Why shouldn’t you apply kiln wash to the underside of the lid and shelves or to the kiln walls?

Kiln wash is made of minerals that do not fuse at high temperatures. When applied to a kiln shelf, the kiln wash helps prevent dripping glaze from embedding into the shelf. Kiln wash is designed for easy removal from the shelf so that when glaze sticks to it, the kiln wash can be scraped off. For this reason, kiln wash is applied to the underside of shelves and the lid can flake off and fall onto the ware below. It can also flake off and fall into an element groove. Kiln wash can destroy a heating element. This is why it must never be applied to kiln walls.