Can wood be too dry?

Re: Can wood be too dry?

John K Jordan

If the new environment has more moisture than where the wood was stored, the wood will absorb moisture and expand until it reaches equilibrium. It likely won't move as much as it would if starting out very wet but you will have to decide how much expansion is acceptable to your project if you decide not to let it acclimate.

You can use a wood shrinkage/expansion calculator such as this one to estimate the change: http://woodbin.com/calcs/shrinkulator/

For best results you will need to know the initial and target moisture content.

JKJ

no

Bill Tindall, E.Tn.

Short of heating it you will never achieve a moisture content as low as commercial KD hardwood lumber.

maybe, but unknowns

John K Jordan

He said "I have some oak that has been stored in a green house attached to my house for years." No other details. If this is a greenhouse not used for plants (and without moisture introduced) it might be a big heater assuming the greenhouse is in the sun, as common. That's why I implied it would be helpful to know the initial moisture content, unstated, but presumably by measurement.

If this is an active and steamy greenhouse the MC may even be higher than typical KD.

Perhaps Mr Irby will provide more information.

no unknowns of significance

Bill Tindall, E.Tn.

This greenhouse has not been hot enough, nor will it ever be, to get wood to 7% MC unless the outside humidity plunges lower than it normally gets in the VA on a summer day.

Re: no unknowns of significance

Barry Irby

This is a solar heating green house. I got interested in super insulating houses and providing solar heat back in the late 70's. This green house is on the south facing wall and is two stories tall. It used to include a water heater but that is defunct. The sun shines in and heats the area about 60* above ambient and small fans circulate the heat into a storage system that included hundreds of gallons of water. In the summer some of the glass can be replaced with screens to allow the heat to escape. It also relies on sun angles to avoid over heating.

I had long since forgotten what wood was in there but today I pulled out some oak and it meters 6% which is as low and the meter will measure. It's a pin type meter, a Wagner I believe.

The wood was air dried when I put it in there. Somebody gave me the wood and I think I may have overpaid.

Re: no unknowns of significance

Bill Tindall, E.Tn.

Pin meters are not accurate at low moisture content.

There is no way this lumber is 6% this time of year. To get to 7% moisture content commercial kilns are run at 170 F (+/-) at the end of the drying cycle.

If the true moisture content of "dry" lumber is needed it needs to be measured by drying to constant weight at 215 F and measuring moisture loss.

I do believe you could get lumber this low in the summer though with a succession of sunny days and moderate humidity. But you will never get it "too low".

Re: no unknowns of significance

Barry Irby

Thank you for your thoughts. I have dragged out some of the wood and started prepping it to make a toybox for my granddaughter. If there is any problem with it from drying, I can't detect it. Unfortunately, there was no magic during storage. It's still got the same knots it had when I put it in there.

Re: no unknowns of significance

kneale brownson

But knots can be very pretty!!!

Re: Can wood be too dry?

Johanna Johanson

I hope not! Our relative humidity often drops into the single digits and rarely exceeds 30%, so my stash of lumber is really, really dry. I just looked at our weather device - right now the humidity is 4%.