs. Fireclay

[phatdaddy]

I made my firepot to deep and I'm wanting to shallow it up. My question is, what would be better to use, kaolin clay or fireclay ? I can get tons of kaolin for free and would rather use it if it will hold up to the heat. If kaolin will work, will I need to add anything to it?

[pkrankow]

On 10/7/2010 at 10:38 PM, phatdaddy said:

 

 

Kaolin is more durable, but needs fired high enough to vitrify. You may want to add grog (finely broken vitrified kaolin) to prevent cracking. Smash up some old porcelain to add. Wash the toilet before smashing though.

Fireclay will work fine too.

Phil

 

[MattBower]

Yeah, it's not too critical. Whichever one you can get will work. They're both pretty high firing. Clean, whitish play sand makes decent grog, too. (The darker the sand the more impurities it contains, and the lower it'll melt.) Try to use the absolute minimum amount of water in mixing up your clay; it'll dry faster, and it'll be less likely to crack during drying.

[phatdaddy]

I mixed some kaolin with some mulcoa dust for a little experiment. It didn't turn out like I wanted. I'll try the playsand next time, thanks for the help. I thought the mulcoa dust would work because I'm told at work that mulcoa is used to make firebrick. Oh well, the white sand and/or porcelin sounds good to me.The worst thing that can happen is it will crack and break loose, I'm getting everything from work (spillage from the conveyor belts) so I'm not out of any money.

[MattBower]

I would've expected the Mulcoa to work really well, actually. What went wrong?

[pkrankow]

Since it is dust I bet he had to add more water than he wanted. Fine dust won't wet nice at times. Mulcoa looks like primarily alumina and silica with some other oxides, and no obvious water friendly molecules, so putting in a covered bucket with a small amount of water for a few hours may get better mix than trying to mix it in one go. Then add the kaolin powder to the moist mulcoa and let sit again.

Probably the exact opposite process the plant uses.

From grogging kaolin with zircon flour (about 70%) I can tell you that 30% kaolin is adequate to get a stable ceramic. Zircon doesn't participate below 3000F, and I am not sure my forge gets there even! I also made a coating for kaowool, not a liner for a solid fuel forge.

Phil

[clgill57]

I am told you should seal up the loose fibers of the Kaowool with a layer of Castable Refactory  poured over the top.

Breathing Ceramic fibers is harmful

[pnut]

As stated above, it's not too critical. You could use clay soil from your backyard. My whole firepot is clay soil I dug up and it works just fine for me. It vitrified after the first forging session and I haven't had to repair it. It's been about three or four months. If you do use kaolin a grog would be a good idea. You probably already know this since you work with it everyday. We used to add quite a bit of it to the batches of rubber at the refinery I used to work at. About one third of the weight of the batch would be kaolin clay depending on which compound we were running.

Even using the kaolin you will eventually have to replace or repair it. A liner is a consumable it's just a matter of how long will it last before you have to fix or replace it.

Pnut

 

Edited June 26, 2019 by pnut

[ThomasPowers]

Clgill57; this is the solid fuel forge section. Solid fuel forges generally do NOT use fibrous refractories as they are not needed; so what you should have been told is "Don't use fibrous refractories when building a solid fuel forge! They have been building them just fine for around 3000 years without them."

[Irondragon Forge ClayWorks]

Welcome clgill57... have you read this yet? It will help you get the best out of the forum. READ THIS FIRST

Also this thread is 9 years old so I doubt any of the op's will see it.

[clgill57]

On 6/26/2019 at 11:24 AM, ThomasPowers said:

Clgill57; this is the solid fuel forge section. Solid fuel forges generally do NOT use fibrous refractories as they are not needed; so what you should have been told is "Don't use fibrous refractories when building a solid fuel forge! They have been building them just fine for around 3000 years without them."

But 3000 years ago they didnt have THIN CAST IRON fire pans that crack if you dont insulate them ..... I'm going to at least CLAY mine before I EVER build a fire in it  thanks for the heads up 

[Steve Sells]

After you build a fire, you will notice the fire pot never gets very hot.   Neither of mine have any clay lining, my main is 3/8 inch diamond plate, and 10+ years old and the portable is cast iron rivet forge,  still good after 30+ years just with me. Clay wont hurt, I just I dont see a need for it.    Fiberglass is useless for fire pots.