RED BOOK | April 2019 | woodworkingnetwork.com/redbook |53
Wood finishing FAQs
Wood finishing is one of the last processes in the manufacture of furniture or cabinets, and the first thing seen on the retail floor. The finish emphasizes the mission of the piece
with respect to its look and feel. With that in mind, here are
The following are some of the inconsistencies that can relate to
improper product and or execution controls:
Bleed -through: Alcohol-based dye stains can react with cata-
lyzed sealers and topcoats causing a bleed-through that is readily
apparent in the finish - usually red or green.
Drying issues: The process must allow the finish to dry and
cure from the substrate up rather than from the topcoat down.
This quality check cannot be overstated. In addition to good air
make-up in the room, the air in the ovens must be kept clean or
the solvent vapors, can cause the finish to cure with a greenish-
yellowish cast, due to the high acidity of the atmosphere.
Improper cure also can create blisters, and bubbles in the fin-
Blushing of the finish: This occurs mostly in multiple-step
ish, leading to poor finish adhesion, and results in a rough feel
to the final piece. Improper topcoat formulation also can result
in a “wavy cold gravy” appearance from the solvents flashing off
and drying too quickly. The solution is to correct the solvent
blend and/or add more flow agents. If the topcoat cures topside
down rather than substrate up, this is another reason the wavy,
cold gravy appearance will also appear. Make-up air and oven
temperatures should be addressed for correction.
finish applications and is caused by moisture laden air, usually
from high humidity. This can cause a “white blush” appearance
from the stains and glazes “blushing up” through the topcoat.
Blushing can be corrected in many ways, including reducing the air flow through the spray guns, along with the use of a
slower solvent to allow the finish to dry from the bottom up, not
topcoat down, Again, keeping the finishing room dry without
excessive humidity is important to controlling this step.
Lifting of the finish: If the catalyzed sealer is not cured
properly in conjunction with the curing of the catalyzed topcoat,
lifting of the finish occurs. This lift gives the finish an alligator-skin-like appearance, requiring costly clean-up and re-finishing.
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SANDING & FINISHING
Troubleshooting advice and other tips for quality wood finishing.
By Robert Cox