Air drying question?

[Richard Bazemore]

Back in April I stickered a bunch of Oak in my detached (generally unheated) workshop, on the concrete slab floor. I had heavy plastic down first, then a row of ¾” stickers, then alternating the 1” thick boards and more stickers. Nine layers in all. Size of stack was about 12-14 feet long, 8 feet deep, and 1 ½ foot high. Maybe an inch gap between adjacent board edges. Topped of with about 12 cinder blocks to try to keep top boards flat.

This weekend I unstacked the pile to load the boards onto my wall mounted lumber rack, and found that the bottom two layers had what appears to be surface moisture on the top face – a large, circular water stain centered on the top face of the stack, covering about 80% of the surface. Black mold had formed in this region, felt wet to the touch. Looks like surface moisture since some clearly traveled around the edges and stained the bottom of some boards, in some places.

There was no “spill”, roof doesn’t leak, etc. Top 7 layers were dry. Moisture content of top boards was about 9%, but on the bottom layers it was 12% (pin-type meter, sampled about 3/8” down).

Where did this moisture come from? Moisture leaving boards above? Is this typical of air-dryed stacks? Is it reasonable to close stack the boards with the wet surface and mold at this point? Do I need to sweat the mold?

[lou sansone]

richard

I air dry all of my lumber and I usually keep it off the floor by at least 10 inches. It seems that the closer you are to the earth the more "damp" you can pick up from the earth, eventhough you had the plastic down. There is a specific forum at "woodweb" on sawing and drying where there are hundreds of real knowlagable folks that can give a much better answer then I can.

[Charles Hans]

It sounds like you needed more air circulation,as well as it was too close to the ground. have you checked a piece to see how deep the stain penetrated?
Chuck

[Richard Bazemore]

Charles - That's a good idea, I'll cut into one and see.

[Karl Laustrup]

Even though you had plastic down, I think the main problem was height off the ground. I was told when I did my first stack for air drying that I should put down plastic and then the stack should be at least 12" off the ground. It also sounds like a lack of air circulation could have been a factor.