20 Steps to Drying Hard White Maple
The Wood Doctor's 100 percent guaranteed, sure-fire, no-snake-oil method for successfully drying hard white maple. 1998.
by Dr. Eugene Wengert
Professor and Extension Specialist in Wood Processing
Department of Forest Ecology and Management
University of Wisconsin-Madison
To successfully prevent enzymatic oxidation staining, it is necessary to dry lumber quite rapidly and to avoid high temperatures, especially above 40% MC. In the case of sticker stain, this prescription means drying the wood under the sticker as rapidly as possible. Certainly, when possible, the logs should be freshly harvested, especially during warm weather. When this cannot be done, then the following procedures should be followed. In some cases, the different measures suggested below may be excessive, but one cannot judge in advance the risk of stain formation. Therefore, doing a little extra should be viewed as insurance. The risk is staining the lumber, which can result in 1000's of dollars in lost income.
1. In warm weather, always use freshly harvested logs.
2. End coat the logs with a wax-type coating to prevent log end stain.
Stacking & Handling
3. After sawing, in warm weather, stack the lumber within 12 hours.
4. Use stickers between 8% to 10% MC; check the MC with a moisture meter; get the stickers directly from the unstacker rather than from storage.
5. Use stickers no more than 1-1/4 inches wide, by 3/4 or 7/8 inches thick.
6. Use a grooved sticker for a little extra advantage. This sticker allows some air movement under the sticker and thereby encourages the wood under the sticker to dry faster.
7. After stacking, the lumber must be kept out of the rain, especially at high MCs and in warm weather.
8. After stacking, if not loaded directly into the kiln, place the lumber in fast drying locations. Fan-sheds (or blow boxes) would be ideal; air drying is poor.
Predryer & Kiln Equipment and procedures
9. Brush snow off the lumber before entering the dryer.
10. Use a kiln load narrower than 16 feet.
11. Use a velocity over 500 fpm.
12. Do not use a "snow melting" or "thawing" kiln procedure.
13. Develop kiln relative humidities, within the first 6 hours of drying, that are at least equivalent to a 10 F depression. Larger depressions may be required, if recommended in the schedule. In humid weather, kiln temperatures may have to be raised slightly to achieve the low humidities required.
14. Load the kiln with only two rows of lumber rather than 3 or 4 for the first 12 to 36 hours to help achieve the required humidity immediately. Then, after the RH has been maintained for 12 or more hours, load the remaining lumber; the required RH should be more easily achieved in this manner at all times.
15. Use low kiln temperatures (110 or 120 F initially), as recommended in the schedule; never exceed 160 F, except during equalizing and conditioning.
16. Reverse fans every two hours.
17. Use correct kiln sampling procedures.
18. Do not over-condition the lumber.
19. If lumber has been air-dried or possibly mishandled, use a special kiln schedule that operates at very low temperatures.
20. After the first 10% to 20% MC loss, unstack and restack, using dry stickers in new locations.
Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison
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KnowledgeBase: Primary Processing: Air Drying Lumber
KnowledgeBase: Primary Processing: Kiln Operation
KnowledgeBase: Wood Engineering: Wood Properties
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