Drying Oak Lumber: Step 1, Assessing the Raw Material

      The first step in drying Oak is to know the characteristics of the lumber you're planning to dry. July 29, 2012

From Professor Gene Wengert, forum technical advisor:
The first step in drying oak lumber is to determine what wood you have. The four different oak drying groups are red upland, white upland, red lowland and white lowland. As a general rule, lowland means that the rings are spaced more than 1/4 apart.

Next, determine the quality of the wood. Look for signs that the wood has been previously dried, perhaps air dried. If someone else started the drying process, they may have surface checked the wood. You cannot heal these checks and may actually make them worse even with normal drying.

Also, look at the lumber to make sure there is no shake (a separation parallel to the rings rather than across the rings; potentially a foul odor as well). Virtually all shake indicates a bacterial infection in the wood and such wood is difficult or impossible to dry without checks, honeycomb, and so on.

Check the wood for excessive fuzzing from sawmilling. Fuzz indicates tension wood. Tension wood is very weak and also results in fuzzing when machining.

Check the grain pattern for any quartersawn grain. Quartersawn lumber requires about 15% longer drying time.

Check the grade, as lower grade lumber has more knots and grain deviations, which mean more warp and checking around the knots.

Be aware that circle sawn lumber has as much as 10 times more likelihood of checking compared to band sawn lumber.

Check the thickness. Non-uniform thickness can mean that thinner pieces will be able to cup more easily. Thicker lumber takes longer to dry; 10% thicker takes maybe 15% longer to dry.

End coating, which should be done when the lumber is first sawn for the best benefit, will prevent virtually all drying end checks. End checks can turn into honeycomb that can travel down the piece of lumber. A commercial end coating, properly applied, costs about $3 per MBF but the benefit is often over $30 per MBF.

Forum Responses
(Sawing and Drying Forum)
From contributor J:
Dr. Wengert, how can I tell if the lumber is dipped or not, and what exactly is the purpose?

From Professor Gene Wengert, forum technical advisor:
Dipping lumber refers to applying an insecticide and fungicide, and sometimes an iron stain inhibitor, to the lumber. The lumber is submerged in the solution, which is where the name "dipping" comes from. The dip chemicals penetrate into the green lumber perhaps 1/100" and thereby form a protective layer of poisoned wood on the outside, preventing new insects or fungi from getting into the wood. The primary reason is to control the blue stain (also called sap stain) fungus, which, when present, turns the sapwood grey or dark blue. There are test kits that you can buy to test for the presence of the fungicide.

Dipping is seldom done in the northern climates as the wood is cool enough that fungi are not exceptionally active. Southern oak may be dipped, but there is also an enzymatic grey stain (non-fungal) that gets into the sapwood if drying is not done immediately, so dipping is not a cure-all. Dipping can give one a false sense of security, so they delay stacking the lumber and some quality loss is therefore likely.

From contributor J:
So if I buy lumber from a sawmill, how can I haul it from his place to mine if he doesn't dip the lumber? And do the bolsters have to be dried as well before using them?

From Professor Gene Wengert, forum technical advisor:
You can buy undipped, freshly sawn lumber in cool weather, drive home promptly, and stack it right away. Then put the lumber in a good drying location.

From contributor A:
Dr. Wengert, why is circle sawn lumber 10x more likely to check than band sawn lumber as indicated in your post?

From Professor Gene Wengert, forum technical advisor:
In general, circle saws are not sharpened as sharp as band saws. That is, a circle saw can be run while it is quite dull, but band saws must be quite sharp or they will not run (break, come off, etc.). A dull saw tears the wood fibers much more than a sharp saw. These tears are essentially very small checks and as such are very easy to aggravate and worsen.

Step 1, Assessing the Raw Material
Step 2, Stacking
Step 3A, Measuring Moisture Content
Step 3B, Sample Boards

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