Kiln Washing Kiln Surfaces

“Having just got my first kiln, I was wondering how often I have to add kiln wash to the bottom of the kiln.”

It has become common practice to kiln wash the bottom of a new kiln.

This may be fine for brick lined kilns.  Kilns with fibre blanket or fibre board do not need to be kiln washed at all.  The fibre is a separator already and does not need additional material which will turn to powder and need to be carefully cleaned to avoid damaging the refractory fibre lining.  This has led me to reconsider the value of kiln washing the bottom of the kiln.

I have followed the practice kiln washing of the bottom of the kiln in the past.  However, I have found that small glass pieces falling to the floor, do not stick to the bare brick or to fibre.  They can be vacuumed or picked from the surface of the kiln without creating any damage.  This means that at fusing temperatures, the brick and fibre does not stick to the glass and kiln wash is not needed.

The main idea seems to be to help protect the kiln surfaces from the molten glass if a relay becomes stuck, raising the kiln temperature to very high levels. Kiln washing the bottom of the kiln does not protect the brick or fibre from a large amount of glass running off the edge of the shelf onto the bottom. Of course, pieces of glass resting on the floor of the kiln may become stuck when higher temperature work is being conducted, such as combing, the various melts, and casting.  The solution is not to kiln wash the floor, but to clean the floor of the kiln before entering the high temperature processes.

There is not really a need to kiln wash the bottom of the kiln at all.  The kiln wash will not protect the kiln brick or fibre in the event of a high temperature accident.  The kiln wash turns to powder which needs to be cleaned from the kiln to avoid contamination, as with other dusts, of the glass being fired.  The main objective is to keep the kiln clean and free of dust rather than adding another source of dust.  A dusty atmosphere in the kiln can promote devitrification, so anything which avoids introducing dust will be beneficial in reducing the incidence of devitrification.

I suppose if you really want to protect the bottom of the kiln from molten glass, you can add a high temperature separator such as a refractory fibre board, or a thin layer of sand.  The sand will resist the molten glass and can be scooped out of the bottom before adding new. 

After some consideration, I no longer think kiln washing the bottom of kilns is worth the potential for dust accumulation, as it doesn’t really protect the kiln floor during high temperature accidents. Low temperature spills of frit, glass powder and shards will lift off the kiln surfaces easily without damage to surfaces.