Chapter 16 Finishing of Wood
(temperate species), the cells have large open centers (lu-
mens) and thin cell walls. This is earlywood (also called
springwood). As the growing season progresses, cell walls
become thicker, forming latewood (also called summer-
wood). The combination of EW–LW (and vessels in hard-
woods) gives annual growth rings. The properties of these
growth rings affect the ease with which finishes can be ap-
plied (paintability) and how long finishes last (service life).
Cross-section micrographs of three softwoods and hard-
woods (Fig. 16–4) show three types of growth character-
istics. Softwoods may show “no transition” (no EW–LW
boundary, Fig. 16–4a), gradual transition (Fig. 16–4b), or
abrupt transition (Fig. 16–4c). Note: the “no transition”
softwood is a tropical species (that is, no seasons, therefore
no EW–LW transition). Hardwoods may be diffuse porous
(Fig. 16–4d), semi-ring porous (Fig. 16–4e), or ring porous
(Fig. 16–4f). As a first approximation for explaining finish-
ing characteristics of wood, the various wood species can be
grouped into three categories:
• Easy to finish (“no transition” or gradual-transition soft-
woods and diffuse-porous hardwoods)
• Moderately easy to finish (abrupt-transition softwoods
having narrow LW bands and semi-ring-porous
hardwoods)
• Difficult to finish (abrupt-transition softwoods having
wide LW bands and ring-porous hardwoods)
The important message from wood anatomy is to look at
the wood. The six micrographs showing end-grain wood-
cell structure do not include all possible combinations of
growth rate, grain, and surface texture. When determining
paintability, look at grain angles. Look at the width of the
LW bands and the transition between them (Fig. 16–5). The
blocks show radial and tangential surfaces (that is, vertical-
and flat-grain surfaces for six softwoods and quarter-sawn
and flat-sawn for two hardwoods). Note the abrupt transi-
tions on the southern yellow pine and Douglas-fir and the
gradual transitions on the western redcedar and white pine.
Also, note the growth rate and width of the LW bands. Sur-
faces having abrupt transition, rapid growth rate, and wide
LW bands are difficult to finish, particularly on flat-grain
wood. Moisture-induced dimensional change increases as
wood density increases. Changes are greater for LW than
EW. Different dimensional change for abrupt-transition (or
ring-porous) species at the EW–LW boundary places stress
on coatings.
Shrinkage values given in Table 16–1 were obtained from
drying wood from its green state (fiber saturation) to oven-
dry (0% MC); swelling rates would be approximately the
same. Some species have wide bands of EW and LW. These
distinct bands often lead to early paint failure. Wide, promi-
nent bands of LW are characteristic of the southern yellow
pines, radiata pine, and Douglas-fir (Fig. 16–5a,b,c), and
getting good paint performance is more difficult on these
species. In contrast, white pine, redwood, and western
redcedar (Fig. 16–5d,e,f) do not have wide LW bands, and
these species give excellent paint performance. Diffuse-
porous hardwoods such as aspen (Fig. 16–5g) have a fine
surface texture and are easy to finish, whereas red oak
(Fig. 16–5h) has a highly textured surface and requires
surface preparation prior to finishing.Figure 16–3. Micrograph of red maple showing diffuse-
porous vessels. (Micrographs prepared by H.A. Core,
W.A. Côté, and A.C. Day. Copyright by N.C. Brown
Center for Ultrastructure Studies, College of Environ-
mental Science and Forestry, State University of New
York, Syracuse, New York. Used with permission.)Figure 16–4. Cross-section micrographs of (A) a tropi-
cal softwood (Podocarpus imbricate), (B) white spruce
(Picea glauca), (C) Douglas-fir, Pseudotsuga menziesii
(D) sugar maple (Acer saccharum), (E) persimmon
(Diospyros virginiana), and (F) white ash (Fraxinus
americana). The arrows show a single growth year for
the temperate species.