Specifying and Selecting Coatings
Presented by: Troy Fraebel, Sherwin Williams
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.
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!
Painting Project Specification Contents
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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 Goals
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Clear.
Complete.
Concise.
Consistent.
Correct.
Specification Writing Techniques
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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.
Important Word Meanings
• Shall. Essential requirement.
• Should. Preference or strong recommendation.
• May. Used when alternatives are acceptable.
Coating Specification
Formats
• Construction Specification Institute (CSI)
• SSPC modified CSI format
• Major Sections
– General
– Products
– Execution
Coating System Selection
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Coating mechanisms and types
Type of substrate (steel, concrete, etc.)
Prevailing service environment (immersion?)
Level of surface preparation possible
Access to the work
Owner’s desires and expectations:
• Intended service life of structure
• Desired service life of coating
• Worker skills and equipment availability
• Aesthetics (gloss & color retention)
• Timing
• Economics
Making Steel Corrode
Anode
Cathode
Metallic Pathway
Electrolyte
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.
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
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
Solvent Based Alkyds
• Application as low as 40°F
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Single Package / Ease of Application
Heat Resistance to 200-250 F
Embrittle With Age
Prone to Yellow / Saponify
Require modification for exterior topcoats
Waterborne Acrylics
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Single Component Water Based
Fast dry and fast re-coat
Good color and gloss retention
Primers must contain inhibitors
Low stress
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
Moisture Cured Urethanes
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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
Types of Substrates Coated
Types of Steel
• Cold-rolled
• Hot-rolled
• Stainless steel
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.
Hot-Rolled Steel
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Typical of structural steel used
in construction.
Manufacturing process creates
a bonded layer of iron oxide
called mill scale.
• Smooth
• Cathodic
• Differential expansion
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)
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.
Aluminum
• May require chemical treatment, wash
priming, and/or brush off blasting with a
soft abrasive.
• SSPC-SP 16
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.”
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.
Concrete Characteristics
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Alkalinity (pH range of 9 to 12)
Porosity
Moisture
Movement of concrete (i.e., cracking)
Concrete Types and Finishes
• Concrete (tilt-up, cast-in-place, block)
• Finish (broom, steel trowel, sacked,
stoned, wood floated)
• Curing compounds / Sealers
(paintable?)
Other Substrates
• Wood or plywood
• Polyvinyl Chloride (PVC)
• Fiberglass Reinforced Plastic
(FRP)
Demands of Environments on
Coating Systems
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?
Questions to Ask
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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 climatecontrolled shop environment or in the field?
• What is the surface temperature during
application?
Interior Service Environment Coatings
• Coatings need not
withstand sunny
conditions.
• Maybe climate controlled.
Exterior Service Environment Coatings
• Designed to withstand sun,
rain, and snow.
• Remain flexible after curing;
won’t crack or peel as it
expands and contracts with
changes in temperature and
humidity.
• Additives enhance mildew-,
fungus-, and UV-resistance.
Service Locations
• What are some different service locations?
• How might location affect the type of
coating you would select?
• What factors should be considered?
Inland, Rural
• Free from the
corrosive influence of
airborne salt; polluted
air and rain may still
be present.
Heavy Industrial
• High corrosion rates
• High atmospheric chemical concentration
(i.e., sulphur dioxide, nitrous oxide)
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.
Immersion
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Better surface preparation.
More impermeable.
Typically not UV stable.
Must resist constant
exposure to the cargo.
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.
Condensing Humidity Service
• Example:
• Headspace in a tank
• Indoor pool with condensation on
ceiling
• Cold pipes
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.
Underground
• Buried surfaces in
direct contact with
soil.
• Possibly highly
acidic.
• Compatible with
cathodic protection.
Abrasion and Impact
• Coatings exposed to particle objects that
rub, scrape, impact, or erode the surface
by friction (i.e., pipeline, dam gate).
Final Service Temperature
• Certain coatings are prone to limited
chemical resistance and early failure when
exposed to high in-service temperatures.
Other Factors to Consider
• What else might impact your choice of
coating selection beyond the service
environment?
Application Temperature
• Apply coating system only when the air
and substrate temperature are within the
range indicated by the manufacturer’s
written instructions on the product data
sheet (PDS).
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 5oF (3oC) above the dew point.
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!
Adhesion
• Test adhesion of existing coating to itself
and to the substrate.
• Low adhesion values can indicate possible
delamination during overcoating.
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.
Chalking and Erosion
• Typical of aging epoxy and alkyd coatings.
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.
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.
Coating System/Structure Life
Expectancy
• Expected service life of structure and
coating or overcoat system.
• Economics of overcoating versus remaining
years of service life.
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.
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.
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.
???????ANY QUESTIONS ????????