Factors Affecting Finish
Performance
Wood surface properties, type of wood product, and weather
affect finish performance.
Wood Surface Properties
Wood anatomy, manufacturing processes, moisture content
(MC), dimensional change, extractives, and changes as
wood ages determine wood surface properties.
Anatomy
Wood species (thus its anatomy) is the primary factor that
determines surface properties of wood—properties that af-
fect adhesion and performance of finishes. Wood anatomy
determines whether a wood species is a hardwood or soft-
wood, not the density (specific gravity) or its hardness.
Finish performance is affected by
• density (overall density, earlywood (EW)–latewood
(LW) density difference, and how abruptly density
changes at the EW–LW boundary),
• thickness of LW bands,
• ray cells (number and placement),
• vessels (size and location),
• extractives content, and
• growth rate (some species grow faster than others,
and environment affects growth rate within a specific
species).
Most wood cells (called tracheids in softwoods, fibers in
hardwoods) align parallel (axial) to the stem or branch.
Softwood tracheids support the tree and transport water
and nutrients. Hardwood fibers just support the tree; hard-
woods have special cells (vessels) for transporting water
and nutrients. Vessel cells are open at each end and stacked
to form “pipes.” Axial tracheids and fibers are hollow tubes
closed at each end. In softwoods, liquids move in the axial
direction by flowing from one tracheid to another through
openings called pits. Liquid transport between the bark and
center of the stem or branch in hardwoods and softwoods is
by ray cells. Figures 16–1 to 16–3 are micrographs show-
ing the orientation of axial and ray cells for white spruce,
red oak, and red maple, respectively. Note that the soft-
wood (Fig. 16–1) has no vessels. The large openings are
resin canal complexes (common to spruce, pine, larch, and
Douglas-fir). Figure 16–2 shows red oak, a ring-porous
hardwood. Large-diameter vessels in ring-porous species
form along with EW; later in the growing season, the ves-
sels have smaller diameters. Figure 16–3 shows red maple, a
diffuse-porous hardwood; small vessels having similar size
form throughout the EW and LW. Hardwoods can also be
semi-ring porous.
Axial and ray cells form in the cambium, a layer of cells just
under the bark. In the early part of the growing season
General Technical Report FPL–GTR– 190Figure 16–1. Micrograph of white spruce showing
gradual transition of cell wall thickness and resin canal
complexes. (Micrographs prepared by H.A. Core, W.A.
Côté, and A.C. Day. Copyright by N.C. Brown Center for
Ultrastructure Studies, College of Environmental Sci-
ence and Forestry, State University of New York, Syra-
cuse, New York. Used with permission.)Figure16–2. Micrograph of red oak showing ring-
porous vessels. (Micrographs prepared by H.A. Core,
W.A. Côté, and A.C. Day. Copyright by N.C. Brown Cen-
ter for Ultrastructure Studies, College of Environmental
Science and Forestry, State University of New York,
Syracuse, New York. Used with permission.)