Q: Our main red oak supplier sprays water on his logs during the summer. I have heard that some guys don't buy red oak if the logs were under water because you can't keep the sap from staining. Is this true?
A: The sap wood in oak, maple, poplar and most other species can stain for two reasons. First, if the wood dries a bit, then there is enough oxygen for a dark blue colored fungus to grow and stain the sapwood (the white outer portion of the log). This is called the blue stain or sap stain fungi. Second, the starches and sugars in the tree are stored in the sapwood. As soon as the tree is cut, these chemicals begin to oxidize and, similar to an apple that has a bite taken out of it, the oxidation results in a brown, pink or gray color within the wood. This oxidation requires warm temperatures.
The sprinkling of logs (with the equivalent of about 2 inches of rain daily) for several weeks prior to sawing into lumber can prevent fungal damage by preventing the wood from drying out. If there is no oxygen, the fungi cannot become active. Applying a fungicide to freshly sawn lumber can also prevent fungal damage after sawing. However, the oxidation reaction cannot be prevented in warm weather if the logs or lumber are stored for any length of time, even if sprinkled. The discoloration from this oxidation may not occur or be noticed for days or weeks later, but the damage is done much earlier. The oxidation grey stain, also called enzymatic stain, in logs during warm weather is controlled by rapidly processing the logs into lumber and the relatively fast drying of the freshly sawn lumber.
Within our industry, there are many people that do not buy green lumber in the warmer months unless they know that the logs are fresh and then the lumber can be shipped and stacked promptly for drying. Sawmills that have their own drying operations can often, if they move rapidly, handle logs and lumber in warmer months.
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