Specifying and Selecting Coatings Presented by: Troy Fraebel,
Sherwin Williams
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Introduction This webinar will provide guidance on how to
properly specify and select a coating system for a specific
substrate (carbon steel, other metals, concrete, previously
coated), structure, and environment.
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Painting Project Specification A statement of particulars,
describing the dimensions, details, or peculiarities of any work to
be undertaken.. Legal document. Part of a contract. Provides the
(technical) rules. Practical document. Requires thorough planning.
What, where, when, but NOT so much on how!
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Painting Project Specification Contents Scope of work. Areas to
be coated and not coated. Site specific requirements. Paint
materials and suppliers. Surface preparation, application, and
inspection requirements using standard methods.
Specification Writing Techniques Use short sentences. One
requirement per sentence. Place action words at the beginning. Use
strong verbs. Never repeat descriptions or requirements. Define
words that may be misunderstood. Use the same writing style
throughout.
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Important Word Meanings Shall. Essential requirement. Should.
Preference or strong recommendation. May. Used when alternatives
are acceptable.
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Coating Specification Formats Construction Specification
Institute (CSI) SSPC modified CSI format Major Sections General
Products Execution
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Coating System Selection Coating mechanisms and types Type of
substrate (steel, concrete, etc.) Prevailing service environment
(immersion?) Level of surface preparation possible Access to the
work Owners desires and expectations: Intended service life of
structure Desired service life of coating Worker skills and
equipment availability Aesthetics (gloss & color retention)
Timing Economics
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Making Steel Corrode Anode Cathode Metallic Pathway
Electrolyte
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How Coatings Protect Surfaces Barrier Inhibitive Sacrificial
Corrosion Prevention Stop the deterioration of a substrate.
Corrosion is a natural process that displays the tendency of
materials to give up energy and return to its natural state.
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Zinc-Rich Primers Contain High Percentage of Zinc Dust in the
Dried Film So That There Is Direct Contact Between Zinc Particles
and Steel Sacrificial / Galvanic Protection (like galvanizing)
Corrosion Protection Prevention of Undercutting
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Solvent Based Epoxies Excellent Alkali, Solvent, and Water
Resistance Good Abrasion Resistance Good Acid Resistance Good
Exterior Durability but... Low Temperature Application Available
Typical Dry Heat Resistance to 250 F
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Solvent Based Alkyds Application as low as 40F Single Package /
Ease of Application Heat Resistance to 200-250 F Embrittle With Age
Prone to Yellow / Saponify Require modification for exterior
topcoats
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Waterborne Acrylics Single Component Water Based Fast dry and
fast re-coat Good color and gloss retention Primers must contain
inhibitors Low stress
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Polyurethanes / Polyureas / Polyaspartics Aliphatic Excellent
Color Retention Excellent Gloss Retention Primarily Used as Finish
Coats More Expensive than Aromatics Aromatic Yellows & Chalks
in Sunlight Yellows & Chalks in Bright Artificial Light Used as
Primers & Intermediate Coat Less Expensive than Aliphatics
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Moisture Cured Urethanes Can be surface tolerant Can be applied
during high humidity Easy to application Fast cure / fast recoat
Low temperature application to 20 F. Single component Reinforce
with micaceous iron oxide Aliphatic topcoats
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Types of Substrates Coated
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Types of Steel Cold-rolled Hot-rolled Stainless steel
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Cold-Rolled Steel Typically steel coils; typically thin sheet
steel. Produces a denser, smoother surface than hot-rolling.
Phosphating may be used to promote coating adhesion; otherwise
coatings may not bond well.
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Hot-Rolled Steel Typical of structural steel used in
construction. Manufacturing process creates a bonded layer of iron
oxide called mill scale. Smooth Cathodic Differential
expansion
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Stainless Steel Better mechanical properties and greater
resistance to corrosion than mild steel. Numerous grades of
stainless steel (add chromium and... ) Harder than mild steel Prone
to stress corrosion cracking (SCC)
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Hot Dip Galvanized Surfaces Application of a zinc coating to
steel by dipping it in molten zinc or by depositing zinc on the
steel through electrolytic means. Post-treated with oil or a
chromate conversion coating to protect from white rust, a
wet-storage stain. Post-treatments must be removed before coating.
Alkaline substrate. Oil-based alkyds may saponify.
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Aluminum May require chemical treatment, wash priming, and/or
brush off blasting with a soft abrasive. SSPC-SP 16
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Ductile Iron Use Standard NAPF 500-03 Applying steel surface
preparation specifications to ductile iron is inappropriate, and
may actually result in damage to the pipe surface with subsequent
reduced coating effectiveness and life expectancy.
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Concrete A composite material comprised of a Portland cement
and water mixture that serves as a binder for embedded particles of
coarse and fine aggregate.
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Concrete Characteristics Alkalinity (pH range of 9 to 12)
Porosity Moisture Movement of concrete (i.e., cracking)
Other Substrates Wood or plywood Polyvinyl Chloride (PVC)
Fiberglass Reinforced Plastic (FRP)
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Demands of Environments on Coating Systems
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Questions to Ask Is the coating being applied to an interior or
exterior space? What is the atmospheric service environment? Will
the coating be exposed to abrasion and impact? What is the surface
temperature once in service? Will there be a cleaning or cyclic
exposure?
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Questions to Ask Will the coating be immersed in chemicals?
Type Concentration pH Temperature Primary or secondary containment
What are the application conditions? Is the coating being applied
in a climate- controlled shop environment or in the field? What is
the surface temperature during application?
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Interior Service Environment Coatings Coatings need not
withstand sunny conditions. Maybe climate controlled.
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Exterior Service Environment Coatings Designed to withstand
sun, rain, and snow. Remain flexible after curing; wont crack or
peel as it expands and contracts with changes in temperature and
humidity. Additives enhance mildew-, fungus-, and
UV-resistance.
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Service Locations What are some different service locations?
How might location affect the type of coating you would select?
What factors should be considered?
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Inland, Rural Free from the corrosive influence of airborne
salt; polluted air and rain may still be present.
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Heavy Industrial High corrosion rates High atmospheric chemical
concentration (i.e., sulphur dioxide, nitrous oxide)
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Marine High concentration of salt mist (chlorides). Not always
in direct contact with salt spray or splashing waves. Often in
conjunction with heavy industrial environments.
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Immersion Better surface preparation. More impermeable.
Typically not UV stable. Must resist constant exposure to the
cargo.
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Alternating Immersion Any area in which immersion in water is
combined with period of exposure to the atmosphere just above it.
Steel in a tidal range. High waterline in a tank.
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Condensing Humidity Service Example: Headspace in a tank Indoor
pool with condensation on ceiling Cold pipes
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Chemical Environments Strong concentrations of highly corrosive
gases, fumes, and chemicals that come in direct contact with the
coated surface. Mild to severe; direct immersion or splash.
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Underground Buried surfaces in direct contact with soil.
Possibly highly acidic. Compatible with cathodic protection.
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Abrasion and Impact Coatings exposed to particle objects that
rub, scrape, impact, or erode the surface by friction (i.e.,
pipeline, dam gate).
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Final Service Temperature Certain coatings are prone to limited
chemical resistance and early failure when exposed to high
in-service temperatures.
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Other Factors to Consider What else might impact your choice of
coating selection beyond the service environment?
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Application Temperature Apply coating system only when the air
and substrate temperature are within the range indicated by the
manufacturers written instructions on the product data sheet
(PDS).
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Coatings and Moisture Not applied to wet or damp surfaces
unless formulated by the manufacturer for this type of application.
Not applied on frosted or ice-coated surfaces. Typically not
applied when surface temperature is less than 5 o F (3 o C) above
the dew point.
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Previously Coated Substrates Generic Type Assessment of Current
Paint Percentage (%) of corrosion Adhesion to substrate and other
coats Thickness (DFT) Number of coats Chalking, blistering, etc.
Test Patch!
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Adhesion Test adhesion of existing coating to itself and to the
substrate. Low adhesion values can indicate possible delamination
during overcoating.
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Multiple Coating Layers High internal stress possible. Can
cause delamination and reduce intercoat adhesion when overcoated.
Delaminated and cracked coatings are not good candidates for
overcoating.
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Chalking and Erosion Typical of aging epoxy and alkyd
coatings.
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Coating Compatabilty Small field patch tests. Apply proposed
repair system to small deteriorated areas using same surface
treatment planned for repairs. Visual defects and adhesion testing
can detect incompatibilities.
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Coating Compatabilty Patch tests are described in ASTM D5064
Standard Practice for Conducting a Patch Test to Assess Coating
Compatibility and SSPC-Guide 9 Guide for Atmospheric Testing of
Coatings in the Field.
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Coating System/Structure Life Expectancy Expected service life
of structure and coating or overcoat system. Economics of
overcoating versus remaining years of service life.
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Site-Specific Concerns Noise and emission considerations.
Permissible surface preparation and application methods that meet
all requirements and are suitable for the coating product selected.
Return to service time.
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Budget and Time Constraints Some examples: An aliphatic
polyurea cures faster than an acrylic, a good selection when
turnaround time is short and resistance to sunlight is desirable.
An epoxy is less expensive than a polyurethane and works just as
well in interior environments.
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Summary A coating system is applied to a structure to prevent
corrosion and perhaps impart color and gloss. Each layer (primer,
intermediate coat, and/or topcoat) provides a specific protective
function. There are a variety of substrates that are protected
using coatings and coating systems. The various substrates have
inherent characteristics that impact the degree of surface
preparation and coating system selection. A review of coating types
available, substrates, service environment, the condition of the
existing coating system if any, and budget and time constraints are
the means by which the proper coating system can be selected to
provide the maximum corrosion protection.