Characteristics of incoming lumber

Q. We buy a lot of lumber and have been getting more concerned about what characteristics we should be aware of and should inspect for.

A. The characteristics of the incoming lumber affect yield,processing costs, and ultimate performance of the cabinets, furniture and otherwood products that are manufactured. Many of these characteristics are not wellcovered in the standard grading rules, so only monitoring lumber grade andfootage will be inadequate.


By far, the most important characteristics are

            a. lumber gradeand footage,

            b. moisturecontent (average MC, MC variation from piece to piece and core MC).

It is prudent to have a rigorous program to evaluate these twoitems.


Further, other important characteristics to evaluate, listed inorder of importance (roughly; each plant is slightly different), are

            c. The presenceof shake (which indicates bacterially infected lumber)

            d. The lack ofend coating

            e. The presenceof large (over ¼-inch wide) end splits

            f. The presenceis side bend warp or twist warp

            g. The presenceof cupping warp

            h. The lumberwidth, especially if narrow

            i. The lumberlength

            j. The presenceof checks and honeycomb in oak

            k. The color,including the presence of gray or pink discoloration in ash and maple

            l. The presenceof drying stresses (also called casehardening)

            m. The presenceof the correct grain


Discussion of characteristics

a. Lumber grade and footage greatly affect the yield (orvolume) of parts, the quality of parts and time to process the lumber intoparts. You should receive the full range of quality allowed within a grade;that is, another lumber customer should not have received the best qualitywithin the grade and you received the lower quality.


My experience also shows that footage measurements are oftenincorrect; usually the actual footage is lower than the value on the invoice.


You will find that some suppliers are perfect, and these wouldnot have to be double checked.


b. Moisture content of the lumber must be at the correctlevel. If much drier than 6.0 percent MC, the wood will behave in a brittlemanner when machining, and will absorb glue rapidly potentially leading to a poorglue joint in panels. If the lumber is much above 7.5 percent MC (perhaps above8.0 percent MC, but I suggest 7.5 percent MC is better), the wood will shrinkin processing (poor glue joints, un-smooth surfaces and joints), andpotentially in use (delayed shrinkage with numerous potential problems).


The average MC must be correct, plus the variation of piecesaround this average must be small. Of critical importance when measuring the MCis the core MC. As you are aware, it is the core that ends up in the product,not the shell (or much of the shell). Further, the core MC does not change atroom temperature very quickly, so core values on finished goods indicate the MCat the time the wood left the kiln, even if it was not handled in the bestmanner during shipment or storage.


c. The presence of shake, which is a separation that runsparallel (not across) the growth rings, indicates bacterially infected lumber. Usuallythe infection is only a foot or two up the lumber. The risk is honeycomb whendrying, wet lumber, even though the rest of the piece is dry, and a foul odorthat can persist in the final product especially in humid conditions (such asin a bathroom or near a kitchen sink). Such wood should not be used; chop offthe end of the lumber before ripping.


d. The lack of end coating means that potentially 2”or more from the end or every piece of lumber will have to be trimmedoff. (The risk is greatest with the denser species.) Further, as end checks aredifficult to see as they move up the piece, it is possible that an end checkmight accidentally be included in a stave, leading to a small crack int hefinal product. With properly applied (mainly, put on thick enough) end coating,the trimming rehired will be 1/4 inches in most cases. For 8’lumber, this is loss of 4 percent with no coating and 1/2 percent withcoating; this 3-1/2 percent gain is worth about $25 per MBF or so, but the costof applying the coating at the sawmill is only $4 per MBF.


e. The presence of large (over 1/4-inchwide) end splits indicates that there is stress in the tree that isalso in the lumber and that will be in the components manufactured. If thehumidity and moisture content of the wood products never changed, then thisstress would not be an issue. But with changes in moisture, there is a stronglikelihood that the wood will twist and warp lengthwise slightly. Further, whenwood with stresses is machined, even though the machines, such as a planer orbelt sander, are perfectly flat, the stress will cause immediate warp when machining…mostlybow or side bend.


f. The presence is side bend warp or twist warp in the rawlumber indicates the presence of stress, steep grain angles, and/or tensionwood. All these characteristics within the wood will cause a slight amount ofwarp—bow, twist and side bend—in the componentswhen machining and in the final product if and when the moisture changes.


g. The presence of cupping warp indicates that the wood iscut from near the center of the tree, which again means that some warp—bow,twist, cup and side bend can be expected if the moisture changes.


h. The lumber width, especially if narrow, increases thepiece count and also reduces the overall yield. Both of these characteristicsresult in higher processing costs. The major concern would be for a load orbundle with quite a few narrow pieces. I would think that somewhere around 6”would be the dividing line. Of course, a few narrow pieces in every loadwould be normal. As a comparison, you might rip two 5”pieces and compare that to ripping one 10”piece.


i. The lumber length is important, with longer lumberbeing less expensive to process.


j. The presence of checks and honeycomb in oak whenlooking at dry lumber indicates that the lumber was not dried properly and thatyields will be lowered substantially. Checked lumber should be withdrawn fromproduction and returned to the supplier for a full credit.


k. Any discoloration, including the presence of gray orpink discoloration in ash and maple, blue stain or sap stain, and sticker stainin most species, is preventable through proper handling and drying of thelumber. (So-called mineral stain, usually caused by an insect, occurs in thetree and is not controllable during sawing, or drying.) Oftentimes, suchstaining is not obvious from the rough lumber. When visible, the grade andprice should be 2B Common, at best; or the lumber can be returned. When somepieces are stained, it is likely that more stain will be seen as processingproceeds.


l. The presence of drying stresses (also called casehardening)will cause immediate warp when machining and will make flatness of panels anddoors difficult to achieve. Such stress can be easily removed in the dry kilnduring normal drying procedures. The presence of such stresses indicate poordrying and often highly variable final moisture contents, along with otherdrying defects.


m. The presence of the correct grain, includingquartersawn grain, absence of sapwood, and so on is important.


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About the author
Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 45 years. He is extension specialist emeritus at the University of Wisconsin-Madison.