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For Maintenance Painting
New coatings technologies reduce downtime and application costs
By Dave Schutz
Product Information Specialist
The Sherwin-Williams Company
Choosing protective coatings for the wide range of structures and exposure conditions
in a plant can be a challenge for any specifier. Extreme humidity, harsh chemical
exposure, lighting and cleaning methods, for example, can vary
widely from one area to the next in any industrial plant.
But coatings specifiers can effectively manage the task by following this five-step system:
- Establish plant zones;
- Classify corrosive environments;
- Analyze all application considerations;
- Consider past performance of coating options, using case histories, comparative studies and test results as predictive tools
- Look closely at new coating technologies, such as waterborne, surface-tolerant, low-temperature and dryfall coatings.
Establish and map plant zones. Start with a
thorough analysis of the service conditions of all
coated structures. To make this task more manageable,
the facility and/or structures being protected
should be sectioned into zones. Create
maps that delineate zone boundaries and identify
each structure within a zone.
Classify corrosive environments. In general,
look to classify your corrosive environments into
the following simple categories: normal, light,
moderate or severe. To do so, start by identifying
the type of material to be coated, such as carbon
steel, galvanized metal, concrete, plastic or wood.
For steel substrates, visual inspection of the steel
surface using ASTM D610, Test Method for
Evaluating Degree of Rusting on Painted Steel
Surfaces, is useful.
Environmental variables that contribute to
corrosion include condensation, humidity, UV
light, wet/dry cycling, temperature cycling, abrasion,
immersion, and the presence of harsh chemicals
and solvents. These variables frequently have
a synergistic effect upon one another, multiplying
corrosion potential.
To assist specifiers in classifying corrosive environments
and choosing which protective coating
system to use in a particular plant area, the Steel
Structures Painting Council (SSPC) developed
its Environmental Zones Painting Systems,
which identifies 12 Environmental Zones, from
0 (interior exposure) to 3E (severe chemical exposure).
Along with a description of each zone, the
reader will find a recommended coating system
suitable for use in each area.
Analyze all application considerations.
Application considerations can have a significant
effect on coatings specification.
For example, will Food and Drug
Administration (FDA) regulations
affect coatings selections for the
zone in question? Can the surface
be properly prepared to accept the
recommended coating system, or,
if there are limits on surface preparation,
would an alternative system
provide better protection? Will production
continue while painting is in progress?
Will plant workers be present in adjacent areas?
Will plant safety be influenced? What physical
limitations may impede coating application?
To help plant specifiers evaluate all of these
variables, industrial painting contractors and coatings
manufacturers may be called upon to make
recommendations. Today there are many new
coatings that require less labor to apply, minimize
disruption to the plant and shorten downtime.
Consider case histories, comparative studies
and test results. Predicting how a particular
coating will perform under site-specific conditions
is extremely important. Case histories and
comparative studies aid in this process. Results
from accelerated laboratory exposure tests are also
useful, although not all accelerated tests provide
meaningful information. For example, the longstanding
salt-fog method (ASTM B 117) has
been found to be particularly poor at forecasting
coating performance. While no single exposure
test will duplicate actual atmospheric conditions
exactly, the newly adopted cyclic corrosion test
(ASTM D 5894) offers a much-improved technique
for comparing relative durability and service
life of protective coatings.
Look closely at new coatings technologies.
Low-odor, high flash points and easy cleanup are
among the characteristics that make waterbornes
attractive, downtime-reducing coatings options
for many specifiers. Thanks to new polymers, the
coatings are also chemical, abrasion and moisture-
resistant. They apply easily and can be
applied directly to bare steel or existing coatings.
For light to moderate industrial uses, acrylic
waterborne coatings are rapidly growing popular.
Noted for their excellent exterior color and gloss
retention, acrylic resins are transparent, yet provide
excellent adhesion and hide qualities. Since
their main polymer chain is a carbon-to-carbon
single bond, they are relatively inert and not as
susceptible to chemical change as many other
linkages, making them highly durable.
Also for light to moderate industrial uses,
waterborne epoxies have overcome temperature,
humidity and performance-related drawbacks of
past products. Waterborne epoxies can be
applied in temperatures as
low as 40 degrees F and offer
corrosion, chemical, impact and abrasion
resistance comparable to solvent-based products.
New technologies have helped make waterborne
urethanes appropriate for
moderate to severe industrial
uses. Urethane technologies have resulted in
a coating that uses a conventional resin with
a water reducible polyol rather than an
emulsion technology. This creates a film that
is very flexible and dense, and provides
excellent color and gloss retention on exterior
surfaces.
SURFACE-TOLERANT COATINGS
The high cost of surface preparation and
the time required for paint removal particularly
for complete removal of lead-based paint
can contribute greatly to the cost of maintenance
painting, not to mention extended
downtime. Surface-tolerant coatings typically
high-solids epoxies or epoxy mastics
minimize the need for surface preparation
without compromising coating performance.
Penetrating surface-tolerant primers work
by penetrating existing rust to create a
tight surface prior to subsequent coats.
These coatings may be applied over white
rusted and weathered zinc rich coatings, and
can be used as high-performance
primer/sealers for masonry surfaces.
Penetrating surface-tolerant primers are generally
applied at 2-3 mils dft.
Surface-tolerant primers are sound choices
in manufacturing environments where the
presence of blast particles in the air can damage
sensitive equipment, thereby eliminating
a conventional means of surface preparation.
After hand-tool or power-tool cleaning to
SSPC SP-2 and 3, the primer is generally followed
by a high-performance topcoat.
LOW-TEMPERATURE AND MOISTURE-CURED COATINGS
When maintenance painting during
cold weather is unavoidable, moisturecured
urethanes, cold-cured modified
epoxies and mastics and inorganic zinc
primers are able to cure efficiently and
form strong bonds to substrates.
Moisture-cured urethane systems are, in
fact, one of the more versatile coating systems
available for steel substrates. The systems
are surface tolerant, quick drying and
applicator friendly.
Although generally higher priced than
most industrial coatings, moisture-cured urethanes
are capturing a growing share of new
construction projects, particularly when longterm
performance and superior color and
gloss retention are required.
Power-tool cleaning is often the only
means of surface preparation required for
these types of urethanes.
DRYFALL COATINGS
Dryfall coatings were developed to be
spray-applied, with any overspray drying to a
powdery substance before the spray reaches
the ground. The paint droplet is transformed
to dust within eight to ten feet at 77 degrees
F and 50 percent relative humidity.
Because the resulting dust can be easily
swept away, job site cleanup can be fast, easy
and labor-saving.
Typically specified for use on ceilings
and walls of commercial and institutional
buildings, the most advanced dryfall coatings
are formulated not only to minimize
the labor involved in job-site cleanup, but
also to reduce the labor associated with
coatings application.
There are two types of dryfalls available
standard-grade dryfalls, which provide
two-coat coverage, and the new, premiumgrade
dryfalls, which require only half the
amount of material to achieve the same hiding
as their older counterparts. With just one
pass of a spray gun, sufficient opacity can be
achieved, even on new substrates, due to the
high pigment content of these coatings. In
addition, the newer dryfall formulations offer
excellent hiding even when wet, further eliminating
the temptation to apply several
unnecessary coats of paint.
Dryfall coatings can be applied to steel,
galvanized steel, aluminum, concrete, drywall,
wood and previously painted surfaces.
Surface preparation and recommended
primer should be performed as specified by
the manufacturer.
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