CHAPTER 16
Finishing of Wood
R. Sam Williams, Supervisory Research Chemist (Retired)
Contents
Factors Affecting Finish Performance 16–2
Wood Surface Properties 16–2
Wood Products 16–8
Weathering 16–11
Decay and Insects 16–13
Control of Water and Water Vapor 16–13
Compliance of VOC Finishes with Pollution
Regulations 16–15
Exterior Wood Finishes 16–16
Weathered Wood as Natural Finish 16–16
Penetrating Wood Finishes 16–16
Film-Forming Finishes 16–21
Application of Finishes, Special Uses 16–24
Porches, Decks, Deck Railings, and Fences 16–24
Treated Wood 16–24
Marine Uses 16–24
Boats 16–25
Panel Products 16–25
Fire-Retardant Coatings 16–25
Back-Priming 16–25
Factory Finishing 16–25
Finish Failure or Discoloration 16–25
Paint Cracking (parallel to grain) 16–26
Peeling and Flaking 16–26
Cross-Grain Cracking 16–26
Water Blisters 16–26
Mill Glaze 16–26
Intercoat Peeling 16–27
Chalking 16–28
Mildew 16–28
Loss of Gloss and Fading 16–29
Water Soluble Extractives 16–29
Blue Stain 16–30
Iron Stain 16–30
Knots 16–31
Pitch 16–31
Finishing Interior Wood 16–32
Type of Finish and Wood Fillers 16–32
Finishes for Wood Floors 16–33
Finishes for Items Used for Food 16–34
Wood Cleaners and Brighteners 16–34
Paint Strippers 16–35
Mechanical Methods 16–35
Chemical Methods 16–36
Lead-Based Paint 16–36
Literature Cited 16–37
Additional References 16–37Wood finishes (paint, varnish, and stain, for example) give
a desired appearance, protect wood surfaces, and provide
a cleanable surface. Many people consider appearance
most important when choosing finishes for wood (lumber
and wood composites). However, from a technical aspect,
protection is most important for wood used outdoors, and
providing a cleanable surface is most important for wood
used indoors. When selecting a finish, one should consider
appearance, protection, and cleanability and also how bulk
and surface properties of wood affect finish application and
performance (how long a finish lasts—its service life).
Wood properties such as density (specific gravity), growth
rate, heartwood–sapwood, earlywood–latewood, grain
angle, vessels, and texture vary within and across wood spe-
cies. Wood composites, such as plywood, fiberboard, and
oriented strandboard (OSB), have different properties. Of
the 18,000 to 25,000 known wood species (exact number
varies depending on the grouping of species), approximately
50 are commercial species used in the United States and
Canada. Chapters 2–4 give their properties. Of these com-
mercial species, researchers report finishing characteristics
for only a few species common to North America, Europe,
Japan, and the tropics. However, if one understands how
wood properties, finish, and environmental conditions inter-
act, it should be possible to estimate finish performance for
most wood species.
Performance depends on choosing an appropriate finish for
wood, considering the use conditions, and applying finishes
correctly in sufficient amount. For long service life, choose
wood products and finishes appropriate for environments
where they are used. Indoor use places less stress on finishes
than outdoor use. A climate having severe seasonal changes
(U.S. Upper Midwest, for example) places greater stress on
finishes then does a mild climate (such as the Pacific North-
west).
Guidelines in this chapter explain how to obtain long service
life for contemporary finishes on lumber and wood com-
posites used in the United States and Canada. The chapter
begins with a review of wood properties important for wood
finishing and describes effects of water and weathering on
wood and finishes. This background establishes a basis for
describing finishes for wood, their application, and common
types of finish failures (and ways to avoid them). Publica-
tions listed at the end of this chapter provide additional
information.