ASTM D4688-99
(Test Method)Standard Test Method for Evaluating Structural Adhesives for Finger Jointing Lumber
Standard Test Method for Evaluating Structural Adhesives for Finger Jointing Lumber
SCOPE
1.1 These test methods cover the evaluation of adhesives for finger jointing lumber used in the manufacture of structural glued laminated timber. They include tests of the tensile strength of joints; dry with no treatment, wet after one vacuum-pressure soak treatment, and wet after cyclic boil-dry treatment.
1.2 The values stated in inch-pound units are to be regarded as the 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 4688 – 99
Standard Test Method for
Evaluating Structural Adhesives for Finger Jointing Lumber
This standard is issued under the fixed designation D 4688; 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 (e) indicates an editorial change since the last revision or reapproval.
1 3
1. Scope 3.2.4 specimen, n—an individual strip, ⁄4 by 1 ⁄8 (approxi-
mately)by12in.(6.4by35by305mm),cutfromafingerjoint
1.1 This test method is designed to evaluate adhesives for
assembly for the tension test described in this test method.
finger jointing lumber used in the manufacture of structural
glued laminated timber. It tests the tensile strength of joints
4. Significance and Use
under the following treatments; dry with no treatment, wet
4.1 This test method is specifically designed to measure the
after one vacuum-pressure soak treatment, and wet after cyclic
performance of adhesives in finger joints manufactured under
boil-dry treatment.
production line conditions.
1.2 The values stated in SI units are to be regarded as the
4.2 The results of the test method may be used to certify an
standard. The inch-pound units in parentheses are for informa-
adhesive as suitable for finger jointing lumber under
tion only.
production-line conditions where the intended end use of the
1.3 This standard does not purport to address all of the
finger jointed lumber will be in a structural glued laminated
safety concerns, if any, associated with its use. It is the
timber. When the test results are to be used for certification of
responsibility of the user of this standard to establish appro-
an adhesive for this purpose, use a standard wood species and
priate safety and health practices and determine the applica-
a standard finger profile. Standard species may be found in
bility of regulatory limitations prior to use.
Table 1 of Specification D 2559. Two standard finger profiles
2. Referenced Documents commonly used in the manufacture of structural glued lami-
nated timber industry are shown in Fig. 1.
2.1 ASTM Standards:
4.3 This test method is not intended for quality control as
D 907 Terminology of Adhesives
the test assemblies are selected for their absence of defects
D 2559 Specification for Adhesives for Structural Lami-
usually found in run-of-the-mill lumber and finger joints.
nated Wood Products for Use Under Exterior (Wet Use)
Exposure Conditions
5. Apparatus
3. Terminology 5.1 Test Machine, capable of applying a calibrated tensile
force up to 23 kN (5000 lbf), equipped with Templin (wedge-
3.1 Definitions—Many terms in this test method are defined
action) grips with grip area of 38 by 75 mm (1 ⁄2 by 3 in.).
in Terminology D 907.
5.2 Vacuum Pressure Vessel, capable of drawing and hold-
3.2 Definitions of Terms Specific to This Standard:
ing a vacuum of at least 635 mm (25 in.) of mercury (sea level)
3.2.1 billet, n—a piece cut from a vertical finger joint
for 30 min, holding a pressure of 620 6 35 kPa (75 6 2 psi)
assembly as an intermediate step in making specimens.
for 30 min, and capacity to ensure that all of the specimens are
3.2.2 finger joint assembly, n—ashortportionoftwoboards
at least 51 mm (2 in.) below the water level during the
joinedattheirendsbyafingerjointobtainedfromafingerjoint
complete vacuum-pressure cycle.
production line for testing, frequently referred to as an assem-
5.3 Tank for Boiling, capacity such that all specimens are at
bly.
least51mm(2in.)belowthewaterlevelforthedurationofthe
3.2.3 sample, n—agroupoffingerjointassembliesobtained
boil cycles.
from a finger joint production line for statistical purposes.
5.4 Oven, capable of operating continuously for 20 h at 63
3.2.3.1 Discussion—In the laminating industry the term
6 2°C (145 6 5°F) with sufficient air circulation to lower the
sample is used for an individual finger joint assembly.
moisture content of the group of specimens to 8 % within 20 h.
5.4.1 Timer, to shut the oven off automatically is desirable.
This test method is under the jurisdiction of ASTM Committee D-14 on
Adhesives and is the direct responsibility of Subcommittee D14.30 on Wood
Adhesives.
Current edition approved Oct. 10, 1999. Published December 1999. Originally
published as D 4688 – 87. Last previous edition D 4688 – 95 (1999). AmericanInstituteofTimberConstruction,7012S.RevereParkway,Suite140,
Annual Book of ASTM Standards, Vol 15.06. Englewood, CO 80112.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4688–99
FIG. 2 Finger Joint Assembly and Specimen Descriptions
6.2.4 Cut the assembly to a 305-mm (12-in.) length with the
finger jointed area at the center.
6.2.5 Rip individual specimens 6.4-mm ( ⁄4-in.) thick (Fig.
1) from the assembly starting with the jointed edge of the
assembly (see 6.2.2) against the saw guide. A thin hollow-
ground rip saw blade is preferred but the important criteria is
the straightness of the cut. Check cut specimens for uniform
thickness throughout. Thickness shall not vary by more than
0.5 mm (0.02 in.). Number the specimens in order from one
side of the assembly to the other.
6.3 Vertical Joint (Fig. 2(b)):
6.3.1 Joint one edge of the finger joint assembly.
6.3.2 Joint one face of the finger joint assembly.
NOTE 1—Recommended by American Institute of Timber Construc-
6.3.3 With the jointed edge against the saw guide, rip billets
tion.
40 mm (1 ⁄16 in.) wide from the assembly.
FIG. 1 Standard Joint Profiles for Certification Tests
NOTE 2—The 40-mm (1 ⁄16-in.) dimension is not critical but this
dimension must be enough to allow feathering the fingers in following
steps.
6. Specimen Preparation
6.3.4 Joint and plane the sides of each billet so the exposed
6.1 Obtain a sample consisting of either 20 horizontal or
sides of the fingers are feathered as described in 6.2.1 and
vertical finger joint assemblies from a finger joint production
6.2.3.
line.Theboardsmustbenominal2by4-in.or2by6-in.Reject
6.3.5 Rip four individual specimens of 6.4-mm ( ⁄4-in.)
any assembly with obvious defects in the lumber or joint.
thickness from each billet of the assembly as in 6.2.5. Number
6.2 Horizontal Joint (Fig. 2(a)):
the specimens in order from one side of the assembly to the
6.2.1 Joint one face of each assembly until the finger on the
other. Use the same order for each assembly.
surface is feathered as shown in Fig. 2(c).
6.4 Inspect specimens for defects. Assemblies yielding
6.2.2 Joint one edge of the assembly for end cutting and
specimens that have obvious strength-reducing characteristics
ripping at a later stage.
such as: low visual density, knots, steep slope of grain,
6.2.3 Plane the second face of the assembly until the finger
compression wood, compression failures, decay, pitch pockets,
on the surface is feathered maintaining 35-mm (1 ⁄8-in.)
or stress risers due to errors in specimen preparation, may be
assembly thickness or nearly so.
rejected. If specimens with questionable strength characteris-
tics are tested they shall be identified by appropriate notes on
NOTE 1—It is more important to feather the finger than to maintain the
35-mm (1 ⁄8-in.) thickness. the report form prior to exposure and testing.
D4688–99
to ensure proper front-to-rear alignment, and a plumb bob or other device
6.5 Condition all specimens to equilibrium moisture content
is recommended to ensure the vertical alignment.
(EMC) at 23 6 2°C (73 6 4°F) and 50 to 65 6 5 % relative
humidity. Monitor the weight periodically to determine when
7.1.2 Determine the failure mode using the criteria given in
equilibrium is reached.
Annex A1 independent of any knowledge of the strength test
6.6 Weigh all specimens to the nearest 0.01 g and record the
result.
weight. Measure the width and thickness of the specimens to
7.2 Cold Water Vacuum-Pressure Soak Test:
the nearest 0.25 mm (0.010 in.) and record the measurements.
7.2.1 As described in 6.7, assign 40 specimens to this test.
6.7 Randomly assign two specimens from each of the 20
Place all 40 specimens in a vacuum-pressure vessel with
finger joint assemblies in the sample to each test (that is, dry,
spacers between them so that water has free access to all
soak, and boil). (Note this requires only six specimens from
surfaces. Fill the vessel with tap water at 18.5 to 27.5°C (65 to
each assembly, the other specimens are extra.) Fig. 3 shows the
80°F) so that all specimens are at least 51 mm (2 in.) below the
source and distribution of the specimens.
surface of the water. After filling, seal the vessel and draw a
vacuum of at least 635 mm (25 in.) of mercury (sea level).
7. Procedure
Hold the vacuum for 30 min, then release the vacuum and
7.1 Dry Test (No Treatment):
apply pressure of 620 6 35 kPa (75 6 2 psi). Hold this
7.1.1 As described in 6.7, assign 40 specimens to this test.
pressure for 2 h, then release. Remove the specimens from the
Test each specimen to failure by loading at a rate of 5 mm/min
pressure vessel and place them submerged in water at room
(0.20 in./min). Maintain a space of 210 66mm(6 6 0.25 in.)
temperature until tested.
between the ends of the jaws of the grips. Record the load at
7.2.2 Wipe the surface of each specimen with a dry cotton
failure.
cloth or paper towel and test wet as described in 7.1.1. Record
the load at failure.
NOTE 3—Be very careful to align the specimen with the principal axis
7.2.3 After the specimens have dried, determine the failure
ofthetestgrip.Failuretodothiswillincreasethevariabilityoftheresults.
Markings or spacers on the grips, or some other device is recommended mode as described in 7.1.2. Record the failure mode.
NOTE 1—Thus: 20 assemblies 3 2 specimens/assembly = 40 specimens/test.
FIG. 3 Flowchart of the Source and Allocation of Individual Test Specimens
D4688–99
7.3 Cyclic Boil Test:
Upper adjacent value = the largest observation equal to or less than
the quantity Q3+1.5(Q3− Q1).
7.3.1 As described in 6.7, assign 40 specimens to this test.
Lower adjacent value = the smallest observation greater than or equal
Place all 40 specimens in the boil tank with spacers so that
to the quantity Q1−1.5(Q3− Q1).
water has free access to all surfaces. Fill with water such that Outliers = observations greater than the upper adjacent
value or less than the lower adjacent value.
the specimens are at least 51 mm (2 in.) below the water level.
Boil specimens for 4 h, then dry them in an oven at 63 6 2°C
8.4 Calculate the mean and standard deviation. Specimens
(145 65°F)withsufficientaircirculationtolowerthemoisture
exhibiting failure mode 6 may be excluded from the calcula-
content to 8 % (ovendry basis) in no more than 20 h.
tion. Include specimens with failure modes 1, 2, 3, 4, and 5 in
the calculation unless the strength value is an outlier or the
NOTE 4—The rate of air circulation, the size of the load of specimens
wood is of poor quality (such as compression wood, etc.).
in the oven, and the spacing of the specimens greatly affect drying time
and the steepness of the moisture gradient in the specimen. Variation of
9. Report
these factors strongly affects the repeatability of the test method. If
repeatability (within-laboratory variability) or reproducibility (between
9.1 Include the following general information in the report:
laboratories) is important, the drying variables must be maintained as
9.1.1 Complete identification of the adhesive tested includ-
constant as possible from one series of tests to the next. If this is not
ing type, source, manufacturers’ code numbers, form, and any
possible, the drying should be conducted so that the specimens reach 8 %
other pertinent information,
moisture content within the same drying period in every test. One way to
9.1.2 Adhesive application and bonding conditions used to
do this is to monitor the weight of the specimens and adjust the oven vents
prepare the finger jointed boards,
so the specimens reach the target 8 % moisture in 15 to 20 h.As an aid in
following moisture content, the weight of specimens at 8 % moisture 9.1.3 Conditioning procedure used before testing,
contentisabout96 %oftheirweightat12 %moisturecontent.Thedrying
9.1.4 Temperature and relative humidity of the test room,
time required can be established with some of the extra specimens cut
9.1.5 Number of finger joint assemblies represented in the
from the 20 assemblies.
test, and
7.3.2 Repeat the boil-dry cycle five more times; except
9.1.6 Number of specimens per assembly tested in each test
during the final cycle do not dry the specimens. Cool the
(dry, soaked, and boiled),
specimens to room temperature submerged in water and keep
9.2 Include the following statistical information in the
them there until they are tested.
report:
7.3.3 Test wet in tension as described in 7.2.2. Record the
9.2.1 The range of test values,
load at failure.
9.2.2 The 25th, 50th, and 75th percentile values,
7.3.4 After the specimens have dried, determine the failure
9.2.3 The upper and lower adjacent values,
mode as described in 7.1.2. Record the failure mode.
9.2.4 Outliers identified by finger joint assembly and speci-
men number,
NOTE 5—Nonmandatory guidelines for joint performance follow:
9.2.5 Failure mode 6 specimens identified by finger joint
Mode 1 — An unacceptable failure.
assembly and specimen number,
Modes 2 and 3 — Unconditionally acceptable failure.
Modes 4, 5, and 6 — Conditionally acceptable failure if strength is ac-
9.2.6 Specimens with defects of material or bonding discov-
ceptable.
ered after testing identified by finger joint assembly and
specimen number,
8. Calculation of Results
9.2.7 The mean and standard deviation, and
8.1 Calculate the tensile stress at failure in megapascals
9.2.8 The statistical mode (most frequent value) of the
(pounds-force per square inch) as the load at failure in newtons
observed failure modes.
(pounds-force) divided by the cross-sectional area of the
2 2
10. Precision and Bias
specimen expressed to the nearest mm (0.01 in. ).
8.2 Estimate the 25th, 50th, and 75th percentiles for the
10.1 Ameasure of the precision of this test method covering
group of specimens in the following manner:
all possible types of finger joints has not been determined. It is
8.2.1 Arrange the specimens in order of increasing strength.
unlikely that a precision statement could be determined to
8.2.2 Estimate the 25th percentile as the average of the 10th
cover all possible cases because many factors that affect
and 11th lowest strength values.
precision, such as wood species, finger geometry, cutting tool
8.2.3 Estimate the 50th
...
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