differences of the various pieces, use opaque finishes rather
than natural finishes (such as semitransparent stain). As with
other wood products, planed surfaces should be scuff-sand-
ed with 50-grit sandpaper prior to priming. Saw-textured
lumber should hold paint better than planed lumber.
Particleboard and Similar Reconstituted Wood
Products
Reconstituted wood products are made by forming small
pieces of wood into large sheets; sheets are cut into 1.2- by
2.4-m (4- by 8-ft) panel products or other sizes such as sid-
ing. These products are classified as particleboard or fiber-
board, depending upon the nature of the wood component
(see Chap. 11).
Particleboard is made from splinters, chips, flakes, strands,
or shavings. Flakeboard is a type of particleboard made
from large flakes or shavings. Oriented strandboard (OSB)
is a refinement of flakeboard; the flakes have a large length-
to-width aspect ratio and are laid down in three layers, with
the flakes in each layer oriented 90° to each other as are
veneers in plywood (see Chap. 11). Most OSB is used inside
the external envelope of structures for sheathing and under-
layment, however it contains “exterior” adhesives and water
repellent. The water repellent gives OSB water resistance
while in transit and storage prior to construction. The water
repellent does not decrease paint adhesion.
Lumber characteristics, such as grain orientation, specific
gravity, grain boundary transition, warping, and splitting,
are not considerations with particleboard, but paint applied
directly to particleboard performs poorly. Differential di-
mensional change of surface flakes causes telegraphing, and
paint usually cracks and peels (Fig. 16–11). Telegraphing is
the formation of an uneven paint surface caused by swelling
of flakes and particles under the paint. Telegraphing occurs
on all types of particleboard, but not on fiberboard. Adhe-
sive failure leads to loss of flakes from the surface. Figure
16–11 shows painted flakeboard after 3 years outdoors. The
area on the left has one coat of acrylic-latex top-coat and
the area on the right has one coat of oil-alkyd primer and
acrylic-latex top-coat. The single coat (top-coat only) has
failed, and the area having two-coats (primer and top-coat)
is starting to fail, particularly over large flakes. Products
intended for outdoor use, such as siding, are overlaid with
MDO or wood veneer to improve paint performance. Prod-
ucts having MDO can be finished in the same way as other
paper-overlaid products. Seal edges with a product specifi-
cally formulated for this use, and apply an oil-alkyd primer
to give additional water resistance (see Plywood).
When finishing particleboard that does not have a paper
overlay, use a three-coat latex paint system on the surface
and seal edges as described above. However, do not expect
long-term paint performance.
When particleboard or OSB, without an overlay, is used
outdoors, it requires a rigorous maintenance schedule (often
every 6 to 12 months).
Mechanical pulping produces wood fibers that are dry- or
wet-formed into fiberboard (Chap. 11). Hardboard is a dense
fiberboard often used for exterior siding. Hardboard is avail-
able in 152- to 203-mm (6- to 8-in.) widths as a substitute
for solid-wood beveled siding. The surface of fiberboard ac-
cepts and holds paint well, and MDO improves paintability.
As with particleboard, seal edges with oil-alkyd primer or
other suitable sealer.
Wood–Plastic Composites
Wood-plastic composites (WPCs) account for approxi-
mately one-fourth of wood decking. Manufacturers combine
wood flour, fibers, particles, or a combination, with poly-
ethylene, polyvinyl chloride, or polypropylene and extrude
“boards” in various profiles. Wood content and particle size
in the boards vary and thus their ability to accept a finish
varies. Boards high in wood content with large particle size
may accept a finish; boards high in plastic content may not.
Finish a small area to ensure the finish will wet the surface.
After the finish cures, check adhesion using the tape pull-off
test (see Chalking). Plastics are routinely finished in indus-
trial applications, such as car parts, by activating the plastic
surface using flame or plasma. This technology is not used
on WPCs for the construction industry, because most manu-
facturers do not expect their products to be finished.
Treated Wood
Wood used in structures fully exposed to the weather, such
as in decks and fences (particularly those portions of the
structure in ground contact), needs preservative treatment to
protect it from decay (rot) and termites. Wood used in ma-
rine exposure also requires preservative treatment to protect
it from decay and marine borers. For some uses, building
codes may require treatment of wood with either preserva-
tive or fire-retardant, or both.
Wood is pressure-impregnated with three types of preserva-
tives: (a) preservative oils (such as coal-tar creosote), (b)
organic solvent solution (such as pentachlorophenol), andGeneral Technical Report FPL–GTR– 190Figure 16–11. Absorption of water causes differential
dimensional change of surface flakes to give an un-
even surface (telegraphing).