For many years furnituremakers have preferred building with air-dried lumber over kiln dried lumber. Among its reported benefits are more brilliant color, improved workability (both with power and hand tools), and its superior suitability for steam bending — because the wood’s lignin remains permeable. I recently stacked a shipment of roughly 500 board-feet of curly, quarter-sawn white oak, and thought this a good time to talk about it. In this post I’ll focus on how to prepare, stack and monitor your lumber.
I have a small concrete plat behind one of my out-buildings that I use for stacking lumber. You don’t need a concrete plat, unless perhaps you live on a bluff and erosion is a problem; otherwise bare ground is fine, just remember to place a sheet of plastic between the ground and lumber stack to isolate excessive ground moisture from the stack. Also if you’ve recently poured your concrete plat, give it about a year to cure–it will take that long for the moisture to stabilize.
At a macro-level air drying lumber is a two-step process. First dry the lumber outside until it reaches equalization with the moisture content of the outside air. Depending on what part of the country you’re in, this will be somewhere between 12 – 15%. Then move the lumber inside your shop to dry it to a furniture making level of approximately 6- 8%.
Begin by establishing a good based and solid foundation for your wood stack. Ideally you want your base flat and level. I choose to go with flat at a slight incline to ensure water does not inadvertently pool on my stack. Having a flat stack is a must because green wood is relatively pliable and the sheer weight of the stack can mold boards on the bottom to the shape of your base.
I use a layer of cinder blocks with 2 X 4 beams going across them for my foundation. Place these 16″ – 24″ apart. The normal rule of thumb is 16″ for softwood and 24″ for hardwood. The 2 x 4s are two lengths screwed together to essentially form a 4 x 4. I cut a dado down the center of the 4 x 4 to hold a sticker halfway proud of the beam.
Don’t chinch on your stickers. Make them from dry wood and ensure all are a consistent size– mine are 3/4″ x 1 1/8″ x 48″ for this stack. Consistent stickers help ensure a properly built stack that transmits the bases flatness throughout the stack.
Now your ready to build your stack. Putting wider boards on the bottom serves the dual purposes of helping keep them flat and making a more stable stack. To help facilitate air movement through the stack, establish gaps of at least 3/4″ between board edges in the layers, and stagger the gap locations from layer to layer to increase the stack’s stability.
After the wood is stacked seal the ends with AnchorSeal to help prevent end checking. Currently there are two types of AnchorSeal available–Classic and the newer, environmentally friendly AnchorSeal2. I still use classic AnchorSeal because so many people are voicing complaints about the green version. I asked UC Coating about this, and the said, it is primarily turners who are seeing problems with AnchorSeal2. Classic AnchorSeal is getting hard to find, I buy it directly from UC Coating. They will still sell a five gallon container to small shops.
With the AnchoSeal applied, add a top that over hangs all edges by 1- 2″ to protect the stack from direct sun and rain.
With the wood stacked and covered, you’d think you’re done; but actually building the stack is the easy part. I believe monitoring is the more challenging part. Monitoring involves answering some key questions, namely:
- When is the drying complete?
- How do I know if my stack is drying too fast?
- What do I do if it’s drying too fast?
- How do I know if my stack is drying too slow?
- What do I do if it’s drying too slow?
The first question is easy–since I addressed it earlier. The outside drying step is complete when the board’s moisture content is equalized with that of the surrounding environment’s relative humidity. An Equilibrium Moisture Content (EMC) chart will help you determine this, and a good moisture meter will allow you to read the board’s moisture content.
Your stack is drying too fast if end-checks and care hardening develop. Most of us understand checks because, sadly we’ve seem them at the lumber yard when buying lumber. Case hardening is bit more complicated and you can consult one of the resources at the end of this post to get a more in-depth understanding of it. To slow down the drying process, anything you can do to slow the air movement through the stack is the answer. adding a curtain of ShadeDRI material on one or more sides of the stack will retard air movement.
Your stack may be drying too slow if mold or fungi develop. A stack that is drying too slowly also increases the likelihood that wood-boring insects may attack. Accelerating the drying process is more challenging than slowing the process because the speed of drying is limited by the surrounding environmental conditions (i.e.: temperature, relative humidity, and wind). Thus to increase drying, take steps that will maximize these conditions–increase pile spacing (between individual boards and layers); open up the piles foundation, or utilize a fan to increase air movement through the pile.
Fine Woodworking has several good article on air drying lumber. See issues 2, 151, and 204, or search their online magazine index.
For some more in-depth reading on this topic look at these resources:
- Air Drying Lumber; US Department of Agriculture, General Technical Report (FPL-GTR-117)
- The Encyclopedia of Wood by US Department of Agriculture; 2007 Skyhorse Publishing, Inc.; New York, New York
- Understanding Wood: A Craftsman’s Guide to Wood Technology by R. Bruce Hoadley; 2000, The Taunton Press, Inc; Newtown, CT