PAINT BASICS
AND
CORROSION IN METAL
AIA103
Basic Composition of Paint
Solvents (Liquids)
Pigments
Additives
Resins (Binder)
2
Prime Pigments
• Titanium Dioxide (TiO2)
•provides excellent hiding power and whiteness
•available as a solid (powder) or liquid (slurry)
• Zinc Oxide
•controls mildew
•resists ultra-violet light
•resists yellowing
Titanium dioxide is the world's
primary pigment for providing
whiteness, brightness and
opacity.
3
Resins
• Types: Latex, Alkyd, Epoxy, Polyurethane
• Binds or glues ingredients (pigments and
additives) of paint together
• Resin provides adhesion to the substrate
• Resin provides durability & resistance
properties:
• U-V resistance
• Moisture resistance
• Chemical resistance
• Stain resistance
• Fade resistance
• Chalk resistance
• Block resistance
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Gloss/Sheen Levels
• Gloss or Sheen of paint refers to reflectivity or how
shiny the dry paint film is.
• There is lack of standards and confusion in the paint
industry related to gloss or sheen levels.
• Gloss is measured at 60° for flat to gloss ranges.
• Sheen is measures at 85° between flat to eggshell
• Some paint manufacturers use different terms to
define products between flat and semi-gloss: silk,
suede, satin, velvet, eggshell, low sheen, low luster,
pearl, etc.
5
Gloss/Sheen Levels
Term
Gloss @ 60°
Sheen @ 85
Flat
0-5
0-5
Velvet/Low Luster
5-10
5-15
Eggshell
10-20
15-25
Low Sheen
20-30
Semi-Gloss
55-70
Gloss
75+
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Alkyd Resin Technology
ALKYD (Oil-Based)
•
A synthetic resin made by reacting alcohols and fatty acids
•
Soya bean, linseed, tung-oil oil commonly used
•
Benefits of alkyds:
-Superior brushing characteristics
-Abrasion resistance
-Excellent flow and leveling
-Good adhesion
-Used in rust preventative paint
Alkyds have limited availability and use in California.
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Latex Resin Technology
LATEX (water-based)
Synthetic polymers
Main resins
-
100% Acrylic
Styrene Acrylic
Vinyl-Acrylic
Acrylic Copolymer
Vinyl Acetate Ethylene
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Latex Resin Technology
QUALITY Latex paint benefits include:
* Ease of application
* Low odor
* Yellowing resistance
* Color retention
* Chalk resistance
* Gloss retention
* Washability
* Durability
* Good flow & leveling
* Flexibility
* Excellent adhesion
* Scrub resistance
* Improved adhesion
* Water clean-up
9
Acrylic vs. Alkyd Paints
These paints have been exposed to the
elements for 46 years. Over that time,
the PVA (and the alkyd) paints have
disintegrated.
The 100% acrylic paint remains in
remarkably good shape. The paint
film is essentially intact, and, while it
has chalked and faded, it retains its
original green color.
Top left: Alkyd paint
Top right: Vinyl-Acrylic paint
Bottom left: Alkyd paint
Bottom right: 100% acrylic paint
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Acrylic vs. Alkyd Paints
The paint on the left half of each
board is acrylic, the paint on the
right half, an alkyd.
The colors of the paints were
identical when applied. After 15
years of weathering, the
appearance of the alkyds has
changed dramatically.
All have lost gloss, faded, and
chalked. The acrylic paints, in
contrast, have proven remarkably
durable with good color retention.
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Premature Coating Failure
DEFINITION:
The deterioration of the coating system, or corrosion of the
coated surface, more rapidly than would normally be expected
under the service conditions.
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Corrosion
• Simply put, corrosion is created when two dissimilar metals at
atomic levels come into contact with each other and create a
chemical reaction. The new compound is called oxide. In iron it
is called Iron oxide. In aluminum, aluminum oxide and in
copper, copper oxide.
• These metals will not rust or corrode
unless a conductor between the two
metals or atoms is present.
• Water or oxygen in contact with the
metal for a longer period of time is
normally the conductor that starts
the rusting or corrosion process.
Salts in the water will accelerate the
process.
13
Galvanized Metal
• White Rust
• Pure water (rain, dew,
condensation) contain no
dissolved salts or minerals.
Pure water will react with zinc
hydroxide quickly to create
white rust.
• Acid or acid rain, will accelerate
the deterioration of the zinc
finish.
• Passivators are a coating
applied at time of manufacture
to protect the zinc.
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Causes Of Paint Film Failures
(New )
• Faulty Products 2 - 5%
• Unforeseen Circumstance 10-15%
• Improper Specification 25-30%
• Improper Prep/Application 45-55%
15
THERE ARE TWO (2) MAJOR CAUSES
FOR IMPROPER
COATING SPECIFICATIONS
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1. Inadequate or incomplete project
information
2. Lack of product knowledge
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PROJECT INFORMATION
NEEDED…….
18
CUSTOMER
NEEDS
DETERMINE
COATING
SYSTEM
DETERMINE
SURFACE
PREPARATION
EVALUATE
THE
ENVIRONMENT
EVALUATE
SERVICE
REQUIREMENTS
EVALUATE
EXISTING SURFACE
CONDITIONS
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What are the Goals of Surface
Preparation?
To provide a surface suitable for painting by:
• Removing contamination
• Providing a surface profile
• Removing or smoothing irregularities
(pits, projections, sharp edges)
• Removing tightly bound mill scale & rust
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What Surfaces Require
Preparation?
• Iron and Steel
• Galvanized Metal
• Aluminum
• Copper
• Miscellaneous metals
• Pre-Coated Metal Siding
• Previously Painted
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CORROSION !
HOW MUCH ?
22
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Results of Pin Hole Rusting of
the Primer
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What is the Environment?
•
Type – P
•
Type – M
•
Type – C
•
or
•
Type – A
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Type P: Protected Architectural
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Type P: Protected Architectural
•
Not subject to chemical
contaminants
•
Normal humidity range
•
Normal industrial interior
•
Corrosion of steel or galvanized
surfaces negligible
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Type M: Moderate
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Type M: Moderate
• Exterior weathering
• Normal industrial atmosphere
• Moderate concentrations of chemical fumes
• Corrosion of steel < 3 mils / year and
galvanized substrates negligible
• Concentrations of chemical interior –
light to moderate fumes without humidity
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Type C: Corrosive
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Type C: Corrosive
• Moderately aggressive chemical fumes, mists or dust
• Corrosion of steel 3 - 6 mils / year and galvanized
substrates < 1 mil per year
• Adjacent to Type A: but at least
• 30 yards away
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Type A: Aggressively Corrosive
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Type A: Aggressively Corrosive
•
Immersion service
•
Excessive exposure to aggressive chemical
fumes, mists dusts or contaminates
•
Corrosion of steel > 6 mils / year and
galvanized substrates > 1 mil per year
•
Usually confined to an
area within 30 yards
from corrosion source
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Application
• Apply the coating system using one manufacturer
• Apply according to the manufacturer’s recommendations
• Apply to the Dry Film Thickness (DFT) as stated by the
manufacturer
• Recoat within the window specified by the manufacturer
• The finish system shall be a solid uniform finish free of
voids and pinholes.
34
Factors Affecting Coating
Performance
Protection
• Structural Design
(We can’t control)
• Coating Selection
• Surface Preparation
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A Poor Design
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Other Design Considerations
• Surfaces should be smooth (e.g. welds)
• Welding preferred to riveting
• All surfaces should be well drained
• Stiffening members should be on the outside surface of
tank or vessel
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THANK YOU
PROVIDER J476