Surface Preparation and Overcoating
of Factory-Applied Finishes
James D. Machen
KTA-Tator, Inc.
Surface Preparation and Overcoating
of Factory-Applied Finishes –
Overview of Presentation Objectives…
1. Where and why factory
finishes are used
2. Generic types of factory
finishes
3. How to assess the physical
condition of a factory finish
to determine overcoat
viability
Webinar Learning Objectives (con’t)
4. How to prepare a factory
finish for overcoating
5. How to identify candidate
overcoat materials
6. Use of coatings test patch to
validate surface preparation
and overcoat options
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Uses for
Factory-Applied Finishes
• Standing Seam Roof
Panels
• Building Facade Panels
• Canopies
• Awnings
• Curtain Walls
• Railings
• Window Frames/Mullions
• Other Decorative Architectural Metal
4
Metal Substrates to which
Factory Finishes are Applied
• Galvanized sheet metal
– zinc or zinc/aluminum
(trade names such as
Gavalume®, Zincalume®)
• Aluminum sheet metal
• Aluminum extrusions
Sheet metal is typically supplied in “coils” that are coated in
a “coil coating” process.
Extrusions are typically coated by spray application.
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Generic Types of Factory Finishes
•
•
•
•
Fluoropolymers
Polyesters
Silicone modified polyesters
Acrylics
50% to 70% fluoropolymer (PVDF) formulations are
typically superior.
Performance qualities of factory finishes are enhanced by
post baking.
6
Common Factory-Applied Finishes
• ASTM A755/A755M – 11, Standard Specification for Steel
Sheet, Metallic Coated by the Hot-Dip Process and
Prepainted by the Coil-Coating Process for Exterior
Exposed Building Products
– Exposed side – polyester, silicone polyester, acrylic,
fluoropolymer, plastisol, polyurethane
– Interior (protected side) – polyester, acrylic
7
Common Factory-Applied
Finishes (cont.)
• AAMA (Architectural Aluminum Metal Manufacturers
Association) 2603, Voluntary Specification, Performance
Requirements and Test Procedures for Pigmented
Organic Coatings on Aluminum Extrusions and Panels
– Least rigorous of the 3 AAMA standards
– 1 year South Florida Exposure
– Good level of performance and general appearance – typically
interior exposure
– Baked polyester and acrylic
8
Common Factory-Applied
Finishes (cont.)
• AAMA (Architectural Aluminum Metal Manufacturers
Association) 2604, Voluntary Specification, Performance
Requirements and Test Procedures for High Performance
Organic Coatings on Aluminum Extrusions and Panels
–
–
–
–
Middle of the 3 AAMA standards
5 years South Florida Exposure
High level of performance and general appearance
Silicone-modified polyester and 50% polyvinylidene fluoride
(PVDF)
9
Common Factory-Applied
Finishes (cont.)
• AAMA (Architectural Aluminum Metal Manufacturers
Association) 2605, Voluntary Specification, Performance
Requirements and Test Procedures for Superior
Performing Organic Coatings on Aluminum Extrusions
and Panels
–
–
–
–
Most rigorous of the 3 AAMA standards
10 years South Florida Exposure
Superior level of performance and general appearance
70% polyvinylidene fluoride (PVDF)
10
Benefits of
Factory-Applied Finishes
Factory Finishes Provide Excellent……..
• Weathering characteristics
• Color and gloss retention
• Corrosion protection
• Automotive-like finish
• Long term performance
11
Manufacture Warranties
• 10 and 20 year warranties depending on local
exposure conditions:
–
–
–
–
–
Intensity of UV exposure
Airborne pollutants
Chloride, seacoast exposure
Time of wetness
Installation Orientation (vertical vs. low angle)
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Warranties Cover
• Peeling
• Gloss reduction
greater than X
• Color shift
greater than Y
NOTE: Warranties for exterior exposure do not claim
that color and gloss will not shift, but that the shift will
be less than a certain amount compared to original
baseline measurements.
13
Maintenance of Factory Finishes
Maintain as long as possible by……
• Periodic detergent washing
and cleaning
• Cleaning every 6 months
prevents build up of chloride
and acid salts
• Cleaning removes debris that
increases time of wetness
• Clean mildew and fungal
growth at same time (1 gallon
household bleach, cup of
soap, 5 gallons water)
Use Repainting as Last Resort
• Painting introduces risk of
peeling…..
– New coating to factory finish
– Between factory finish and
substrate
• Field-applied coating will not
have the same automotive
look
•
Systematic steps for assessing the condition,
preparing the surface and overcoating factory finishes
are required.
15
Systematic Approach of Assessing Factory
Finishes for Overcoating
Steps Consist of…….
STEP 1 – Determining the Generic Type of Existing Finish
STEP 2 – Assessing the Condition of the Factory Finish
STEP 3 – Preparing the Factory Finish for Overcoating
STEP 4 – Choosing Candidate Overcoat Materials
STEP 5 – Performing a Coatings Test Patch
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STEP 1 – Determine the Generic
Coating Type of Existing Finish
Make Determinations By…….
• Reviewing original specification or project procurement
documents
– Be aware of alternate or substitute products
• Manufacturer’s warranty documents may identify
material suppliers or manufacturers, product trade
names or the shop applicator
– Shops oftentimes use sole source of supply
17
STEP 1 – Determine the Generic
Coating Type of Existing Finish (cont.)
If all else fails…
• Laboratory Analysis to identify generic type
 Infrared
Spectroscopy
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STEP 2 – Assess the Condition of the
Factory Finish
Involves a series of sub-steps to determine the
suitability of the existing factory finish for
overcoating.
• Visual Assessment
 Lifting, Peeling
 Rusting (use SSPC-VIS 2
pictorial standard to
characterize and quantify
rust)
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STEP 2 – Assess the Condition of the
Factory Finish (cont.)
• Paint Thickness
 Determine representative
thickness range
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STEP 2 – Assess the Condition of the
Factory Finish (cont.)
• Adhesion – A “sound foundation” for overcoating
– ASTM D 33359 – Measuring
Adhesion by Tape Test
– ASTM D 6677 – Standard
Test Method for evaluating
Adhesion by Knife Test
– ASTM D 4541 – Standard
Test Method for Pull-Off
Strength of Coatings Using
Portable Adhesion Testers
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STEP 2 – Assess the Condition of the
Factory Finish (cont.)
Knowing the Physical Characteristics of the Existing Coating
Helps to determine Associated Risk Level
• Guidance typically provided by the overcoat material
manufacturer
• Other industry publications and documents
– SSPC-TU 3, Overcoating
22
STEP 3 – Prepare the Factory Finish
for Overcoating
Used to review candidate methods of
surface preparation
• Hand and/or Power
Tool Cleaning
– SSPC-SP 2 or SP 3 to
remove loose
deteriorated coating or
metal oxidation
(corrosion)
– Feather-edge transition
(dull putty knife test)
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STEP 3 – Prepare the Factory Finish
for Overcoating (cont.)
• Pay attention to…..
 Field cut edges
 Field formed surfaces
(tooling damage)
 High foot traffic areas
 Ice damage areas
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STEP 3 – Prepare the Factory Finish
for Overcoating (cont.)
• Overall Surface Cleaning
– Remove dirt/grime/oil/other contaminants by
pressurized water cleaning
– Fan angle of pressurized water – 0, 15, 25
– Be careful not to damage intact coating or substrate
with pressurized water
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STEP 3 – Prepare the Factory Finish
for Overcoating (cont.)
•
Surface Roughening


•
Superficial roughening
only, no coating or
substrate damage
Dull gloss/sheen
Sanding
 Use fine grade of
sandpaper
• Brush-off Blast Clean
– Control process – lower air pressures, use fine/soft
abrasives, increase stand-off distances
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STEP 3 – Prepare the Factory Finish
for Overcoating (cont.)
• Use Less Aggressive Abrasive Media or Methods
– Urethane foam sponge, walnut shells, crushed glass,
fine garnet, other hybrid mixtures
– New low impact technologies utilizing water vapor
and low operating pressures
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STEP 3 – Prepare the Factory Finish
for Overcoating (cont.)
• Goal of Surface Roughening …..
– Provide a uniform and dense surface roughness in a
continuous pattern of peaks and valleys with no
smooth, un-profiled areas.
– Not damage the intact coatings or the underlying
substrate
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STEP 4 – Choose Candidate
Overcoat Materials
Candidate Overcoat Materials Qualities…..
• Compatible with existing factory finish
• Field application friendly
• Good adhesion characteristics
• Suitable for the intended exposure environment
• Capable of producing the desired finish appearance
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STEP 4 – Choose Candidate
Overcoat Materials (cont.)
• Compatibility with Existing Factory Finish is best
determined by……
– Proven history of performance
• Air drying fluoropolymers (FEVE)
• Advanced acrylic formulations
or……
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STEP 5 – Candidate Coating
Test Patches
• Confirms and validates information obtained from previous steps.
• May include evaluation of multiple surface preparation and coating
types
• ASTM D5064, Standard Practice for Conducting a Patch Test to
Access Coating Compatibility
• Test Patch Exposure Time
– Minimum – after full manufacturer curing intervals
– Optimal – 6 mos. to 1 year – cyclic weathering
– Generally, the longer the exposure time, the more useful the
information for predicting risk
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Conclusion
In conclusion, key steps include…
1. Determining the type of the existing finish
2. Assessing the physical characteristics of the existing
finish
3. Reviewing candidate surface preparation methods
4. Reviewing candidate overcoating materials
5. Incorporating information obtained in Steps 1 through
4 into a Coatings Test Patch Program
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Make an Informed Decision
The above steps provide valuable
information for an informed decision.
Process requires…
• Initial expenditure of
– Time
– Money
– Manpower
• Minimizes “guess” work of overcoating
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Surface Preparation and Overcoating
of Factory Applied Finishes
Questions?
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