Kiln wash beading up

Sometimes kiln wash does not seem to want to stick to the mould.  There are several possible reasons. The main two seem to be a hard spot in the slip cast moulds that we use.  Another is the previous use of boron nitride or other sealant of porous surfaces.

The remedies are different for these two causes.  For hard spots you can add a bit extra kiln wash to the area.  Normally enough separator adheres to the spot to avoid sticking.  This is so even though you can see the spot more clearly than the rest of the mould.

Sealed surfaces present a little more difficulty.  It is possible to carefully sand blast off the boron nitride from the surface using low pressure and very little abrasive.  This works well for textured surfaces, if you are careful.  You can also manually sand the sealant off which works better for regularly shaped smooth surfaces.   The object of both these processes is to remove the sealed surface to reveal the porous material again.  You must remember that you are removing some of the surface of the mould in these abrasive processes.  Once removed kiln wash can be applied as before.

If neither abrasive method works, it does not mean the mould is ruined.  You can continue to use boron nitride.  Or, if you want to avoid the costs of boron nitride, you can sprinkle fine dry kiln wash over the mould.  You should give the mould a final application of boron nitride before using the dry kiln wash.