SSPC-Paint 38
March 1, 2012
Edtorial Revision September 13, 2013
SSPC: The Society for Protective Coatings
Coating Standard No. 38
Single-Component Moisture-Cure Weatherable Aliphatic
Polyurethane Topcoat, Performance-Based
1. Scope
3.4 ASTM STANDARDS:2
1.1 This standard contains performance requirements
for a high-performance, single-component, moisture-curing
UV-stable polyurethane topcoat (ASTM D 16, Type II polyurethane) for use on steel substrates. The coating is intended to be
used as a topcoat that provides good color and gloss retention.
D 16
D 523
* D 562
1.2 Coatings meeting the requirements of this standard
are generally suitable for exposures in SSPC Environmental
Zones 1A (interior, normally dry), 1B (exterior, normally dry),
2A (frequently wet by fresh water, excluding immersion), 2B
(frequently wet by salt water, excluding immersion), 3B (chemical exposure, neutral) and 3C (chemical exposure, alkaline)1.
D 1014
* D 1296
1.3 The coating is intended for application by brush, spray,
or roller over a primer or intermediate coating.
* D 1475
2. Description
* D 1535
2.1 This single-package moisture-curing polyurethane
coating is characterized by the presence of free polyisocyanate
groups capable of reacting with atmospheric moisture in order
to form a film.
* D 1640
D 2244
2.2 WEATHERING LEVELS: This standard contains three
levels of accelerated (A) and South Florida weathering (SF)
performance described in Section 7.2.
* D 2369
3. Referenced Standards
* D 2371
3.1 The latest issue, revision, or amendment of the referenced standards in effect on the date of invitation to bid shall
govern, unless otherwise specified. Standards marked with
an asterisk (*) are referenced only in the Notes, which are not
requirements of this standard.
* D 2621
3.2 If there is a conflict between the requirements of any of
the cited referenced standards and this standard, the requirements of this standard shall prevail.
D 2794
* D 2697
D 4214
3.3 SSPC STANDARD:
Guide 13
1
Guide for the Identification and Use of
Industrial Coating Materials in Computerized Product Databases
2
SSPC Environmental Zones are defined in “About SSPC Standards
and Guides” available online from <http://www.sspc.org>.
1
Standard Terminology for Paint, Related
Coatings, Materials, and Applications
Standard Test Method for Specular
Gloss
Standard Test Method for Consistency of Paints Measuring Krebs Units
(KU) Viscosity Using the Stormer-Type
Viscometer
Standard Practice for Conducting Exterior Exposure Tests of Paints and
Coatings on Metal Substrates
Standard Test Method for Odor of Volatile Solvents and Diluents
Standard Test Method for Density of
Liquid Coatings, Inks, and Related
Products
Standard Practice for Specifying Color
by the Munsell System
Standard Test Methods for Drying,
Curing, or Film Formation of Organic
Coatings at Room Temperature
Standard Test Method for Calculation of
Color Tolerances and Color Differences
From Instrumentally Measured Color
Coordinates
Standard Test Method for Volatile
Content of Coatings
Standard Test Method for Pigment
Content of Solvent-Reducible Paints
Standard Test Method for Infrared
Identification of Vehicle Solids from
Solvent-Reducible Paints
Standard Test Method for Volume
Nonvolatile Matter in Clear or Pigmented
Coatings
Standard Test Method for Resistance of
Organic Coatings to the Effects of Rapid
Deformation (Impact)
Standard Test Methods for Evaluating
Degree of Chalking of Exterior Paint
Films
ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA
19428-2959. For referenced ASTM standards, visit the ASTM website,
www.astm.org, or contact ASTM Customer Service at service@astm.
org. For Annual Book of ASTM Standards volume information, refer to
the standard’s Document Summary page on the ASTM website.
SSPC-Paint 38
March 1, 2012
Editorial Revision September 13, 2013
D 4541
D 4587
D 5402
G 154
5.2 APPLICATION PROPERTIES: All guidance provided by
the manufacturer regarding thinning requirements and special
application requirements shall be followed (see Note 11.3). The
coating shall be easily applied by brush, roller, or spray in accordance with the manufacturer’s written instructions. The coating
shall have no streaking, running, or sagging or other defects
during application or while drying.
Standard Test Method for Pull-Off
Strength of Coatings Using Portable
Adhesion Testers
Standard Practice for Fluorescent
UV-Condensation Exposures of Paint
and Related Coatings
Standard Practice for Assessing the
Solvent Resistance of Organic Coatings
Using Solvent Rubs
Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of
Nonmetallic Materials
6. Test Panel Preparation
Triplicate test panels shall be prepared for each test. Prior
to application of the topcoat to be tested, a compatible primer
and intermediate coat recommended by the manufacturer of the
topcoat to be tested shall be applied to the panels and cured
in accordance with the manufacturer’s written instructions. The
topcoat to be tested shall be applied according to the manufacturer’s written recommendations.
3.5 AMERICAN NATIONAL STANDARDS INSTITUTE
(ANSI) STANDARD:3
Z129.1
Hazardous Industrial
Precautionary Labeling
Chemicals
–
7. Weathering Requirements
3.6 AMERICAN ASSOCIATION OF STATE HIGHWAY AND
TRANSPORTATION OFFICIALS (AASHTO) STANDARD:4
TP 67-03
7.1 WEATHERING RESISTANCE: Two weathering test
procedures are defined below. Performance levels are established using whites and light colors. It is left to the discretion of
the specifier whether to accept Florida data from a similar color
or to use UV-A data in lieu of South Florida weathering data.
[NOTE: Commercial test sites in North America conforming to
this requirement are located in southern Florida and Arizona.]
Standard Method of Test for Analysis of
Structural Steel Coatings for Isocyanate
Content
4. Composition Requirements
4.1 RESIN REQUIREMENT: The resin used in the coating
shall be a polyisocyanate-based product that cures through a
chemical reaction with atmospheric moisture. Use of other resins
or modifiers shall be minimal and limited to products necessary
for formula ingredient compatibility and to improve recoating
properties. Manufacturer’s formulations of single-component
moisture-curing weatherable polyurethane topcoats normally
contain levels of polyisocyanate in vehicle solids above 3.5% by
weight, as determined by AASHTO TP 67-03.
7.1.1 Accelerated Weathering: Accelerated weathering
shall be performed in accordance with ASTM D 4587, Cycle 2.
Apparatus – Fluorescent UV/condensation apparatus
complying with ASTM G 154.
TABLE 1
TIME CORRESPONDING TO EACH PERFORMANCE LEVEL
Performance
Level
4.2 VOC CONTENT: See Note 11.1 for information on VOC
content.
4.3 ANALYTICAL TEST DATA: If required, the coating
manufacturer shall provide certificates of analysis for coating
batches qualified by independent testing to meet this standard
for use in verifying batch-to-batch consistency of material (see
Note 11.2 and subsections)
*
5. Requirements of Liquid Coating
Hours to
Noticeable Change*
Cycles to
Noticeable Change*
Accelerated UVA/Condensation
Level 1
500 to 1000
63 to 125
Level 2
1001 to 2000
126 to 250
Level 3
2001 or more
251 or more
Noticeable change following Accelerated UV-A/Condensation testing
is defined as a gloss reduction of 25% or more of the initial gloss
value measured at a 60° angle or a color change greater than 3.0
∆E* (see Section 7.2.1).
TABLE 2
SOUTH FLORIDA WEATHERING PERFORMANCE
5.1 STORAGE STABILITY: The coating shall exhibit no
curdling, gelling, gassing, or hard caking after being stored
unmixed for a minimum of 180 days in a tightly sealed, unopened
container at a temperature of 25 degrees C (77 degrees F).
Performance Level
Level 1
Level 2
Level 3
American National Standards Institute, 1819 L Street, NW, Suite 600,
Washington, DC 20036. Standards available online from www.ansi.
org
4
American Association of State Highway and Transportation Officials,
444 North Capitol Street, NW, Suite 249, Washington DC 20001,
202-624-5800. Standards available online at https://bookstore.transportation.org
3
Months to Noticeable Change*
12 to 23
24 to 47
48 or more
* Noticeable change following Florida exposure testing is defined as a
gloss reduction of 35% or more of the initial gloss value measured at a
60° angle or a color change greater than 3.0 ∆E* (see Section 7.2.1).
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SSPC-Paint 38
March 1, 2012
Edtorial Revision September 13, 2013
TABLE 3
SUMMARY OF PERFORMANCE TESTING RESULTS FOR COLOR AND GLOSS RETENTION
Measurement Test/Evaluation Criteria
Exposure Test
†
Performance Level
Exposure Time
Accelerated
Weathering (A)
(Section 7.1.1.)
Level 1A
500 h
Level 2A
1000 h
Level 3A
2000 h
South Florida
Weathering (SF)
(Section 7.1.2)
ASTM D 1014
Level 1 SF
12 mo
Level 2 SF
24 mo
Level 3 SF
48 mo
Color Retention
ASTM D 2244
Maximum Gloss
Reduction
ASTM D 523
Color Change
≤3.0 ΔE
C.I.E. 1976 L*A*B*†
25% from
original reading
Color Change
≤3.0 ΔE
C.I.E. 1976 L*A*B*†
35% from
original reading
Smaller values of color change (less than 3.0 ∆E*) may be visible, but the noticeable change maximum of 3.0 ∆E* required by this standard is
acceptable for most industrial and marine applications. The specifier has the option to require more stringent gloss and color retention.
according to ASTM D 523. Table 3 summarizes the tests of
Section 7 as well as the minimum acceptance criteria. See Note
11.4 regarding test results for darker colors.
Procedure –Test according to ASTM D 4587 Cycle 2
procedure. This eight-hour duration comprises one test cycle.
Continue cycle testing to achieve the exposure hours defined in
the required performance levels (as shown in Table 1).
8. Laboratory Physical Tests of Applied Coatings
Smaller values of color change (less than 3.0 ∆E*) may be
visible, but the noticeable change maximum of 3.0 ∆E* required
by this standard is acceptable for most industrial and marine
applications. The specifier has the option to require more stringent gloss and color retention.
8.1 RECOATABILITY: Intercoat and substrate adhesion
properties of the polyurethane topcoats shall be determined by
measurement of adhesion values between:
a) primer and the substrate,
b) polyurethane topcoat and the primer or intermediate
coat, and, if applicable
c) the second coat of polyurethane topcoat and the same
previously applied topcoat.
Coating manufacturers shall provide acceptable window (time
frame) ranges between applications of coats in a multi-coat
system. Unless the purchaser specifically requests a variance,
the maximum dry film thickness and the minimum curing time
(with reported conditions for temperature and humidity) as
stated on the manufacturer’s product data sheets will be used
for coating application prior to adhesion testing. All testing shall
be performed on a minimum of three steel test panels each with
minimum dimensions of 75 x 150 x 6 mm (3 x 6 x ¼ inches). The
panels shall be prepared to the minimum surface preparation
recommendations of the coating manufacturer.
7.1.2 South Florida Weathering: South Florida weathering shall be performed in accordance with ASTM D 1014 (45˚
south exposure, washed with mild detergent before readings
are taken).
7.2 Performance Levels: Tables 1 and 2 specify the
amount of time the coating must perform before noticeable
change in order to achieve the defined performance level.
Polyurethane topcoats are available in a wide range of color
and gloss. Procurement documents shall state the desired
level of performance, exposure method (in accordance with
Tables 1 and 2), color, and gloss. For example, a specifier may
require Level 2SF Florida exposure, initial gloss greater than
80, matched to a specific color. A certain level of accelerated
weathering does not necessarily correspond to a particular level
of atmospheric weathering and they need to be specified independently. These are two independent complementary tests for
measuring coating performance. If no level is specified, either
Accelerated Level 3 or South Florida Level 3 data is acceptable.
The coating manufacturer shall report the type of testing used to
generate the data.
8.2 ADHESION
8.2.1 Primer Adhesion to Steel Substrate: Apply the
primer to the steel panel and cure according to the manufacturer’s recommendations. Test adhesion according to ASTM D
4541 and identify the type of adhesion tester used (Type II, III,
IV, or V). The minimum adhesion acceptance value of the primer
to the substrate shall be 4.1 MPa (or 600 psi in U.S. units).
7.2.1 Each replicate panel must meet the minimum acceptance criteria. Clear coatings must be tested over the intended
basecoat. Initially, and at the end of the exposure period for
each level, tristimulus color values shall be measured according
to ASTM D 2244, and 60 degree gloss shall be measured
8.2.2 Polyurethane Topcoat Adhesion to the Primer:
Apply topcoat to panels (previously primed as described in 8.2.1)
and cure according to the manufacturer’s recommendations.
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SSPC-Paint 38
March 1, 2012
Editorial Revision September 13, 2013
TABLE 4
ADDITIONAL REQUIRED PERFORMANCE PROPERTIES
TEST
Adhesion (to substrate,
primer, intermediate coat, or
previously applied topcoat)
(Section 8.2 and subsections)
ASTM METHOD
RESULT (UNITS)
MINIMUM
ACCEPTABLE VALUE
D 4541
MPa (psi)
4.1 (600)
Direct Impact Resistance
(Section 8.4)
D 2794
kg-force per square
centimeter
(lb-force per square inch)
4.2 (60)
Solvent (MEK) Resistance
(Section 8.5)
D 5402
Number of double-rubs
4 sets of 25 with no
topcoat visible on cloth
Evaluating degree of chalking
in exterior paints (Section 8.6)
D 4214
Photographic standard rating method
6, where 10 is no chalking*
* At desired weathering level.
9. Labeling
Test the intercoat adhesion between topcoat and primer or
intermediate coat in accordance with ASTM D 4541 and identify
the type of adhesion tester used. Intercoat adhesion is defined
as the force required to separate the topcoat from the underlying coat. The minimum intercoat adhesion (both adhesive and
cohesive) shall meet or exceed the cohesive strength of the
coating.
9.1 Labeling shall conform to ANSI Z129.1
9.2 Technical data shall be provided for at least all data
elements categorized as “essential” in SSPC-Guide 13. The
specifier has the option to require additional data to satisfy
quality assurance or local regulatory requirements.
8.2.3 Polyurethane Topcoat Adhesion to (Same) Previously Applied Topcoat: Apply a second coat of topcoat and
cure according to the manufacturer’s recommendations. Test
the intercoat adhesion in accordance with ASTM D 4541 and
identify the type of adhesion tester used. The minimum intercoat adhesion (both adhesive and cohesive) shall meet or
exceed the cohesive strength of the coating.
10. Disclaimer
10.1 While every precaution is taken to ensure that all
information furnished in SSPC standards and specifications is
as accurate, complete, and useful as possible, SSPC cannot
assume responsibility nor incur any obligation resulting from
the use of any materials, coatings, or methods specified herein,
or of the specification or standard itself.
8.3 Polyurethane topcoat cohesion (bond strength within
a single layer of coating) shall be equal to or greater than the
minimum acceptable intercoat adhesion
10.2 This specification does not attempt to address problems concerning safety and health associated with its use. The
user of this specification, as well as the user of all products or
practices described herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance
with all governmental regulations.
8.4 Direct Impact Resistance: The minimum impact
resistance of the cured topcoat as applied to 3 test specimens
shall be 4.2 kilograms of force (kg-force) per square centimeter
(or 60 pounds of force per square inch [in-lb] in U.S. units) when
measured in accordance with ASTM D 2794.
11. Notes
8.5 Solvent (MEK) Resistance: Using a test cloth saturated with MEK following procedures in ASTM D 5402, no
topcoat shall be visible on the test cloth after four sets of 25
double-rubs.
Notes are not requirements of this specification.
11.1 VOC CONTENT: Local regulations regarding VOC
content, VOC emissions, and container labeling may vary
depending on project location. For example, U.S Federal limits
for VOCs in industrial maintenance coatings were published in
1998 and may be found at <http://www.epa.gov/ttn/atw/183e/
aim/aimpg.html#RULE>.
These limits apply to the coating at the time of application,
after thinning according to the manufacturer’s recommendations.
8.6 Resistance to Chalking: When evaluated in accordance with procedures in ASTM D 4214 Test Method A at the
time period indicated for desired weathering level, maximum
chalking value shall be a level of 6 using Reference Photograph
No. 1.
These properties are summarized in Table 4.
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SSPC-Paint 38
March 1, 2012
Edtorial Revision September 13, 2013
However, many state and local governments and/or air quality
management areas have more stringent VOC regulations than
those in the federal rule. In the U.S., information on the VOC
content of each container before mixing or thinning is found
on the container label and in the manufacturer’s safety data
sheet. The coating manufacturer’s product data sheet usually
provides information on the total VOC content of a coating after
mixing and any recommended thinning.
material. The pass/fail criterion is that the measurement of the
test sample shall fall within two standard deviations of the target
value. The contracting parties must agree on a target value.
11.2.2 Quality Assurance Testing Procedures: Quality
assurance tests include but are not limited to: infrared analysis
(ASTM D 2621), viscosity (ASTM D 562), weight per gallon
(ASTM D 1475), total solids (ASTM D 2369), volume solids
(ASTM D 2697), dry time (ASTM D 1640), percent pigment
(ASTM D 2371), gloss (ASTM D 523), color (ASTM D 1535,
ASTM D 2244), odor (ASTM D 1296), and isocyanate content
(AASHTO TP 67-03).
11.2 QUALITY ASSURANCE TESTS: Quality assurance
tests are used to determine whether the supplied products are
of the same type and quality as those originally tested. The
selected tests should rapidly and accurately measure the physical and chemical characteristics of the coating necessary to
verify that the supplied material is substantially the same as the
previously accepted material. All of the quality assurance tests
must be performed on the originally submitted qualification
sample. The results of these tests are used to establish pass/
fail criteria for quality assurance testing of supplied products.
11.3 These coatings may be susceptible to pinholing if
applied under adverse conditions such as high humidity. The
degree of pinholing depends on formulation variables. Consult
the coating manufacturer’s recommendations for formulation
additives that may be used to address this problem.
11.4 Test results for color and gloss of deeper colors (i.e.,
having a Munsell value below 9) will vary significantly due to
differences in pigment weathering properties, and may not
meet the requirements of Section 7 without use of additional
procedures such as clear coating. Alternatively, the specifier
may accept a greater change in gloss and color for deeper
colors.
11.2.1 Establishing Quality Assurance Acceptance
Criteria: Many ASTM test methods contain precision and bias
statements. Specification developers should be cognizant of the
fact that these statements exist. Quality assurance test criteria
should not be more stringent than the interlaboratory precision
of the test methods used. The specifier may require additional
technical data to satisfy QA or local regulatory requirements.
Where precision and bias data are not available for a given
test method, determine the standard deviation of a minimum of
five measurements taken on the originally tested and certified
The coating manufacturer should be contacted if the
user desires color change of less than 2.0 ∆E* for a specific
application. In order to achieve this requirement, additional
procedures such as clear coating may be needed.
Copyright ©
SSPC standards, guides, and technical reports are copyrighted
world-wide by SSPC: The Society for Protective Coatings. Any
photocopying, re-selling, or redistribution of these standards,
guides, and technical reports by printed, electronic, or any other
means is strictly prohibited without the express written consent
of SSPC: The Society of Protective Coatings and a formal
licensing agreement.
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