ASTM D4688/D4688M-14(2021)e1

Standard Test Method for Evaluating Structural Adhesives for Finger Jointing Lumber

SIGNIFICANCE AND USE
4.1 This test method is specifically designed to measure the performance of adhesives in finger joints manufactured under production line conditions.  
4.1.1 The test method can be adapted to evaluate the adhesive performance of laboratory produced finger joints using commercial finger joint cutting heads with finger joints produced following the adhesive manufacturers recommendations. The conditions under which the finger joints were produced, including any limitations, are to be reported in 9.1.2.2 (see Note 2).
Note 2: If laboratory prepared finger joints are to be produced, record details related to adhesive used, its preparation, application to the cut finger joint, appropriate bonding parameters and limitations in the production of the finger joint assemblies.  
4.2 The results of the test method may be used to certify an adhesive as suitable for finger jointing lumber under production line conditions where the intended end use of the finger jointed lumber may be in a variety of bonded structural wood products.  
4.2.1 When the test results are to be used for certification of an adhesive a standard wood species shall be used.
4.2.1.1 Standard species may be found in Table 1 of Specification D2559.
SCOPE
1.1 This test method is designed to evaluate adhesives for finger jointing lumber used in the manufacture of a variety of bonded structural wood products such as structural glued laminated timber. It tests the tensile strength of joints under the following treatments: dry with no treatment, wet after one vacuum-pressure soak treatment, and wet after cyclic boil-dry treatment.  
1.2 This test method is intended neither for quality control as the test assemblies are selected for the absence of defects usually found in run-of-the-mill finger joints nor as a substitute for in-plant qualification of end joints, including full-scale joint tests.
Note 1: This test method is specifically designed to evaluate adhesives for use in finger jointing lumber using small scale test specimens cut from carefully selected finger joint assemblies. In contrast, plant qualification and quality control require tests of full scale end joints selected randomly from production, designed to evaluate parameters beyond adhesive performance which affect the performance of the end use product.  
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.  
1.4 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.  
1.5 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-Apr-2021
• ICS: 83.180 - Adhesives
• Technical Committee: D14 - Adhesives
• Drafting Committee: D14.30 - Wood Adhesives

Relations

• Refers: ASTM D5266-13(2020) - Standard Practice for Estimating the Percentage of Wood Failure in Adhesive Bonded Joints
• Effective Date: 01-Apr-2020
• Refers: ASTM D2559-12a(2018) - Standard Specification for Adhesives for Bonded Structural Wood Products for Use Under Exterior Exposure Conditions
• Effective Date: 01-Aug-2018
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM D5266-13 - Standard Practice for Estimating the Percentage of Wood Failure in Adhesive Bonded Joints
• Effective Date: 01-May-2013
• Refers: ASTM D907-12a - Standard Terminology of Adhesives
• Effective Date: 01-Jul-2012
• Refers: ASTM D2559-12a - Standard Specification for Adhesives for Bonded Structural Wood Products for Use Under Exterior Exposure Conditions
• Effective Date: 01-Jun-2012
• Refers: ASTM D2559-12ae1 - Standard Specification for Adhesives for Bonded Structural Wood Products for Use Under Exterior Exposure Conditions
• Effective Date: 01-Jun-2012
• Refers: ASTM D907-12 - Standard Terminology of Adhesives
• Effective Date: 01-May-2012
• Refers: ASTM D907-11a - Standard Terminology of Adhesives
• Effective Date: 01-Dec-2011
• Refers: ASTM D907-11 - Standard Terminology of Adhesives
• Effective Date: 01-Jan-2011
• Refers: ASTM D2559-10a - Standard Specification for Adhesives for Bonded Structural Wood Products for Use Under Exterior Exposure Conditions
• Effective Date: 01-Sep-2010
• Refers: ASTM E4-10 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2010
• Refers: ASTM D2559-10 - Standard Specification for Adhesives for Structural Laminated Wood Products for Use Under Exterior (Wet Use) Exposure Conditions
• Effective Date: 01-May-2010
• Refers: ASTM D2559-09 - Standard Specification for Adhesives for Structural Laminated Wood Products for Use Under Exterior (Wet Use) Exposure Conditions
• Effective Date: 01-Nov-2009
• Refers: ASTM E4-09a - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Nov-2009

Overview

ASTM D4688/D4688M-14(2021)e1 is the globally recognized standard test method developed by ASTM International for evaluating the performance of structural adhesives used in finger jointing lumber. This test method is specifically designed to simulate production line conditions, ensuring that adhesives used in construction and manufacturing are suitable for bonding lumber for structural wood products such as glued laminated timber. By employing standardized procedures, the method provides a consistent approach to determining the tensile strength of finger joints after exposure to various conditioning treatments.

The standard is essential for manufacturers, quality assurance professionals, and certifying agencies looking to assess or certify the performance and durability of structural wood adhesives under real-world and laboratory-prepared conditions.

Key Topics

• Structural Adhesive Performance
  The standard focuses on evaluating adhesives under production-like conditions to ensure robust bonding in finger-jointed lumber.

• Test Treatments
  Adhesive bond strength is tested under three conditions:

  • Dry (no treatment)
  • Wet after vacuum-pressure soak
  • Wet after cyclic boil-dry treatment

• Specimen Preparation
  Finger jointed specimens are prepared from either production lines or laboratory setups using commercial finger joint cutting tools. Key variables, such as wood species, adhesive type, and bonding parameters, must be thoroughly documented.

• Certification Criteria
  Results from this method may be used to certify adhesives for use in finger jointed lumber, especially when a standard wood species is utilized as specified in ASTM D2559.

• Reporting and Analysis
  Detailed reporting is required, including adhesive and wood identification, bonding conditions, conditioning, test environments, and statistical results (such as percentile values, mean, standard deviation, and failure modes).

• Units and Precision
  Results must be reported in either SI or inch-pound units, but not a combination. The method emphasizes careful monitoring of variables affecting precision, such as wood species and joint geometry.

Applications

ASTM D4688/D4688M-14(2021)e1 is extensively applied in:

• Certification of Adhesives

  • Qualifying adhesives for use in structural wood products by verifying their performance under simulated service conditions.
  • Providing data for regulatory compliance and certification bodies regarding adhesive suitability.

• Quality Assurance and R&D

  • Assisting manufacturers in evaluating new or current adhesive formulations for finger jointing in production environments.
  • Serving as a reference for laboratory comparison and benchmarking performance across adhesive products.

• Construction and Manufacturing

  • Ensuring that finger jointed lumber used in structures like beams, headers, and laminated timber assemblies meets rigorous bonding standards.

• Technical Communication

  • Enabling clear, consistent reporting and comparison of adhesive performance across different laboratories and production settings.

Related Standards

• ASTM D907: Terminology of Adhesives
  Provides critical definitions used in adhesive technology and testing.

• ASTM D2559: Specification for Adhesives for Bonded Structural Wood Products for Use Under Exterior Exposure Conditions
  Specifies requirements for adhesives subjected to exterior exposure, referenced for wood species selection.

• ASTM D5266: Practice for Estimating the Percentage of Wood Failure in Adhesive Bonded Joints
  Details procedures to evaluate wood failure, integral to analysis in this standard.

• ASTM E4: Practices for Force Verification of Testing Machines
  Outlines requirements for test machine accuracy, essential for tensile strength determination.

Conclusion

ASTM D4688/D4688M-14(2021)e1 is a cornerstone standard for ensuring the performance and reliability of structural adhesives used in finger jointing lumber. It offers a thorough, reproducible method for stakeholders aiming to certify, compare, or improve adhesive products in the engineered wood products industry. Applying this standard contributes to safer, more durable, and high-quality wood structures in construction and manufacturing worldwide.

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.
´1
Designation: D4688/D4688M − 14 (Reapproved 2021)
Standard Test Method for
Evaluating Structural Adhesives for Finger Jointing Lumber
This standard is issued under the fixed designation D4688/D4688M; 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.
ε NOTE—An editorial correction was made in 6.5 in April 2021.
1. Scope 2. Referenced Documents
1.1 This test method is designed to evaluate adhesives for 2.1 ASTM Standards:
D907Terminology of Adhesives
finger jointing lumber used in the manufacture of a variety of
bonded structural wood products such as structural glued D2559Specification for Adhesives for Bonded Structural
Wood Products for Use Under Exterior Exposure Condi-
laminatedtimber.Itteststhetensilestrengthofjointsunderthe
following treatments: dry with no treatment, wet after one tions
D5266Practice for Estimating the Percentage of Wood
vacuum-pressure soak treatment, and wet after cyclic boil-dry
treatment. Failure in Adhesive Bonded Joints
E4Practices for Force Verification of Testing Machines
1.2 This test method is intended neither for quality control
as the test assemblies are selected for the absence of defects
3. Terminology
usuallyfoundinrun-of-the-millfingerjointsnorasasubstitute
3.1 Definitions—Many terms in this test method are defined
forin-plantqualificationofendjoints,includingfull-scalejoint
in Terminology D907.
tests.
3.2 Definitions of Terms Specific to This Standard:
NOTE1—Thistestmethodisspecificallydesignedtoevaluateadhesives
foruseinfingerjointinglumberusingsmallscaletestspecimenscutfrom 3.2.1 billet, n—a piece cut from a vertical finger joint
carefully selected finger joint assemblies. In contrast, plant qualification
assembly as an intermediate step in making specimens.
and quality control require tests of full scale end joints selected randomly
3.2.2 horizontal finger joint, n—a joint formed by bonding
from production, designed to evaluate parameters beyond adhesive
two precut members shaped like fingers where the profile is
performance which affect the performance of the end use product.
visible on the edge of the lumber (see Fig. 1(a)).
1.3 The values stated in either SI units or inch-pound units
3.2.3 vertical finger joint, n—ajointformedbybondingtwo
are to be regarded separately as standard. The values stated in
precut members shaped like fingers where the profile is on the
each system are not necessarily exact equivalents; therefore, to
wide face of the lumber (see Fig. 1(b)).
ensure conformance with the standard, each system shall be
used independently of the other, and values from the two
3.2.4 finger joint assembly, n—ashortportionoftwoboards
systems shall not be combined.
joined at their ends by an adhesively bonded finger joint to
create a longer piece, frequently referred to as an assembly.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.2.5 sample, n—agroupoffingerjointassembliesobtained
responsibility of the user of this standard to establish appro- fromafingerjointproductionlineorlaboratorypreparedfinger
priate safety, health, and environmental practices and deter- joints selected for statistical purposes.
mine the applicability of regulatory limitations prior to use.
3.2.6 specimen, n—an individual test piece prepared to
1.5 This international standard was developed in accor-
specific dimensions for the purpose of determining the adhe-
dance with internationally recognized principles on standard-
siveperformanceinaccordancewiththetensiontestsdescribed
ization established in the Decision on Principles for the
in this test method.
Development of International Standards, Guides and Recom-
4. Significance and Use
mendations issued by the World Trade Organization Technical
4.1 This test method is specifically designed to measure the
Barriers to Trade (TBT) Committee.
performance of adhesives in finger joints manufactured under
production line conditions.
This test method is under the jurisdiction of ASTM Committee D14 on
Adhesives and is the direct responsibility of Subcommittee D14.30 on Wood
Adhesives. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 15, 2021. Published April 2021. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1987. Last previous edition approved in 2014 as D4688/D4688M–14. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D4688_D4688M-14R21E01. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D4688/D4688M − 14 (2021)
5.3 Tank for Boiling, capacity such that all specimens are at
least51mm[2in.]belowthewaterlevelforthedurationofthe
boil cycles.
5.4 Oven, capable of operating continuously for 20 h at 63
6 2°C [145 6 5°F] with sufficient air circulation to lower the
moisture content of the group of specimens from saturation to
no more than 8% within 20 h.
5.4.1 Timer, to shut the oven off automatically is desirable.
6. Specimen Preparation
6.1 Obtain a sample consisting of either 20 horizontal or
vertical finger joint assemblies from a finger joint production
lineor,whenevaluatinglaboratorypreparedfingerjoints,from
a population of laboratory prepared finger joints. The boards
must be nominal 2 by 4-in. or 2 by 6-in.
6.1.1 Identify and record the wood species, joint
configuration, average specific gravity and moisture content.
6.2 Horizontal Joint (Fig. 1(a)):
6.2.1 Joint one face of each assembly until the finger on the
surface is feathered as shown in Fig. 1(c).
NOTE 3—In the context of this test method, feathering is described as a
FIG. 1 Finger Joint Assembly and Specimen Descriptions
process where the surface containing the respective vertical or horizontal
joint is planed to approximately center of the visible edge of the joint (see
Fig. 1(c)).
4.1.1 The test method can be adapted to evaluate the
6.2.2 Joint one edge of the assembly for end cutting and
adhesive performance of laboratory produced finger joints
ripping at a later stage.
using commercial finger joint cutting heads with finger joints
6.2.3 Plane the second face of the assembly until the finger
produced following the adhesive manufacturers recommenda-
on the surface is feathered while maintaining an assembly
tions. The conditions under which the finger joints were
thickness of about 35-mm [1 ⁄8-in.].
produced, including any limitations, are to be reported in
9.1.2.2 (see Note 2).
NOTE 4—It is more important to feather the finger than to maintain the
35-mm [1 ⁄8-in.] thickness.
NOTE 2—If laboratory prepared finger joints are to be produced, record
details related to adhesive used, its preparation, application to the cut 6.2.4 Cuttheassemblytoa305-mm[12-in.]lengthwiththe
finger joint, appropriate bonding parameters and limitations in the
finger joint at the center.
production of the finger joint assemblies.
6.2.5 Rip individual specimens 6.4-mm [ ⁄4-in.] thick from
4.2 The results of the test method may be used to certify an
theassemblystartingwiththejointededgeoftheassembly(see
adhesive as suitable for finger jointing lumber under produc-
6.2.2) against the saw guide. A thin hollow-ground rip saw
tion line conditions where the intended end use of the finger
blade is preferred but the important criterion is the straightness
jointed lumber may be in a variety of bonded structural wood
of the cut.
products.
6.2.5.1 Checkcutspecimensforuniformthicknessthrough-
4.2.1 When the test results are to be used for certification of
out. Thickness shall not vary by more than 0.5 mm [0.02 in.].
an adhesive a standard wood species shall be used.
6.2.5.2 Number the specimens in order from one side of the
4.2.1.1 Standard species may be found in Table 1 of
assembly to the other.
Specification D2559.
6.3 Vertical Joint (Fig. 1(b)):
5. Apparatus 6.3.1 Joint one edge of the finger joint assembly.
6.3.2 Joint one face of the finger joint assembly.
5.1 Test Machine, capable of applying a tensile force, up to
6.3.3 Withthejointededgeagainstthesawguide,ripbillets
23kN[5000lbf],havinganaccuracyof 61%whencalibrated
40 mm [1 ⁄16 in.] wide from the assembly.
in accordance with Practice E4, and equipped with Templin
(wedge-action) grips with grip area of 38 by 75 mm [1 ⁄2 by 3
NOTE 5—The 40-mm [1 ⁄16-in.] dimension is not critical but this
in.].
dimension must be enough to allow feathering the fingers in subsequent
steps.
5.2 Vacuum Pressure Vessel, capable of drawing and hold-
6.3.4 Joint and plane the sides of each billet so the exposed
ingavacuumofatleast635mm[25in.]ofmercury(sealevel)
sides of the fingers are feathered as described in 6.2.1 and
for 30 min, holding a pressure of 620 6 35 kPa [75 6 2 psi]
6.2.3.
for 30 min, and capacity to ensure that all of the specimens are
at least 50 mm [2 in.] below the water level during the 6.3.5 Rip four individual specimens of 6.4-mm [ ⁄4-in.]
complete vacuum-pressure cycle. thickness from each billet of the assembly as in 6.2.5.
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D4688/D4688M − 14 (2021)
6.3.5.1 Number the specimens in order from one side of the 7. Procedure
assembly to the other. Use the same order for each assembly.
7.1 Dry Test (No Treatment):
6.4 Inspect specimens for defects. Assemblies yielding
7.1.1 As described in 6.7, assign 40 specimens to this test.
specimens that have obvious strength-reducing characteristics
Test each specimen in tension to failure by loading at a rate of
such as: low visual density, knots, steep slope of grain,
5 mm/min [0.20 in./min]. Maintain a space of 155 66mm[6
compression wood, compression failures, decay, pitch pockets,
6 0.25 in.] between the ends of the jaws of the grips. Record
or stress risers due to errors in specimen preparation shall be
the load at failure.
rejected.
NOTE 7—Be very careful to align the specimen with the principal axis
6.5 Conditionallspecimenstoequilibriummoisturecontent
ofthetestgrip.Failuretodothiswillincreasethevariabilityoftheresults.
(EMC) at 20 6 2°C [68 6 3°F] and 65 6 5% relative
Markings, spacers on the grips, or some other device is recommended to
humidity. Monitor the weight of randomly selected specimens ensure proper front-to-rear alignment, and a plumb bob or other device is
recommended to ensure the vertical alignment.
periodically to determine when equilibrium is reached.
7.1.2 Determine and record the percentage of wood failure
6.6 Weighallspecimenstothenearest0.01gandrecordthe
weight. Measure the width and thickness of the specimens to and the failure mode using the criteria given in Annex A1
independent of any knowledge of the strength test result.
the nearest 0.25 mm [0.010 in.] and record the measurements.
6.7 Randomly assign two specimens from each of the 20
7.2 Cold Water Vacuum-Pressure Soak Test:
finger joint assemblies in the sample to each test (that is, dry,
7.2.1 As described in 6.7, assign 40 specimens to this test.
soak, and boil). (Note this requires only six specimens from
Place specimens in a vacuum-pressure vessel with spacers
eachassembly,theotherspecimensareextra.)Fig.2showsthe
between them so that water has free access to all surfaces. Fill
source and distribution of the specimens.
the vessel with tap water at 18.5 to 27.5°C [65 to 80°F] so that
allspecimensareatleast51mm[2in.]belowthesurfaceofthe
NOTE6—Thus:20assemblies×2specimens/assembly=40specimens/
test. water. After filling, seal the vessel and draw a vacuum of at
FIG. 2 Flowchart of the Source and Allocation of Individual Test Specimens
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D4688/D4688M − 14 (2021)
least 635 mm [25 in.] of mercury (sea level). Hold the vacuum 8.2.3 Estimate the 50th percentile as the average of the 20th
for 30 min, then release the vacuum and apply pressure of 620 and 21st values.
635kPa[75 62psi].Holdthispressurefor2h,thenrelease.
8.2.4 Estimate the 75th percentile as the average of the 30th
Removethespecimensfromthepressurevesselandplacethem and 31st strength values.
submerged in water at room temperature. Remove the speci-
8.3 Determine the upper and lower adjacent values (see
mens individually from the water, and test while wet within
definition below) for the group of specimens. Determine the
1h.
outliers (test values outside the range expressed by the upper
7.2.2 Test wet in tension as described in 7.1.1. Record the
and lower adjacent values).
load at failure.
25th percentile = Q1 = the value below which 25 % of the
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