Solar kiln out of natural materials

Looking to build a solar kiln for drying slabs of lumber (2-3 inch thick pieces) and The plans I’ve seen online all have plywood, foam insulation, and pressure treated lumber. Anyone made one that was rot resistant with correct airflow using natural materials?

Oh - especially wondering about sealants; the kiln plans all include rubber. Or aluminum paint. Non toxic heat stable alternatives?

Lina, I think you could adapt a lot from the solar dehydrator plans, there was special effort (since drying food) for it to be free of toxic gick.

As far as sealing, using boards with "shiplap" or "tongue and groove" edges would be better than plain boards, and except for excluding rain, I don't think perfect sealing is imperative (it may just cut into the efficiency a bit).

I think folks jump to pressure treated lumber for durability/longevity for moisture and ground contact, but really a kiln is a temporary sort of structure (not like a house) and could be built on replaceable skids (like the dehydrator) and following good practice such as elevating it off the ground (on stone or concrete blocks) overhanging roof (to shed water away).
The same goes for rubber. I've seen a design with a curtain hung over the wood to create the airflow through the stack of lumber, seems as if this is where you are seeing rubber used? Maybe canvas would work? old wool rugs? or an adjustable wall made of boards stacked on edge between channels on the walls?
Insulation? maybe to boost cold weather performance? could be overcome by having more solar collecting area than just the kiln area?

Kenneth Elwell wrote:Lina,
The same goes for rubber. I've seen a design with a curtain hung over the wood to create the airflow through the stack of lumber, seems as if this is where you are seeing rubber used? Maybe canvas would work? old wool rugs? or an adjustable wall made of boards stacked on edge between channels on the walls?
Insulation? maybe to boost cold weather performance? could be overcome by having more solar collecting area than just the kiln area?

Its not the curtain: the plans I’ve seen are all big on painting the inside with a sealant paint - either rubber paint or aluminum paint. I think because it is a very moist environment for months at a time, they are designed to keep moisture out of the walls. Now, I suppose that since the wood you are putting in manages to dry out, the wall would too - but it seems like if everyone thinks sealing the inside is a good idea, there might be a reason. But maybe not?
Insulation - I suppose it is in part for cold weather, but also to maintain a more even temp throughout the kiln, I think. The problem with L expanding the roof area is that, as I understand it, the area of clear roof to board feet is calculated pretty carefully to dry the wood at a safe rate. The plans here https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/420/420-030/420-030_pdf.pdf include the ratio, and directions for different board types. So increasing the ratio might crack your board. On the other hand, maybe just not insulating would do ok, just lead to longer drying times.