woodworkingnetwork.com | June 2019 | 38 |
by Robert Cox Jr. FINISHING
Quality control in industrial finishing
Focus on the substrate up rather than the topcoat down to get the best finishing results.
The quality plan for the development of the finish must focus on the finish from the substrate up, rather
than from the topcoat down. The quality requirements for a wood finish start
at the white room and encompass all
processes up to and including packaging
White room wood prep
The moisture content of the wood coming from the white room must be consistent. This allows the wood substrate
and the finish to “breathe” together. The
sanding operations in the white room
require attention to detail. The sanding
procedures for preparing the wood for
finish are primarily dictated by the porosity of the wood pieces. A soft, porous
wood, such as pine, requires aggressive
sanding and coarser paper grit.
Overly aggressive sanding (
burnishing the wood) on harder woods such
as oak, cherry, maple, birch and alder
prohibits proper finish adhesion. The
wood finish may flake off in its entirety
on woods with little pore definition.
This phenomenon is like a finish being applied to a piece of glass. The wood
finish will still “knit together,” called
“cohesion,” but it will not adhere to the
substrate. When manufacturers use aggressive sanding procedures on harder
wood, we recommended a fine mist of
water or alcohol to open up the wood to
better accept the finish, and the wood
finish adhesion will be improved.
Sandpaper and sanding processes
have a major impact on the quality and
look of the wood finish. Using too fine
sandpaper in final sanding prior to
finishing will cause colors to be lighter
in comparison to the standard. Worn out
sandpaper and/or varying grits of sandpaper change the color absorption of the
wood, and cause adhesion issues.
Dark colors are especially susceptible
to sanding and adhesion problems, and
the overall integrity of the wood finish.
Whites are also susceptible to adhesion
problems as high concentration/volume
of pigments (high PVC) are often used
to obtain the look wanted. If the pig-
ment concentration is too high and goes
above the CPVC (Critical Pigment Vol-
ume Concentration – the point at which
there is just sufficient binder to cover
the pigment surface as well as all the
particles in a close-packed system), adhe-
sion becomes an issue or in more simple
terms: basically too much pigment causes
Proper maintenance of equipment for
finish consistency cannot be overemphasized. The spray equipment must be
Consistent and effective finishing in a manufacturing setting requires proper execution of a
variety of variables from the substrate up.
Proper maintenance of equipment is
necessary for finish consistency, along with
testing of finish performance.