Q. I have been having a slight problem with my oak when I finish it. It is like the oak has a little bit of fuzz on it and so the fibers are popping up through the finish and I have to sand between coats very carefully to get the surface smooth again. Can you explain this?
A. Sometimes when the tree is growing, it produces a special type of fiber that is quite weak. As these fibers seem more common when the tree is under stress (wind, crooked stem, large branches, etc.), the fiber is called a reaction wood or tension-wood fiber. This fiber can have high amounts of cellulose, which absorbs stain, glue and finishes very easily. This fiber also can be low density and will have low strength. When the fibers, which are scattered throughout the lumber, are machined by dull knives or dull sandpaper, the fibers will tend to be pushed over rather than cut off cleanly. When you put a finish on such wood, the fibers will pop up through the finish, especially water-based finishes.
Unfortunately, it is nearly impossible to detect tension wood ahead of time. So, your first practical option is to use sharp tools (HSS is better than carbide in this case) and fresh sandpaper. If the problem still persists, then you can use a sanding sealer or glue sizing just before final sanding to stiffen the fibers so that they will sand off cleanly.
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