ASTM C581-20

Standard Practice for Determining Chemical Resistance of Thermosetting Resins Used in Glass-Fiber-Reinforced Structures Intended for Liquid Service

SIGNIFICANCE AND USE
4.1 The results obtained by this practice shall serve as a guide in, but not as the sole basis for, selection of a thermosetting resin used in an RTP structure. No attempt has been made to incorporate into the practice all the various factors that will potentially affect the serviceability of an RTP structure when subjected to chemical environments. These factors will potentially include stress, different resin-to-glass ratios, and multiple veils.
SCOPE
1.1 This practice is designed to evaluate, in an unstressed state, the chemical resistance of thermosetting resins used in the fabrication of reinforced thermosetting plastic (RTP) laminates. This practice provides for the determination of changes in the properties, described as follows, of the test specimens and test reagent after exposure of the specimens to the reagent: hardness of specimens, weight change thickness, appearance of specimens, appearance of immersion media, and flexural strength and modulus.  
1.1.1 This practice is also useful to evaluate other factors, such as surfacing veils and the effect of resin additives, on the chemical resistance of the resin.  
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
Note 1: There is no known ISO equivalent to this standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Feb-2020
• ICS: 83.120 - Reinforced plastics
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.23 - Reinforced Thermosetting Resin Piping Systems and Chemical Equipment

Relations

• Replaces: ASTM C581-15 - Standard Practice for Determining Chemical Resistance of Thermosetting Resins Used in Glass-Fiber-Reinforced Structures Intended for Liquid Service
• Effective Date: 15-Feb-2020
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM D2584-18 - Standard Test Method for Ignition Loss of Cured Reinforced Resins
• Effective Date: 15-Sep-2018
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017
• Refers: ASTM D790-17 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Jul-2017
• Refers: ASTM D790-15e1 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Dec-2015
• Refers: ASTM D790-15 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Dec-2015
• Refers: ASTM D2563-08(2015) - Standard Practice for Classifying Visual Defects in Glass-Reinforced Plastic Laminate Parts (Withdrawn 2024)
• Effective Date: 01-Sep-2015

Overview

ASTM C581-20 is a recognized standard practice developed by ASTM International, providing guidance for determining the chemical resistance of thermosetting resins used in glass-fiber-reinforced structures for liquid service. This standard is widely used within industries that employ reinforced thermosetting plastic (RTP) laminates, especially in applications exposed to potentially corrosive or aggressive chemical environments. The practice is designed to evaluate, in an unstressed state, critical changes in properties such as hardness, weight, thickness, appearance, and mechanical characteristics (flexural strength and modulus) when RTP laminates are subjected to chemical exposure.

This method helps engineers, material specifiers, and manufacturers compare thermosetting resin candidates for use in composite structures like tanks, pipes, and chemical equipment. While it serves as an important reference for chemical resistance testing, ASTM C581-20 should not be the sole factor in material selection, as actual performance may vary based on real-world installation and service conditions.

Key Topics

• Chemical Resistance Evaluation: The practice measures how thermosetting resins and glass-fiber-reinforced laminates respond to extended exposure in various chemical environments. Key properties monitored include Barcol hardness, weight and thickness changes, and flexural properties.
• Specimen Preparation: Standardized procedures for preparing, curing, and testing RTP laminate specimens ensure consistent and comparable results.
• Immersion Testing: Samples are fully immersed in selected test reagents at controlled temperatures for specified periods, with physical and mechanical property changes tracked over time.
• Visual and Mechanical Assessment: Regular inspection for surface degradation, loss of gloss, blistering, or other irregularities are critical to detecting material deterioration.
• Reporting and Data Analysis: The standard outlines detailed requirements for recording test variables, pre- and post-test observations, and summarizing results through graphical representation of retained properties.
• Limitations: While valuable, this practice does not cover all factors influencing the real-world serviceability of RTP structures, such as mechanical stresses, resin-to-glass ratio variations, and use of surfacing veils.

Applications

The ASTM C581-20 standard is utilized across a range of sectors to support material selection and qualification:

• Chemical Processing: Critical in verifying the suitability of glass-fiber-reinforced resin tanks, pipes, and process equipment where extended chemical exposure occurs.
• Water and Wastewater Treatment: Used to test and select resins for composite piping and storage systems in environments exposed to aggressive liquids.
• Industrial Manufacturing: Supports the development and quality assurance of glass-reinforced plastic components subjected to corrosive substances.
• Material Qualification: Facilitates the comparison of new resin formulations, additives, or surfacing veils by providing a consistent framework for chemical resistance testing.
• Compliance and Specification: Helps manufacturers and design engineers meet industry standard requirements and document chemical resistance as part of project submittals.

Related Standards

ASTM C581-20 references several other ASTM standards relevant to plastics and composite laminate testing, including:

• ASTM D790: Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• ASTM D883: Terminology Relating to Plastics
• ASTM D2563: Practice for Classifying Visual Defects in Glass-Reinforced Plastic Laminate Parts
• ASTM D2583: Test Method for Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor
• ASTM D2584: Test Method for Ignition Loss of Cured Reinforced Resins

Currently, there is no known ISO equivalent for ASTM C581-20, making it a key international reference for evaluating chemical resistance in glass-fiber-reinforced thermosetting resins.

By deploying this standard, industry professionals can make informed decisions, ensure product durability, and maintain compliance with recognized international testing practices for chemical resistance in glass-fiber-reinforced composite materials.

Keywords: chemical resistance, thermosetting resins, glass-fiber-reinforced plastic, RTP laminates, ASTM C581-20, composite materials, chemical exposure testing, industrial standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C581 − 20
Standard Practice for
Determining Chemical Resistance of Thermosetting Resins
Used in Glass-Fiber-Reinforced Structures Intended for
Liquid Service
This standard is issued under the fixed designation C581; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
1.1 This practice is designed to evaluate, in an unstressed 2.1 ASTM Standards:
state, the chemical resistance of thermosetting resins used in D790 Test Methods for Flexural Properties of Unreinforced
the fabrication of reinforced thermosetting plastic (RTP) lami- and Reinforced Plastics and Electrical Insulating Materi-
nates. This practice provides for the determination of changes als
in the properties, described as follows, of the test specimens D883 Terminology Relating to Plastics
and test reagent after exposure of the specimens to the reagent: D2563 Practice for Classifying Visual Defects in Glass-
hardnessofspecimens,weightchangethickness,appearanceof Reinforced Plastic Laminate Parts
specimens, appearance of immersion media, and flexural D2583 Test Method for Indentation Hardness of Rigid Plas-
strength and modulus. tics by Means of a Barcol Impressor
1.1.1 This practice is also useful to evaluate other factors, D2584 Test Method for Ignition Loss of Cured Reinforced
such as surfacing veils and the effect of resin additives, on the Resins
chemical resistance of the resin.
3. Terminology
1.2 The values stated in inch-pound units are to be regarded
3.1 Definitions of Terms:
as standard. The values given in parentheses are mathematical
3.1.1 For definitions of terms associated with plastic
conversions to SI units that are provided for information only
and are not considered standard. materials, see Terminology D883.
NOTE 1—There is no known ISO equivalent to this standard.
4. Significance and Use
1.3 This standard does not purport to address all of the
4.1 The results obtained by this practice shall serve as a
safety concerns, if any, associated with its use. It is the
guide in, but not as the sole basis for, selection of a thermo-
responsibility of the user of this standard to establish appro-
setting resin used in an RTP structure. No attempt has been
priate safety, health, and environmental practices and deter-
madetoincorporateintothepracticeallthevariousfactorsthat
mine the applicability of regulatory limitations prior to use.
will potentially affect the serviceability of an RTP structure
1.4 This international standard was developed in accor-
when subjected to chemical environments. These factors will
dance with internationally recognized principles on standard-
potentially include stress, different resin-to-glass ratios, and
ization established in the Decision on Principles for the
multiple veils.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
5. Apparatus
Barriers to Trade (TBT) Committee.
5.1 HardnessTestingInstrument—Thisshallbeasdescribed
in Test Method D2583.
ThispracticeisunderthejurisdictionofASTMCommitteeD20onPlasticsand
is the direct responsibility of Subcommittee D20.23 on Reinforced Plastic Piping
Systems and Chemical Equipment. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Feb. 15, 2020. Published March 2020. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1965. Last previous edition approved in 2015 as C581 – 15. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C0581-20. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C581 − 20
5.2 Flexural Properties Testing Apparatus, in accordance 7.2.1 Laminate Size—A suitable laminate size has been
with Test Methods D790. found to be 26 by 33 in. (660 by 838 mm) after trimming. This
laminate size is not restrictive and other dimensions are
5.3 Thickness Measurement—A micrometer suitable for
acceptable.
measurement to 0.001 in. (0.025 mm).
7.2.2 Thickness—The thickness of the cured standard lami-
5.4 Containers, of sufficient size, capacity, and inertness to
nate shall be between 0.120 and 0.140 in. (3.05 and 3.56 mm).
allow total immersion of reinforced thermosetting plastic
7.2.3 Reinforcement Content—The glass fiber and binder
2 2
specimens in the specific corrosives chosen for testing. These
shall be 4.73 6 0.47 oz/ft (three layers of 1.5 oz/ft chopped
containers shall, when necessary, be capable of maintaining
strand mat 4.5 oz/ft having a nominal binder content of 3.5 %
liquid levels of volatile solutions, that is, solvents. This can be
and two layers of 10 mil surfacing mat 0.23 oz/ft having a
accomplished by the use of reflux condensers.
nominal binder content of 7 %)—determined by pre-weighing
the materials prior to construction of the laminate. This is
5.5 Heating Apparatus—Aconstant temperature oven, heat-
equivalent to 23.6 weight % (12.5 volume %) glass fiber when
ing mantle, or liquid bath capable of maintaining temperature
using a resin having a cured specific gravity of 1.15. Such a
within range of 64.0°F (62.2°C). Take proper precautions if
laminate will have a thickness of 0.125 in. (3.18 mm). The use
the corrosives selected are flammable liquids.
of resins having different specific gravities will result in
5.6 Analytical Balance, suitable for accurate weighing to
different weight percentages of glass fiber, but the volume
0.001 g.
percentage of glass fiber will remain the same. When using
synthetic organic fiber surfacing veil, the glass content shall be
2 2
6. Reagents
4.50 6 0.45 oz/ft (three layers of 1.5 oz/ft chopped strand
mat having a nominal binder content of 3.5 %).
6.1 The test media shall consist of the reagents or solutions
7.2.4 Hardness—The hardness shall be at least 90 % of that
to which the RTP laminates are to be exposed.
of a fully-cured clear casting of the resin, or of a similarly
constructed laminate as defined by the resin manufacturer.
7. Test Specimens
Hardness shall be determined in accordance with s5.1. Note
7.1 Standard Laminates—Prepare standard fiber-reinforced
that the use of synthetic veil will result in significantly lower
laminates using identical reinforcement in all of the laminates.
hardness values. The hardness value will vary with the type of
The laminates shall be constructed of the following materials:
resin and number of plies of synthetic veil. The resin manu-
7.1.1 Surfacing Mat (Veil)—A thin mat of fine fibers used
facturer needs to be contacted for the allowable Barcol
primarily to produce a smooth, resin-rich surface on a rein-
hardnessvalueofalaminatecontainingsyntheticveilswiththe
forced plastic.The surfacing veil helps determine the thickness
specific resin.
of the resin-rich layer, reduces microcracking and provides a
7.2.5 Laminate Condition—The laminate shall meetAccep-
non-wicking chemically–resistant layer. The surfacing veil
tance Level I of Table I of Practice D2563.
shall be compatible with the resin and manufactured with
7.3 Fabrication of Standard Laminate—The sequence of
uniform fiber distribution and non-bundled fibers. The dry veil
lay-up shall be as follows:
layer(s) shall be a minimum 10 mils in thickness and produce
7.3.1 Apply catalyzed resin and a 10-mil (0.25-mm) surfac-
a 10 to 15 mil resin-saturated veil layer per 10 mils of dry veil.
ing mat on a flat surface covered with plastic release film or
To eliminate the surfacing veil as a variable in corrosion tests,
treated with a suitable release agent and roll to distribute resin.
prepare each laminate within a test group with the same
surfacing veil.
NOTE 3—Use the following formula as a guide to determine the total
weight of resin to be used.This is equivalent to 12.5 volume % glass fiber
7.1.2 Chopped Strand Mat—Type E glass fiber with sizing
in the laminate. Grams resin equals grams glass fiber material per 7.2.3
and binder compatible with the resin. It is acceptable to use
times 2.82 G. Where G equals specific gravity of cured resin. It is
other glass fiber compositions, but using such alternate com-
acceptable to use excess resin due to loss by adhering to mixing
positions shall be considered as variables for comparison to the
containers, rollers, and other factors. A suggested amount of excess resin
is 10 to 15 % by weight.
standard.
7.1.2.1 Note that this practice applies to E-CR glass fiber,
7.3.2 Follow with three plies of 1.5 oz/ft chopped strand
which is a type of E glass fiber. If the E glass fiber material is
mat and resin. Roll after each ply to distribute and wet-out the
of the E-CR type that information shall be identified in the test
chopped strand mat. Rolling with a serrated roller is acceptable
report.
after each ply to remove entrapped air but it shall be done in
7.1.3 Resin—Catalyzed and promoted in accordance with accordancewith7.3.4.Thematweightshallbewithin 65%of
the resin manufacturer’s recommendation. 1.5 oz/ft upon weighing the full 26 by 33-in. cut (660 by
838-mm) piece, (or other full dimension used, 7.2.1.).
NOTE 2—It is acceptable to add fillers, such as antimony trioxide for
improved fire performance or thixotropes for viscosity control, but it is
NOTE 4—Cut chopped strand mat so that the 26-in. dimension is across
possible that this will detract from the corrosion resistance of the test
the width of the roll and the 33-in. dimension is along the machine
laminate.
direction of the mat. Mat weight variation will most commonly occur
across the width of the mat. If a wide roll of mat, 52 in. (1320 mm) or
7.2 Dimensions and General Properties—The laminates
greater, is used, place the two plies of mat in the laminate such that the
shall conform to the required dimensions and general proper-
center cut of one ply is placed over the outside edge of the second ply. If
ties of 7.2 and be fabricated in accordance with 7.3. narrower width mat is used, reverse the second ply 180° in the machine
C581 − 20
direction and lay it on top of the first ply to minimize weight variations.
8. Procedure
7.3.3 Follow with a 10-mil (0.25-mm) surfacing mat as in
8.1 Measurement of Specimens—Immediately following the
7.3.1.
curing period, measure the thickness of the specimens to the
7.3.4 Remove the air by rolling over the surface with a
nearest 0.001 in. (0.025 mm) at the geometric center of each of
serrated metal or plastic roller. Take care not to expel enough
the intended 1 by 3 in. (25.4 by 76.2 mm) specimens that will
resin to raise the glass content above the permissible maxi-
becutforflexuraltestsafterthecompletedexposures.Measure
mum.The laminate is considered within the range of allowable
the weight of the specimens to the nearest 0.01 g. These
levels of resin and glass if the thickness of the laminate is
thickness and weight measurements shall also be used for
within 0.120 and 0.140 in. (3.05 and 3.56 mm), as described in
comparison against thickness and weight measurements after
7.2.2.
the completed exposures.
7.3.5 After the lay-up is completed, cover the laminate with
8.2 Exposure—Following the curing period, as specified in
a plastic release film to prevent air inhibition or to provide a
7.3.6,priortoimmersion,recordabriefdescriptionofthecolor
uniform smooth glossy surface, or both. Carefully smooth
and surface appearance of the coupons and the color and the
down to remove entrapped air.
clarity of the test solution. The total number of coupons per
container is not limited except by the ability of the container to
NOTE 5—It is acceptable to use any convenient method for the
application of the release film. Regardless of how it is applied, it is critical
hold the coupons without touching each other or the container.
that any entrapped air between the film and the laminate be entirely
The coupons must always be completely immersed. Coupons
removed. One method of application is done by previously wrappin
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C581 − 15 C581 − 20 An American National Standard
Standard Practice for
Determining Chemical Resistance of Thermosetting Resins
Used in Glass-Fiber-Reinforced Structures Intended for
Liquid Service
This standard is issued under the fixed designation C581; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope Scope*
1.1 This practice is designed to evaluate, in an unstressed state, the chemical resistance of thermosetting resins used in the
fabrication of reinforced thermosetting plastic (RTP) laminates. This practice provides for the determination of changes in the
properties, described as follows, of the test specimens and test reagent after exposure of the specimens to the reagent: hardness
of specimens, weight change thickness, appearance of specimens, appearance of immersion media, and flexural strength and
modulus.
1.1.1 This practice is also useful to evaluate other factors, such as surfacing veils and the effect of resin additives, on the
chemical resistance of the resin.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
NOTE 1—There is no known ISO equivalent to this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D790 Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
D883 Terminology Relating to Plastics
D2563 Practice for Classifying Visual Defects in Glass-Reinforced Plastic Laminate Parts
D2583 Test Method for Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor
D2584 Test Method for Ignition Loss of Cured Reinforced Resins
3. Terminology
3.1 Definitions of Terms:
3.1.1 For definitions of terms associated with plastic materials, see Terminology D883.
4. Significance and Use
4.1 The results obtained by this practice shall serve as a guide in, but not as the sole basis for, selection of a thermosetting resin
used in an RTP structure. No attempt has been made to incorporate into the practice all the various factors that will potentially affect
This practice is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.23 on Reinforced Plastic Piping Systems
and Chemical Equipment.
Current edition approved Dec. 1, 2015Feb. 15, 2020. Published January 2016March 2020. Originally approved in 1965. Last previous edition approved in 20082015 as
ɛ1
C581 – 03C581 – 15.(2008) . DOI: 10.1520/C0581-15.10.1520/C0581-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C581 − 20
the serviceability of an RTP structure when subjected to chemical environments. These factors will potentially include stress,
different resin-to-glass ratios, and multiple veils.
5. Apparatus
5.1 Hardness Testing Instrument—This shall be as described in Test Method D2583.
5.2 Flexural Properties Testing Apparatus, in accordance with Test Methods D790.
5.3 Thickness Measurement—A micrometer suitable for measurement to 0.001 in. (0.025 mm).
5.4 Containers, of sufficient size, capacity, and inertness to allow total immersion of reinforced thermosetting plastic specimens
in the specific corrosives chosen for testing. These containers shall, when necessary, be capable of maintaining liquid levels of
volatile solutions, that is, solvents. This can be accomplished by the use of reflux condensers.
5.5 Heating Apparatus—A constant temperature oven, heating mantle, or liquid bath capable of maintaining temperature within
range of 64.0°F (62.2°C). Take proper precautions if the corrosives selected are flammable liquids.
5.6 Analytical Balance, suitable for accurate weighing to 0.001 g.
6. Reagents
6.1 The test media shall consist of the reagents or solutions to which the RTP laminates are to be exposed.
7. Test Specimens
7.1 Standard Laminates—Prepare standard fiber-reinforced laminates using identical reinforcement in all of the laminates. The
laminates shall be constructed of the following materials:
7.1.1 Surfacing Mat (Veil)—A thin mat of fine fibers used primarily to produce a smooth, resin-rich surface on a reinforced
plastic. The surfacing veil helps determine the thickness of the resin-rich layer, reduces microcracking and provides a non-wicking
chemically–resistant layer. The surfacing veil shall be compatible with the resin,resin and manufactured with uniform fiber
distribution and non-bundled fibers. The dry veil layer(s) shall be a minimum 10 mils in thickness and produce a 10 to 15 mil
resin-saturated veil layer per 10 mils of dry veil. To eliminate the surfacing veil as a variable in corrosion tests, prepare each
laminate within a test group with the same surfacing veil.
7.1.2 Chopped Strand Mat—Type E glass fiber with sizing and binder compatible with the resin. It is acceptable to use other
glass fiber compositions, but using such alternate compositions shall be considered as variables for comparison to the standard.
7.1.2.1 Note that this practice applies to E-CR glass fiber, which is a type of E glass fiber. If the E glass fiber material is of the
E-CR type that information shall be identified in the test report.
7.1.3 Resin—Catalyzed and promoted in accordance with the resin manufacturer’s recommendation.
NOTE 2—It is acceptable to add fillers, such as antimony trioxide for improved fire performance or thixotropes for viscosity control, but it is possible
that this will detract from the corrosion resistance of the test laminate.
7.2 Dimensions and General Properties—The laminates shall conform to the required dimensions and general properties of 7.2
and be fabricated in accordance with 7.3.
7.2.1 Laminate Size—A suitable laminate size has been found to be 26 by 33 in. (660 by 838 mm) after trimming. This laminate
size is not restrictive and other dimensions are acceptable.
7.2.2 Thickness—The thickness of the cured standard laminate shall be between 0.120 and 0.140 in. (3.05 and 3.56 mm).
2 2
7.2.3 Reinforcement Content—The glass fiber and binder shall be 4.73 6 0.47 oz/ft (three layers of 1.5 oz/ft chopped strand
2 2
mat 4.5 oz/ft having a nominal binder content of 3.5 % and two layers of 10 mil surfacing mat 0.23 oz/ft having a nominal binder
content of 7 %)—determined by preweighingpre-weighing the materials prior to construction of the laminate. This is equivalent
to 23.6 weight % (12.5 volume %) glass fiber when using a resin having a cured specific gravity of 1.15. Such a laminate will have
a thickness of 0.125 in. (3.18 mm). The use of resins having different specific gravities will result in different weight percentages
of glass fiber, but the volume percentage of glass fiber will remain the same. When using synthetic organic fiber surfacing veil,
2 2
the glass content shall be 4.50 6 0.45 oz/ft ( three (three layers of 1.5oz/ft1.5 oz/ft chopped strand mat having a nominal binder
content of 3.5 %).
7.2.4 Hardness—The hardness shall be at least 90 % of that of a fully-cured clear casting of the resin, or of a similarly
constructed laminate as defined by the resin manufacturer. Hardness shall be determined in accordance with s5.1. Note that the use
of synthetic veil will result in significantly lower hardness values. The hardness value will vary with the type of resin and number
of plies of synthetic veil. The resin manufacturer needs to be contacted for the allowable Barcol hardness value of a laminate
containing synthetic veils with the specific resin.
7.2.5 Laminate Condition—The laminate shall meet Acceptance Level I of Table I of Practice D2563.
7.3 Fabrication of Standard Laminate—The sequence of lay-up shall be as follows:
7.3.1 Apply catalyzed resin and a 10-mil (0.25-mm) surfacing mat on a flat surface covered with plastic release film or treated
with a suitable release agent and roll to distribute resin.
NOTE 3—Use the following formula as a guide to determine the total weight of resin to be used. This is equivalent to 12.5 volume % glass fiber in
C581 − 20
the laminate. Grams resin equals grams glass fiber material per 7.2.3 times 2.82 G. Where G equals specific gravity of cured resin. It is acceptable to
use excess resin due to loss by adhering to mixing containers, rollers, and other factors. A suggested amount of excess resin is 10 to 15 % by weight.
7.3.2 Follow with three plies of 1.5 oz/ft chopped strand mat and resin. Roll after each ply to distribute and wet-out the chopped
strand mat. Rolling with a serrated roller is acceptable after each ply to remove entrapped air but it shall be done in accordance
with 7.3.4. The mat weight shall be within 65 % of 1.5 oz/ft upon weighing the full 26 by 33-in. cut (660 by 838-mm) piece,
(or other full dimension used, 7.2.1.).
NOTE 4—Cut chopped strand mat so that the 26-in. dimension is across the width of the roll and the 33-in. dimension is along the machine direction
of the mat. Mat weight variation will most commonly occur across the width of the mat. If a wide roll of mat, 52 in. (1320 mm) or greater, is used, place
the two plies of mat in the laminate such that the center cut of one ply is placed over the outside edge of the second ply. If narrower width mat is used,
reverse the second ply 180° in the machine direction and lay it on top of the first ply to minimize weight variations.
7.3.3 Follow with a 10-mil (0.25-mm) surfacing mat as in 7.3.1.
7.3.4 Remove the air by rolling over the surface with a serrated metal or plastic roller. Take care not to expel enough resin to
raise the glass content above the permissible maximum. The laminate is considered within the range of allowable levels of resin
and glass if the thickness of the laminate is within 0.120 and 0.140 in. (3.05 and 3.56 mm), as described in 7.2.2.
7.3.5 After the lay-up is completed, cover the laminate with a plastic release film to prevent air inhibition or to provide a uniform
smooth glossy surface, or both. Carefully smooth down to remove entrapped air.
NOTE 5—It is acceptable to use any convenient method for the application of the release film. Regardless of how it is applied, it is critical that any
entrapped air between the film and the laminate be entirely removed. One method of application is done by previously wrapping the film around a metal
rod. Starting at one edge of the laminate, slowly unroll the film from the rod, keeping a bead of resin ahead of the rod as you cross the laminate. Any
entrapped air remaining can be removed by rubbing a tongue depressor across the release film surface. Carefully pull the film taut and fasten at the edges
to prevent wrinkling of the film. Placing stops (neoprene has been found to be suitable) around the edges of the laminate and passing a heavy metal roller
over the laminate helps to insure uniform controlled thickness.
7.3.6 Cure as recommended by the resin manufacturer. The cure schedule shall be reported.
7.3.7 Trim edges as required.
7.4 Record of Standard Laminate Construction—Record the properties of the standard laminate as follows:
7.4.1 Hardness—Determine Barcol hardness on the strip as described in 7.2.4 in accordance with Test Method D25
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