Hi all - I have just finished drying my first load of lumber (4/4 black walnut). My little kiln seemed to do a nice job. Now I have a few hundred board feet 7% lumber and am concerned about bringing it out into the 60%humidity (18% moisture content) ambient environment.
Should care be taken when reintroducing dry lumber back into a "normal" atmosphere?
And is kiln drying to 6-7% necessary or is air drying to 18% (seems that's where we are in the Great Lakes region) okay?
Thanks for any thoughts/experiences,
Jeff
From contributor Do
Is the space unheated? If the space is heated in that area, it is unlikely to be 60% this time of year.
From contributor Je
HI Don, the space is an airplane hangar. So it is semi heated, I have a weather station installed and believe the data it is reporting. I only have it heated to 50 F and the humidity will vary, it's been in the 60% range as of late.
From contributor Do
at 50F and 60% RH the EMC is about 11 so the lumber will gradually try to come into equilibrium at that MC. If you downpile it and wrap it well, you will slow the process down. If there is a sunny or warm side of the hanger, put the lumber there. If you wrap it, I doubt you would see more than 1% per month increase in the winter.
From contributor Ge
The outside humidity in the Lake States, not really close to the water of one of the Great Lakes is 65% RH average which is 12% MC in lumber, so we call it 12% EMC conditions of the air. Your data of 18% is not correct.
It would be unusual to find a Ludington that is heated slightly at 60% RH. Heat quickly lowers the RH. For example, heating foggy, 100% RH air by 25 degrees F results in 30% RH. This is why storage facilities are really good if heated 20 to 25 F above the morning low temperature. The EMC will be around 7% EMC.
A kiln can dry to whatever MC you want. Most wood for interior use is dried to 6.0 to 7.5% MC in a kiln as this is the MC that wood will have in use inside a home or office.
Ok?
From contributor Je
Thanks guys, I have a lot to learn. I came up with the 18% moisture content by pinning the lumber that's been in the hangar for ever.
I'll increase the temp in the hangar until I can move the lumber to a better location.
Thanks again,
Jeff
From contributor Do
if you only heat the hanger to keep things from freezing, you might add a humidistat to also run the heat when the humidity is over 35-40%. The humidity drops as the temperature goes up. So lets say it is 50F and 60%, the humidistat would bring on the heat until the temp was about 65F. Then the EMC would be fine. You need to pay attention in the summer so it doesn't get too hot. This is not a great idea if you have people working in there regularly because the changes in temp will drive them nuts.
From contributor Ge
The pin meter is giving you poor readings. Not sure why. Who is the manufacturer? If Delmhorst, it should have an internal calibration check or send it back to NJ for a quick inspection. Do you get a reading even when the pins are inserted? Was the wood you tested treated wood? Can you test some wood in your home like the bottom of a table...about 7% MC?
From contributor Je
I think the moisture meter is fairly accurate. It's made by General. I primarily heat my house with wood so I pump humidity in as best I can. RH in the house reads 49%% right now. I have pinned wood in the house in the past and I recall it read about 12%. For now I think I'll pull the load out of the kiln, stack it, cover it and keep an eye open for a better storage option - or get it on Craigslist and sell it.
Thanks again, loading Maple next.
From contributor Ge
At 50% RH, you should see 9% MC. It takes 65% RH to get 12% MC, and that is the outside average RH in your area, but inside will be lower indeed.
I do not know the company that made your meter, but it does seem to be reading quite a bit higher than the true value.
From contributor Je
Thanks, I'll check into the accuracy of the meter. I have seen a table of RH-MC but don't recall where I saw it. Do you know where I might download one?
From contributor Ge
100 megohms is 12% MC. Maybe you can buy a resistor to put across your pins.
0% RH = 0% EMC
30% = 6%
50% = 9%
65% = 12%
80% = 16%
100% = 28%
More detailed values are often not needed, but are in Drying Hardwood Lumber about page 16. Download here at WoodWeb
