I'm making a coal forge for blade smithing, one of the simple galvanized tub ones (credit to Tim Lively).  

I am also making a kiln out of an old helium tank, and plan on lining it with the same materials.

I have some H.C. Muddox Fire Clay Mortar from Home Depot.

So, my question is, I don't think that this mortar was intended for lining forges, more like for lining fire place bricks and such.  Do you think that the original recipe that it suggests for this mortar will work given the high temperatures for a coal forge and a coal kiln?

The directions say: 1 part fire clay mortar, 2 parts cement, 6 parts masons sand

Questions:

1.  Would the directions mix above still work for forge lining?

2.  What cement type should be used?

3.  Do you think there would be much shrinkage? (there was a ton of shrinkage when I tried a 1:1 mortar/sand mix, I'm guessing that the fire clay shrinks a ton by itself as it dries)

 

Thanks!

-T

 

 

You can line the washtub with clay rich soil straight from the ground. Just get all the rocks out. You know that when heated galvanized coatings release zinc oxide which is toxic?  You might want to remove the coating on the tub. I don't know if it's going to get hot enough to release fumes but better safe than sorry.

Pnut

You can mix three parts sand to one part clay to make the lining. Your choice of fuel will make a difference as to how well the forge works. Charcoal likes a sideblast forge. Bottom blast forges burn up charcoal very quickly. Coal will work in side or bottom blast forges equally good. You could make a great sideblast jabod out of your tub. You should look at the jabod threads in the solid fuel forge section.

Edited August 17, 20196 yr by pnut

6 hours ago, colafran said:

1.  Would the directions mix above still work for forge lining?

2.  What cement type should be used?

3.  Do you think there would be much shrinkage? (there was a ton of shrinkage when I tried a 1:1 mortar/sand mix, I'm guessing that the fire clay shrinks a ton by itself as it dries)

1) No, it won't work. Use typical clay soil and sand as Mr. pnut has stated for your washtub forge, and a commercially available refractory for your kiln. I don't have enough knowledge about kiln applications to suggest a particular one. There is a refractory subforum inside the gas forge forum, and I suggest that you look there. 

2) Don't use cement at all unless you want it to spall when the water bound to the concrete turns to steam. When it spalls, expect hot cement and burning fuel thrown on you at high speed during the steam explosion. 

3) See the answer to (1) 

 

I would also like to recommend that you use a piston (made from any round metal piece that fits your pipe somewhat snugly) rather than the end cap to seal your air pipe. You can move the piston in and out to control how many holes are blowing into your fuel, and therefore have a variable fire size. 

I know you have been around for a while but, have you read this yet? READ THIS FIRST

I second what pnut & Chris have posted. Your side blast wash tub forge will probably be ok for a while but for the kiln you will want to line it with Kaowool ridigized (at least 2 inches) and use a refractory like Satanite or Kast-O-Lite 30 (available from this forum). The kiln needs insulation.

https://www.iforgeiron.com/forum/257-insulation-and-refractories/

If you haven't yet mixed up the fire clay mix, just eliminate the cement and it will be adobe which will work better. If you have already used the cement mix just replace it with adobe when it falls apart. I noticed that the picture you posted is from Tim's post about building the forge.

Thank you all!  Exactly the right information I needed.  You guys are great.

Another note, that is specifically a knife forge. Even for knives you don’t need the long trench exept for heat treat. 

I typicaly recomend a simple side blast forge. It is simpler and more fuel efferent.