[TheForge] Gas Forge Plans - a question

[Andrew Vida]

Bruce Freeman wrote:
> Spalling is usually caused by volatile components in the brick.  Get these hot enough and they explode into vapor.
> 
> The classic volatile componet is water, but carbonate (i.e., portland cement) is another.  
> 
> Dry your bricks, firebricks, castable refractory, etc., etc., THOROUGHLY before firing your forge to forging heat.  One way to do this is by building a wood fire inside the forge, but if you can control your propane burner at a low heat, that works too.
> 
> The suggestion I've heard is to bring the forge to a dull red heat - SLOWLY.  I doubt that temperature is really necessary.  

	With ceramics, there is a period called "water smoke" where the kiln is 
left open and the elements fired to slowly raise the temperature to a 
bit under 300* F.  By the time it gets to that temperature one is well 
assured that all moisture has been removed.  If you don't do this, you 
risk dunting or blowing the work (ceramist-speak for cracking and 
spalling).  A slow rise to 300* will guarantee all moisture is gone, 
with the emphasis on SLOW, as Bruce put it.