Q.
I am building a kiln with double walls using 4” concrete blocks with some form of insulation between them. I do not have access to conventional insulation materials, but a friend mentioned that sawdust used to be used in buildings in New Zealand as a cheap form of insulation. Would it be suitable for insulating a kiln?
I might add that I am on an island in the Pacific, approximately six degrees south of the Equator so do not have the problem of winter temperatures, but have high humidity at times.
Whilst on the subject, would I be wise to apply a sealing coat to both sides of the bricks or would sealing the inside wall of the kiln and the outside of the exterior wall be sufficient? Should I paint the interior walls white to reflect the heat? Would painting the exterior walls black be beneficial, or is the wall too thick for that to matter?
A.
Sawdust must be dry to be a good insulator.
Sawdust will rot if the humidity is quite high, so when in a wall, you would have to make sure that it is kept dry -- no leaks! Tough to do.
Sawdust also presents a fire hazard.
Sawdust also settles, and the idea behind insulation is to hold air in a static, preventing movement. Settling would therefore, in both a practical and technical sense, render the top part of the wall uninsulated.
Overall, for a humid structure like a kiln, sawdust is not a good idea.
Seal ONLY THE INSIDE surface of the wall. This will allow any moisture that does happen to get into the wall to get out. DO NOT SEAL BOTH SIDES.
Painting the inside is not needed and will do no good from a heat standpoint. But, do seal the inside against water vapor, as mentioned.
Painting the exterior a dark color is O.K., so long as the paint will provide no resistance to water vapor movement. That said, with your high sun angles, such painting will not save much energy.
- Gene Wengert, forum moderator
