What makes the lumber blue?
Blue stain is a common cause for the discoloration of lumber. Certain dark-colored microscopic fungi cause a bluish or grayish discoloration in the sapwood of the tree. However, not all blue stains are blue. Common stain shades can be blue to bluish black or gray to brown. Sometimes, the stain coloration in lumber may appear as red, yellow, orange, or purple.
Does it affect the strength properties?
Blue stain has no effect on the performance and strength of lumber. Structural lumber is not downgraded due to the presence of blue stain and should not be labeled inferior lumber.
Where can blue-stained lumber be used?
Because blue stain does not detract from the strength properties of dimension lumber, blue-stained lumber can be used for exactly the same purpose as non-stained lumber. Just be certain that the lumber has a grade mark accredited by the American Lumber Standards Committee (ALSC), which identifies the grade, moisture content, inspection service, species, and mill identification number.
What is it... blue stain or mold?
Blue stain is not mold. However, for a simple test to determine whether or not a piece of lumber is blue-stained or growing mold, lightly rub the affected surface of the wood. Mold grows on the surface and can be brushed off or smeared, where as blue stain penetrates deep into the wood and cannot be removed.
What about health and safety concerns?
Blue stain poses no health risk, and blue-stained lumber is safe to handle. The same safety rules for using non-stained lumber apply to blue-stained lumber:
- Wear eye protection and a dust mask when sawing or machining lumber.
- Avoid prolonged inhalation of sawdust.
- When the work is completed, wash areas of skin contact thoroughly before eating or drinking.
- Wash clothing that accumulates sawdust separately from other household clothing and before reuse.
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