FUSION Issue 3-2026 DIGITAL - Flipbook - Page 27
Air supply: the variable most
often assumed
lands on the surface is not uniform, and the
finish reflects this in ways that can be difficult
to attribute to a specific cause
during troubleshooting.
Except it is not, quite.
and adhesion. In solvent-based systems,
oil contamination creates fisheye defects
that are both difficult to diagnose and
time-consuming to fix. Neither type of
contamination is visible at the gun. Both
are entirely preventable with appropriate
filtration and regular maintenance of that
filtration equipment.
Air quality matters as much as air pressure.
Contaminated air carrying moisture, oil
vapour, or particulate from the compressor
or supply line reaches the gun and ends
up in the coating. In waterborne systems,
moisture contamination affects flash times
Pressure consistency also deserves more
attention than it typically receives. A
compressor that cycles, building pressure,
cutting out, dropping back, introduces
variation into the air supply that manifests
as variation in atomisation. The coating that
Fluid viscosity: the
overlooked calibration step
Viscosity is not fixed. It changes with
temperature. The same material from the same
tin will behave differently on a cold Monday
morning in January and a warm afternoon in July,
and the adjustment required to work within the
optimal range is not the same on both days. At
temperature extremes, the viscosity difference
in a waterborne coating can be substantial
enough to require a materially different
application approach.
Many operators assess viscosity by feel, or
not at all. A viscosity cup costs very little
and takes under a minute to use. It converts
a subjective judgement into an objective
number and removes one significant source of
variation from the process. Thinning beyond the
manufacturer's specified limits to compensate
for conditions that should have been managed
differently reduces film build and, in protective
coatings, compromises the corrosion resistance
of the applied system.
In marine and aerospace environments, where
compliance with coating system specifications
matters for warranty and certification,
temperature deviations during application are
process deviations. Not administrative details.
sensitive systems. Managing humidity in the
booth requires monitoring, not assumption.
The compressed air supply feeding a spray
gun is frequently taken for granted. The
compressor runs, the pressure gauge shows a
number, the gun gets connected. Job done.
Every coating has an optimal viscosity range
for spray application, and that range exists for
a reason. Too thick, and the material does not
atomise properly; the droplets are too large, the
fan pattern is too heavy, and the finish shows
texture. Too thin, and the material runs, sags, or
loses the film build needed for protection.
The booth environment
The spray booth exists to control the
environment during application, and the
conditions inside it affect the outcome
in ways that are easy to overlook until
something goes wrong.
Temperature affects not just viscosity
but cure behaviour. Most coatings have
application temperature windows, and
working below them extends flash and cure
times in ways that affect how subsequent
coats behave and how the final film performs.
Gun maintenance as setup
A spray gun that has not been properly
cleaned and maintained is not starting
from a neutral position. It is starting from a
compromised one.
Dried material in the fluid passages, worn needle
tips, damaged air cap orifices: each affects
atomisation, pattern consistency, and fluid
Humidity is particularly significant for
waterborne coatings, which are increasingly
prevalent as the industry moves away from
solvent-heavy systems. The moisture content
of the air affects evaporation rate during
application and cure behaviour after it. High
humidity slows flash times; very high humidity
can cause blushing and adhesion issues in
delivery in ways that cannot be corrected by
adjusting the controls. A gun producing a split or
distorted pattern because of a partially blocked
air cap will not produce a good finish regardless
of how well the operator moves it. The fault is
not technique. The fault is maintenance.
Spray gun cleaning and inspection should
be systematic. The fluid tip and air cap are
At the gun itself, measuring inlet pressure
is not the same as measuring atomising
pressure. The pressure drop across the gun
body means the figure at the regulator and
the figure at the air cap are not identical, and
the difference varies with gun design, hose
diameter, and flow rate. Working from inlet
pressure alone leads operators to settings
that feel familiar but may not be delivering
the atomisation the coating actually requires.
Contamination control matters too.
Overspray accumulation on booth walls
builds over time and becomes an airborne
contamination source that affects finish
quality in ways that are easy to miss. Products
like the BAXT LayerLOCK multi-layer booth
wall protection system allow clean removal
of accumulated overspray layers without
downtime, a practical solution to what is, in
busy shops, a genuine and recurring problem.
wear items that need regular checking and
replacement when worn. Needle seals and
packings are another common source of
gradual deterioration. A gun performing well
six months ago may not be performing well
now, and without routine inspection, the
degradation is invisible until it appears as a
defect on a job that matters.
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