penetrating finishes such as solvent-borne oil-based semi-
transparent stains last longer on saw-textured wood than on
smooth-planed wood, many film-forming finishes such as
opaque stains and paints also last longer on saw-textured
wood than on smooth-planed wood. Finishes adhere better,
film buildup is thicker, and service life of the finish is longer
on saw-textured surfaces than smooth-planed surfaces, par-
ticularly for flat-grain lumber.
Plywood
As with lumber, species, grain orientation, and surface tex-
ture affect finishing of plywood. Manufacturers of softwood
plywood use a lathe to peel logs to give flat-grain veneer.
Peeling causes small checks parallel to grain. When the
face veneer is laid up to form the plywood panel, the side
of the veneer having lathe checks is placed interior to give
a surface free of checks. However, after plywood is placed
outdoors, wet–dry cycles (swelling and shrinking) cause
the checks to propagate to the surface (face checking). Face
checking sometimes extends through paint coatings to
detract from the appearance and durability of the paint
(Fig. 16–9).
Veneer produced by peeling gives flat-grain plywood and
it is commonly available with a saw-textured, abrasively
planed (smooth), or paper overlay surface. Douglas-fir and
southern yellow pine are available saw-textured (Table
16–1). Saw-textured plywood holds paint much better than
does smooth plywood. If smooth plywood is to be painted,
scuff-sand it with 50-grit sandpaper and use high-quality
latex paint. Latex primer and top-coat generally perform
better than oil-alkyd paint. Paint performs poorly on smooth
plywood if used as siding but reasonably well on smooth
plywood in protected areas such as soffits. Resin-treated
paper bonded to plywood forms a medium-density overlay
(MDO); MDO eliminates cracks caused by lathe checking
and provides plywood with excellent paintability, but the
edges are still vulnerable to water. Seal the edges with oil-
alkyd primer or an edge sealer formulated for this use. Paper
over-laid products should not be finished with semitrans-
parent stain or other penetrating finishes. Use film-forming
finishes such as paints or solid-color stains and ensure suf-
ficient film thickness (0.004–0.005 in. (0.10–0.13 mm), or
4–5 mils).
APA–The Engineered Wood Association (Tacoma, Washing-
ton) provides information on plywood grades and standards
(see Chap. 11).
Fingerjointed Lumber
To obtain “knot free” lumber, mills produce lumber that
consists of many small pieces of wood edge-glued and fin-
gerjointed at the end-grain (see Chaps. 10 and 12). Although
fingerjointed lumber contains no knots or other obvious de-
fects, most mills do not sort wood pieces prior to gluing to
give lumber with similar grain orientation and heartwood–
sapwood content. A particular board may contain pieces
from different trees, and each piece may have different
finishing characteristics; therefore, finishing requirements
are determined by the most difficult-to-paint component in a
fingerjointed board. Fingerjointed lumber is commonly used
for fascia boards, interior and exterior trim, siding, win-
dows, and doors. Paint often fails in a “patchwork” manner
according to the paintability of various pieces. The board
pictured in Figure 16–10 shows extractive bleed on the com-
ponent to the right, but not on the component to the left.
Some manufacturers decrease variability in fingerjointed
lumber. For example, fingerjointed redwood siding is avail-
able in clear all-heart vertical grain and clear flat grain.
Finishing fingerjointed lumber requires care to ensure con-
sistent finish performance on the whole board. To hide colorChapter 16 Finishing of Wood
Figure 16–9. Early paint failure on plywood caused by
penetration of moisture into surface face-checks.Figure 16–10. Differences in stain from extractives on
fingerjointed wood from the white pine group (either
eastern or western species) painted with acrylic solid-
color stain.