clay linning

[kenG]

This is just the first of what I'm sure will be hundreds of beginner questions. I appreciate the warm welcome and the willingness to help.
This is the little portable forge I picked up. It has "clay before using" cast into the metal. I hope I'm interpreting what I have read in the archives correctly and it is ok to use without the clay linner. What are the reasons for linning with clay and what will it hurt to not line it?

[Mlmartin15]

the clay acts as a buffer between the metal and the coal fire, the fire will be so hot that it will heat up the cast iron firepot quick and its vary likely to crack and break. ive seen many people just use old red clay right out of the ground or any other clay they can get there hands on, im sure there are better clays ment for this, but i dont know them, and ive seen the pot covered with clay about as thick and half and inch up to about one inch. just line the firepot, or the bowl that the fire sits in, let the stuff dry for a day or two, then start a pretty small fire, and let it burn for a little bit to dry out the clay. if ya dry it out to fast it will crack off, but its just clay so no worrys

this is just what i have herd and exsperanced, im no expert, just my thoughts on the matter
good luck and happy forging

[hill.josh]

the clay is like an insulator and it protects the iron from burning up and then needing to replace it, ive used clay from a river, mud from my back yard, and then a mixture of portland cement and sand where it was 3 parts sand to one part portland cement and some water(enough to make it feel like fairly wet mud). the last of the 3 is defiantly the strongest against knocks. the mud eventually falls apart but is easily replaced and is free. ive heard that portland cement will spall but its never happened to me and is what i use right now.. not saying it won't spall but just that it hasn't happened to me. don't go on what i say though just cause i said it.. do what you think is safest.

[hill.josh]

my firepot is actually made completly of portland cement/sand so I don't know what would happen to an iron firepot if it would crack or not.. i haven't heard of that i just know that iron will burn up.

[kenG]

Josh,
When you say Portland Cement, I assume you are talking about type I Quikrete like Ace sells? and just plain ol' sandbox sand mixed together? That's simple enough.
Thanks,
Ken

[dablacksmith]

i have used forges with out lineing them ... if you heat them up quick you can cause the cast iron to crack .. its a expantion thing i think . anyway clay the bottom but leav it thinner towards the grate and expect clinkers to stick to it occationally.

[Meisenmann]

An additional bonus if you clay your forge:

Better Insulation and less coal usage, therefore saved money.

Build a small roof from "autoclaved aerated concrete", very cheap stuff but it works. Therefore even better heat retention and you can better judge the colour of the steel.

[philip in china]

Mix some coarse sawdust (chainsaw dust is best) with ordinary clay out of the ground. The sawdust burns as soon as you light the fire. This gives little air pockets which greatly increases the insulation value of the clay.

The local smith here just picks up clay from the ground. He is 81 and has been smithing since his teens so probably knows something!

[jimbob]

I believe the clay acks as a buffer from coal as a lot smithing coal has sulfur in it and when you add water to to coke it the sulfuric acid leaches out and will rot the cast Iron pot/bottom/firebox out. Its myunderstanding that cast iron resist corosion better than steel...whence one of the reasons for the cast iron forge as apposed to steel

[rmcpb]

I just line mine with a mortar mixture like used by brick layers to fix bricks into position. Simple, cheap and if it breaks then easily fixed/replaced.