Kiln Wash Crust

[rpastore]

I have done about 10 firings on my kiln and have not always needed to put kiln wash on the shelf each time. My last firing which was a bottle slumping put some indentations in the kiln wash when the bottles were removed and made it uneven. I tried to clean all of the wash off the kiln shelf and redo it but had a hard time removing it so I decided to flip the shelf over and use the other side.

So I don't build up a "kiln wash crust" again, I am wondering if I am supposed to completely clean the kiln wash off after each firing and reapply?

[Laurie Spray]

You can get quite a few loads done with one application of kiln wash. When it starts chipping off it is time to remove it. I use a hand sander with rough sand paper until it is completely gone. The shelf just gets smoother and smoother. Be sure to wear a mask. It can be a dusty job.
When doing something extra hot like pot melts I sand it down with each firing and reapply fresh.

[Kevin Midgley]

drywall sanding mesh

[Bert Weiss]

The hotter you fire, the less durable is the kiln wash. Keep your firings under 1400ºF, and it will last a very long time. I advise at least a thin fresh coat after you have fired over 1400. Many times you can get away without this, but sometimes a white scum is left. I hate it when that happens. As others said, when you fire hot, you want a good fresh coating. After it has chipped, the only way to get rid of the ridge is to remove it all. I like Kevin's open mesh sanding screen as the most effective abrasive that doesn't get clogged up.

I use a bit different strategy. For firings above 1400, I make my own kilnwash mixing about 80% finely ground alumina hydrate with 20% EPK, by weight. This mixture is pretty easy to clean off each time. I work primarily with float glass, which requires a thinner coating than the fusing glasses. When I work on hard shelves, I usually paint a pattern on with my kilnwash which leaves a decorative imprint. For most of my flat shelf work, I fire on fiber board that has been dusted with alumina hydrate, and no wet kiln wash. Much of my work is done on the kiln floor with either a sandbed or powdered fiber blanket. These are the easiest approaches for me, in my kilns.