The Ghosts Of Stickers Past

Recently, I came across a problem I've never seen before. The problem was that there were very light lines about 1" wide, that ran across the width of my lumber. These lines occurred every th ree feet or so along the length of the lumber.

I tried to sand the lines out, but it got to the point where I would have been changing the thickness of the pieces if I'd continued. When I finally applied, the finish, the lines were more apparent than I had anticipated.

Do you knoiv what these lines are, or what causes them, and what can be done to prevent them?

Thomas Phipps Chicago, Illinois

To find out w:hat these lines were, we decided to talk to Jim Ward, technologist with the Forest Products Laboratory in Madison, Wisconsin.

According to Jim Ward, the lines run ning across the face of lumber are either sticker stains or sticker marks. Both conditions occur during the drying process, and are caused by the narrow pieces of lumber (stickers) that are used to separate the layers of boards as they dly.

Although stickers allow free air movement throughout the stack of lumber during air and kiln drying, they can also create some unique problems.

STICKER MARKS. Sticker marks appear as narrow bands (usually about 1" in width) across the face of a board that are lighter than the rest of the piece.

As lumber dries, it's normal for the exposed surface of the boards to darken slightly as it reacts with the oxygen in the air (oxidation).

Sticker marks occur when the contact between the sticker and the board is tight enough to prevent oxidation from occurring on the area where the sticker and the lumber meet. This causes the area covered by the sticker to appeal1 lighter than the rest of the board, simply because it hasn't darkened by oxidation.

sticker stains. Sticker stains are just w:hat their name implies — stains caused by the stickers. Unlike sticker marks, sticker stains can be any color that's darker than the surrounding wood.

Sticker stains can be the result of several different conditions. One condition is when moisture is trapped between the sticker and the board, creating a favorable environment for molds that stain the wood. This type of stain often penetrates deep into the board.

Sticker stains may also be caused by stickers that are wet or partially decayed, or by dark colored stickers whose color leaches into the board.

Most sticker stains and sticker marks are removed when rough lumber is planed. But there's often a "ghost" image that remains after the board is planed, and they're usually quite noticeable after a finish is applied.

The only way to eliminate the problem of sticker stains and sticker marks is to avoid them from the start. Carefully inspect each piece of surfaced lumber, and look for the faint bands that run across the width of the board.

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