How long?

DixieReb31 · February 02, 2022, 02:07:02 PM

I have a 40'x60'x12' pole bldg I use for my sawmill and air drying lumber. It is open all the way around. It faces exactly due east. So the south side gets sunshine all day inward to about 10' before the roof shades the rest. So, I stack green lumber to air dry on the North side. Never any sun on that side. I live in SC so most of the SYP will only air dry to around 13%ish. But, my question concerns hardwood. If hardwood is dried down to 6-8% in a kiln, how long being stacked in an open building will it take to regain air moisture and go back up? I do not have a climate controlled building to keep hardwood in, I'm wondering if it's worth my effort to build a solar kiln if I can't control the moisture after it's dried.

WDH · February 02, 2022, 07:02:22 PM

The wood exposed to the outside air will begin gaining moisture immediately. If stickered, that will increase the rate of moisture gain substantially in the boards. If flat stacked, the outside boards will gain moisture and the moisture will slowly migrate to the interior, but it will take much longer.

If you leave it flat stacked and cover it tightly with waterproof plastic, that will significantly slow down any moisture gain.

rusticretreater · February 03, 2022, 12:42:09 AM

Its always worth it to build a solar kiln. Why would people do this if it wasn't?

Air drying only removes moves the easily discarded moisture from the wood and there is an imbalance of moisture from the exterior to interior. Kilning is the only way to remove excess interior moisture from the wood in a reasonable time frame and also to eliminate surface checking and other defects. It is recommended that samples taken from a stack of wood being kilned be cut open to check the interior moisture content. The moisture testers used on the surface of the wood penetrate only so deep.

It is better to have a board with a dry core and an exterior that might gain moisture compared to a board that is wetter inside and drier outside. As the wetter board dries, it does so in an uncontrolled manner leading to warping. A drier core makes a board much more stable and the wood won't move around even as it gains moisture content from the open air. The stresses are much different.

Kilning leads to higher yields from all your work. Kilning also kills bugs, fungus and mold. In areas where there are quarantines on transporting of untreated wood, kilning is the only way to get wood treated well enough to be granted certification of compliance. You can also use your kiln to treat firewood.

You mentioned a climate controlled storage area. What about when the wood is used for some purpose? Is the shed that's built with it also going to reside in a climate controlled area? Wouldn't it be better to have the wood acclimated to the environment and allow you to cull the problem boards before they are used in a project?

DixieReb31 · February 03, 2022, 06:42:08 AM

The wood I was referring to when I mentioned climate control, was any hardwood. Most hardwoods are use for interior projects that will be in a climate controlled environment. I would not want a project to start busting joints because the wood regained enough moisture to do so. Construction lumber is a different matter and I am satisfied it being 11-15%. I think wrapping kiln dried lumber in plastic would be my best bet.

GeneWengert-WoodDoc · February 03, 2022, 10:47:50 PM

If. You wrap all six sides of a load with plastic and do not make many holes, you can store it for many months.

Ianab · February 04, 2022, 12:01:10 AM

I don't know Exactly how fast wood will pick up moisture, because I'm sure that varies as much as drying time does. But from my own experiments with "oven drying" wood samples, White Cedar went from 0% to ~13% in about 2 weeks, sitting on my desk . Weighed each day on a digital scale. Say one week from 8 to 13?

I'm sure hardwood would be slower, same as it's slower to dry, but you would still measure it in weeks.

Gene's comment about plastic is correct. If you can seal the pack, then there is almost zero moisture transfer. Like a pack of biscuits, they will last a year if the pack is sealed, but open it up and they go stale in a week.

Condensation isn't an issue because there is no "free" moisture inside the pack. As long as the rain doesn't get it, it will stay dry in there.

YellowHammer · February 04, 2022, 08:14:03 AM

It will move up pretty quick, a few weeks. Not only that, but it exposes the wood to insects and other bad things.

Depending on quantity, and your machinery for lifting and moving wood, even a shipping container or Connex is a good place to store KD wood. Typically, even with a little sun, they will be slightly warmer than outside temps, and so do a pretty good job of keeping dry wood dry.