On Lumber Defects

When we were kids a “bow” was something our sister wore in her hair. A “crook” robbed banks. The “twist” was a dance. A “check” was used in lieu of cash. And a “shake” was a cold drink made from ice cream that made us fat.

Now, as contractors (and woodworkers) we have had to learn a new meaning for each of these words. Each one describes a lumber defect. Whether it’s a deck, dock or gazebo, a room addition or a remodel, it makes sense to know how to properly identify defects in lumber. Knowing what to look for may help to prevent you from paying premium prices for junk material.

Most lumber is sold green as opposed to dried. Green lumber contains the natural moisture and resins found in every tree. As it air-dries a small percentage of green lumber has a tendency to change shape. It bends, curls and splits. Not a good thing if you want to build something straight. To prevent such damage lumber is dried in an oven to remove natural moisture under controlled conditions. Unfortunately, the drying process is expensive.

Where many lumber stores will discard badly damaged wood others make a living selling dregs to unwary consumers. Some defects are simply aesthetic and others are structural. The following will give you an idea of what to look out for:

Lumber that has a bow in it doesn’t get its name from that thing made of ribbon in a little girl’s hair. In fact, bowed lumber is curved much like the archery devise of the same name. Stood on end a bowed board looks like an archer’s bow. Eyeing the board from its narrow edge, the center is on one plane and both ends are on another. Bowed lumber is not structurally unsound. However, it should only be used where nailing will cause it to be straightened out. Decking boards that are bowed can be nailed straight and flat. A board that appears bow-shaped when viewed from the wide surface is described as being “crowned”. If a crowned board is laid on a flat, horizontal surface where the ends touch and the center is raised the board has been laid crown up. With the center touching and the ends in the air the board would be considered laying crown down. When building floor joist carpenters are taught to lay crowned boards “crown up” for maximum strength. Moderately crowned lumber is structurally sound and can be easily straightened when used for decking.

Wood that has a cup in it is not meant to be used to hold coffee. Cupped wood is just another curved piece of lumber. As viewed from an end, cupped wood is slightly “C” or “U” shaped. Cupped wood cannot normally be straightened with nails like bowed and crowned pieces. Although it is structurally sound, if it continues to cup after being nailed in place it can literally pull the nails out as it changes shape. Attempting to flatten a cupped piece of wood by trying to nail it flat usually results in a full-length split of the cupped board.

No, it’s not a dance. Twisted wood results when spiraling fibers become dry. Sighting down the length of a twisted board reveals a timber that is similar in appearance to a barber pole. There is only one place for twisted wood – the kindling pile.

Nope, this is definitely not an account where money is kept. You might think of checking as lumber’s stretch marks. With lumber these are stretch marks that can be a serious problem. When exterior fibers dry more quickly than interior fibers small fractures, splits and cracks appear on the surface of the board that look like spider webbing or a series of stretch marks. Checked ends mean reduced lumber strength. It is not a good idea to use such material for framing. Checking along the length of a board does not indicate a loss in strength. However, wood that has checking along its length would not be good for decking.

We like chocolate or vanilla. Just kidding. A shake in wood is where the end-grains have separated. This is bad since it must be assumed that the separation travels the length of the board – even if it can’t be viewed from the other end. This type of lumber should not be used for rafters, joist or beams since wood with shaked fibers is weak.

Wane’s World was one of our favorite movies. Actually, wane in lumber is the presence of bark or a lack of wood at the edges. With waned wood the problem has nothing to do with the lumber itself and everything to do with a sloppy sawyer at the lumber mill. To err is human – right – unless someone wants you to pay for the sawyer’s mistake. In that case we suggest you ask for a discount. The wood is probably OK structurally, but isn’t as large as the size you paid for.

This is what you may wish to call the person who charges you full price for wood that contains any of the above defects. A crook is also another term for lumber that is crowned. We have often wanted to crown the crooks that prey on unwary consumers by selling defective lumber.

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