Q. We have some cabinets made from pine and I wonder what is the chance of grain raising. We work in an with an average EMC of 7 to 9 percent. The cabinets are then finished with water base coating. My question is what will this do to the grain (creating raised grain). I know dimensions change but what is the probability of the grain raising?
A. First, we need to make sure that we have the same definition for grain raising. Some folks might call that appearance of wood fibers sticking up through a finish as grain raising. This would be most common with the hardwoods and not too common with the conifers like pine. I would call this fuzzing or grain fuzzing. I prefer to call grain raising the appearance of the annual growth rings through the finish. In other words a flat surface becomes bumpy and the bumps are related to the annual growth rings. This is usually seen only on pines and other softwoods that have very distinctive annual growth rings.
Raised grain is more likely when there is heavy pressure on the surface during machining, such as from feed rolls, dull knives, knives with too much land, and/or high stock removal per cut. Heavy sanding pressure can also make grain raising more likely. What happens is that the high pressure pushes some of the wood cells (the dense darker wood cells within a growth ring) down into the soft cells below the surface. After machining, the surface looks very flat. But, now when moisture is added, especially moisture from a water-base finish, the crushed cells will pop back to their original size, pushing upward and creating the uneven surface called grain raising. (Special note: I have seen a few cases where heavy pressure from hand sanders can compress wood cells that then later pop back up when moisture is added creating a bumpy surface.)
The cure is not eliminating moisture, but rather fine tuning planing and sanding to eliminate excessive pressure. Sometimes machines are set up based on machining or sanding dense hardwoods and then are not readjusted for the softer wood like pine. Note that heavy planing or machining followed by light sanding is not enough...the entire machining operation needs to have a light touch.
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