Kaolin vs. Fireclay

[lwalper]

Kaolin is readily available and inexpensive at my local farm supply store. It appears to be chemically equivalent to fireclay (aluminum silicate) and is the primary ingredient for porcelin. Could kaolin be substituted for fireclay in the mortar mix. I've used kaolin as a pond sealer - get it wet and it sure is gooey stuff. Should make a very smooth high temp mortar??

[david s]

Probably is ok. It is more expensive for us in Australia. Another name for kaolin is china clay. Check its shrinkage properties. It might have a higher shrinkage rate than fireclay. All clays shrink and this can either be a disadvantage or advantage depending what you want the stuff to do. I use kaolin sometimes because it's white and sometimes because it helps improve my slipcasting mixtures.