DUPAHLITY OF RESORCINOL GLUE 130NDS
IN GUSSET-TYPE ASSEMIBLY JOINTS
SIMILAR TO THOSE USED IN
WOOD COATS
May 1948
INFORMATION' REVIEWED
AND REAFFIRMED
March 1956
No. 121714
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison 5, Wisconsin
In Cooperation with the University of Wisconsin
DURABILITY OF RESORCINOL GLUE BONDS IN GUSSET-TYPE
ASSEMBLY JOINTS SIMILAR TO MOSE USED IN WOOD BOATS]:
By M. L. SEW, Chemical Engineer
Summary
Plywood gusset-type assembly joints, similar to those used in V-bottom
boats for joining framing members, were glued with resorcinol, urea, and
casein glues at temperatures ranging from 40° to 60° F. and tested by exposures to severe moisture conditions. The results indicated that the durability of resorcinol glues was superior to that of casein and urea-resin glues.
With resorcinol-resin glues durable bonds were obtained at curing temperatures
as low as 4o° F. in assembly joints involving such combinations as mahogany
lumber and Douglas-fir plywood and spruce lumber and Douglas-fir plywood, and
at curing temperatures of 70° F. or higher, when white oak lumber and Douglasfir plywood were used. Some resorcinol glues, however, produced durable bonds
at 60° F. with the combinations involving oak.
A joint employing a single gusset appeared to be a less satisfactory
construction than a double-gusset type under severe exposure conditions; and
even with the double-gusset type protection from rapid moisture changes
appeared to be desirable with combinations involving flat-grain white oak and
Douglas-fir plywood.
Specimens were fabricated using either bolts or clamps to supply gluing
pressure. Adequate bonds were obtained with both methods. Omission of bolts
would appreciably reduce weight in constructions where a large number of
bolted gussets are employed.
Introduction
Plywood gussets are widely used in small wood boats for joinins various
structural members. They are fastened by screws or bolts, which are often
supplemented by glue between the mating surfaces. Urea resin and, to a lesser
extent, casein glues have been used for this purpose. Urea resin provides
considerable water resistance, and when the temperature is-70° F. or higher,
at which urea resin cures satisfactorily, it may be used in the assembly of
boat parts on the ways. Casein glue has less water resistance than urea
1
'This study was made in cooperation with the Bureau of Ships, U. S. Navy.
Report No. R1714
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resins, but when low temperatures prevail at the assembly operation, casein
glue is nevertheless often used, since it cures at the lower temperatures.
Neither glue, however, is highly durable when subjected, to extreme moisture
and heat, as is often the case for wood boats in service.
The excellent • .durability provided by resorcinol glues under severe
exposures has recently directed attention to their use in boat-assembly
operations. It is known that they cure adequately for many purposes at
temperatures as low as 70° F., although they require a higher temperature
when used for laminating white oak ship timbers. A temperature of 70° F. is
higher than that often prevailing in boatbuilding plants, which are often
open buildings. There was need, therefore, to study the ability of resorcinol
resin to provide durable joints when used to glue plywood gusset-plate
assembly joints in boats, and to study further the minimum temperatures at
which such glues would cure adequately when used in such joints.
Results of earlier testa 2– showed that resorcinol glues developed appreciable dry and wet strength with extended curing at temperatures below 80° F.,
which indicated that even when cured at 40° F., they might be satisfactory for
gluing certain species of wood.
The purpose of this study was to investigate the suitability of
resorcinol adhesives for boat-assembly gluing, when used and cured at temperatures ranging from 40° to 80° F. The study consisted of preparing glued
gusset-type joints, exposing them by various accelerated tests to extreme
moisture conditions, and observing their resistance to glue-joint delamination. The study did not include mechanical tests on the strength of the glue
joints,
Materials and Procedures
Glues
Studies on the laminating of white oak have shown that resorcinol glues
do not all perform equally well. For this reason, three different commercial
resorcinol glues were used. One casein and one urea-resin glue were included
for comparison. They are designated in this report by letter symbols as
follows:
A - Resorcinol resin; formaldehyde hardener
B - Resorcinol resin; paraformaldehyde hardener
C - Resorcinol resin; paraformaldehyde hardener
D - Urea resin; catalyst included
E - Casein glue (containing preservative).
Olson, W. Z., Bruce, H. D., and Soper, V. R. "Curing of Resorcinol-resin
Glues at Temperatures from 40° to 80° F." Forest Products Laboratory
Report No. 81629, September 1946.
Report No. R1714
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Species and Types of Specimens
The types of specimens used in this study simulated the joints between
floor and top frame members at the chine in 17-bottom boats. The frame members
in such boats are usually made of lumber, joined at the chine and at the keel
with plywood gussets. The included angle at the chine between such frame
members usually ranges from 90 to 135 degrees or more. A 90-degree angle
between frame members was used in this study, and the angle between the grain
of the wood in the face ply of the gussets and the grain in the frame members
was 45 degrees. A sketch indicating the construction of the specimens used
in the major portion of the study is shown in figure 1(A). This illustrates
a type of joint made with two gussets. Figure 1(B) illustrates a joint made
with a single gusset. A few specimens of the latter type were used in this
study,
In the construction of the double-gusset type of joint (fig. 1(A)),
sanded exterior-type 3/8-inch three-ply Douglas-fir plywood was used for
gussets, and Sitka spruce, mahogany, and white oak lumber finished to 3/4 inch
was used for the frame members.
For the single-gusset joints (fig. 1(B)), sanded 3/4-inch five-ply
Douglas-fir plywood of exterior type was used for gussets and 3/4-inch white
oak, mahogany, and Sitka spruce for frame members, The lumber for the frames
was generally flat grain in both types of specimen.
Methods of Assembling
In accordance with common practice in assembling the types of joints
previously described, carriage bolts were used to join the parts and to supply
the gluing pressure on most specimens. A number of specimens on which clamp
pressure, but no bolts, was used, were also included for comparison. Bolt
spacings used for the double-gusset joints are shown in figure 1(A) and for
the single-gusset joints in figure 1(B). Some exploratory work was done to
find a suitable bolt spacing for applying gluing pressure, and in the specimens used for this purpose the bolts were removed and the joints were broken
apart while dry to determine the initial quality of the glue bond. Two of the
patterns tried are shown in figure 2(A) and (B). The pattern (or spacing)
involving the least number of bolts and still producing glue bonds that
appeared to be uniformly adequate, is shown in figure 1(A), and this spacing
was used in making the bolted double-gusset specimens. One-quarter-inch
carriage bolts were used for both types of joints.
Gluing Procedure
The following gluing procedures were used with each type of glue:
1. Resorcinol-resin glue
(a) Glue-s-oread -- about 60 pounds per 1,000 square feet of
joint area applied by double spreading (both contacting
surfaces of a joint coated with glue).
Report No. R1714
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(b) Closed assembly time -- 10 to 15 minutes, the longer
assembly times being used at the lower temperatures.
(c) Curing temperatures -- 40°, 50°, 60 0 , 7C °, and 80° F.,
maintained for 2 weeks. (It is realized that a shorter
pressing and curing period would have been adequate at
the higher curing temperatures, but for the sake of
uniformity the same pressing time was used throughout
the entire curing range.)
2. Urea-resin glue
(a) Glue spread -- about 50 pounds per 1,000 square feet
of joint area, applied by double spreading.
(b) Closed assembly time -- about 5 minutes.
(c) Curing temperatures -- 50°, 60°, 70°, and 80° F.
3. Casein glue
(a) Glue spread -- about 75 pounds per 1,000 square feet
of joint area, applied by double spreading.
(b) Closed assembly time -- about 5 minutes.
(c) Curing temperatures -- 50°, 60°, 70°, and 80° F.
The gluing was done in rooms maintained at the respective curing
temperatures being studied; and at the lower room temperatures (40° and 50° F.),
the glues were maintained at about 75° F. on a sand bath to keep them at a
spreadable consistency.
As soon as the glue had been applied to the wood surfaces, the joints
were assembled without pressure. At the expiration of the indicated closedassembly period, the bolts were drawn tight and the assembly set aside for
curing.
Testing Procedures
After a 2-week curing period, the pressure was released (bolts and
clamps removed) from all specimens except those made with casein glue. The
glue squeeze-out was then removed, and the edges of the specimens lightly
jointed to produce clean surfaces that would facili rete meastr. Ing de'tamination in subsequent exposures. For the specimens made with casein glue the
bolts were left in place.
The testing consisted of subjecting different groups of specimens to
three different types of cyclic exposures during which measurements were made
of the amount of delamination or separation that developed in the assembly
joints.
Report No. R1714
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At the completion of the cyclic tests, all specimens that still
appeared to be in satisfactory condition were put on outdoor racks for a
weathering test. The amount of delamination in each specimen:was again
measured after a 10-month weathering period.
The exposure cycles were carried out as follows:
Exposure I -- Accelerated fresh-water soaking-and-drying cycle.--The
specimens were placed in an autoclave and immersed in cold fresh water. A
vacuum of 20 to 25 inches was then drawn and held for 2 hours. The vacuum
was broken, and 75 pounds of air pressure per square inch was applied and
held for 2 hours. The vacuum-pressure cycle was repeated once, with the
specimens remaining immersed, after which soaking was continued for 1 week
at atmospheric pressure in a room held at 60° F, The specimens were then
dried for 3 weeks at 60° F. and 50 percent or less relative humidity with
brisk circulation of air. The entire cycle was repeated twice for a total
test period of 3 months.
This was followed by three similar cycles, except that the drying was
carried out at 80° F. and 30 percent relative humidity and the soaking at
ordinary room temperature.
The reason for using the lower temperature in the first part of the
test was to avoid whatever additional curing might occur if the testing were
carried out at a higher temperature. During the first 3 months of testing,
the specimens were not exposed to temperatures above 60° F, except for the
short period required for jointing the edges in the woodworking shop.
During that part of the drying period in each cycle when open glue
joints were most in evidence, the delaminated areas were measured by means
of a feeler gage, and the amount of wood failure in the open joints was
also estimated.
The results after six cycles (6 months) of exposure are shown in
tables 1, 2, and 3.
Exposure II -- Salt-water soaking-and-drying cycle.--The specimens
were soaked for 1 month in salt water (4 percent) at 60° F. and then dried
for 1 month at 60° F. and 50 percent or less relative humidity with brisk
circulation of air. The cycle was repeated twice for a total test period of
6 months. During the last 3 months, it was not feasible to maintain low
humidity and the temperature of 60° F., so ordinary room conditions were used.
The method of measuring delamination of joints was similar to that used in
exposure I. Results after three cycles (6 months) are shown in tables 1, 2,
and 3.
Exposure III -- High-temperature, low-humidity and room-temperature,
high-humidity cycle.--The specimens were exposed for2 weeks at 158° F. and
20 percent relative humidity followed by 2 weeks at 80° F. and 97 percent
relative humidity. This cycle was repeated through a total test period of
Report No. R1714
6 months. The measuring and recording of open-joint areas were similar to
the method used for exposures I and II. Results are shown in tables 1, 2,
and 3.
Weathering Exposure
After completion of the cyclic tests, all specimens except those made
with casein glue and some of those made with urea resin were put on outdoor
weathering racks. They were examined for glue-joint delamination after
about 10 months' exposure.
Paint Protection
Boats are usually well-protected by paint that will retard moisture
changes. Since this study was concerned mainly with the durability of the
glue bonds under severe exposures, the majority of the specimens were
exposed unpainted; but for comparison, a few specimens were given two coats
of aluminum paint prior to testing.
Discussion of Results
The results of the three different cyclic exposure tests based upon
measurements and observations after a 6-month exposure period are shown in
tables 1, 2, and 3. In figures 3 to 12 photographs of various groups of
specimens show their condition after completion of the cyclic tests.
Urea-resin Glue Joints
Figure 3 shows double-gusset specimens with frame members of oak,
mahogany, and Sitka spruce, glued with urea resin and cured at 60° and 70° F.
These specimens were photographed after completing exposure I, and the values
for the amount of delamination developed are given in tables 1, 2, and 3.
The most severe glue-joint failure developed in joints made with oak
frames. About half and sometimes more of the assembly-joint area glued with
urea glue opened in exposure I in specimens cured at 60°, 70°, and 80° F.
Similar joints showed much better performance in exposure II (cycles of saltwater soaking and drying), but showed failure again in exposure III (cycles
involving heat and moisture).
Urea-glue joints in specimens having mahogany frames performed better
than those made with oak, but showed 10 percent delamination in exposure I
when cured at 70° Fq, and greater amounts when cured at the lower temperatures. Exposures II and III developed little or no delamination.
Report No. R1714
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Urea-glue joints performed best when spruce frames were used, and
showed little or no delamination in any of the tests when cured at 70°; but
they developed 11 percent delamination in exposure I when cured at 60° F.,
and failed completely in exposure I when cured at 50° E.
Casein-glued Joints
Double-gusset joints made with oak, mahogany, and Sitka spruce frame
members and glued with casein containing preservative are shown in figure 4
after completion of exposure I. The amount of delamination is shown in
tables 1, 2, and 3.
In general, casein-glued joints developed moderate to high delamination whenever soaking exposures were involved, even though the bolts were
left in place during the test. Because of the bolts, delamination was
retarded and the lack of durability of the glue joint was not fully revealed.
Painting specimens having oak frames with two coats of aluminum paint failed
to protect the casein-glued joints from delamination. No painted specimens
with mahogany or with spruce frames were included in the tests.
Resorcinol-glued Joints
White oak frame members.--Double-gusset specimens made with white oak
frames, glued With adhesive A cured at 40°, 50°, 60°, 70°, and 80° F. and
then tested by exposure I, are shown in figure 5. The specimen glued at
50° F. developed 10 percent of glue-joint delamination, and a slight amount
of delamination developed in specimens cured at other temperatures (table 1).
One specimen glued at 80° F. developed slight failure in the wood adjacent
to the glue line. In general, joints made with adhesive A performed satisfactorily in all tests throughout the entire curing-temperature range
(40 0 to 80° F.).
Similar specimens glued with adhesive B are shown in figure 6 as they
appeared at the end of exposure I. Slight delamination developed in the
specimens glued at 80° F., and the amount of glue-joint delamination in the
specimens cured at 70° and lower was probably greater than desirable for use
in boats. The joints cured at 70° F. and lower, however, were much superior
to any of the urea- and casein-glued oak-frame joints subjected to the same
test. Some specimens developed failure in the wood adjacent to the assembly
glue joints.
Figure 7 shows double-gusset assembly joints where the Douglas-fir
plywood had been glued to the white oak frames with adhesive C and then subjected to exposure I. Specimens glued at 40°, 70°, and 80° F. showed slight,
if any, delamination in exposure I, but showed 5 percent of glue-joint
delamination when cured at 60°, and 23 percent when cured at 50° F. (table 1).
Except for the results at 40°, the higher curing temperatures appeared more
effective than the lower, These joints also developed some rupture in the
wood. Their performance was much superior to that of urea- or casein-glued
oak assembly joints subjected to the same test.
Report No. 81714
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It general, exposures II and III developed much less delamination in
the resorcinol-glue joints than exposure I; and only in one case (glue B cured
at 50° F.) was there as much as 10 percent glue-joint delamination in exposure
II, and in exposure III the maximum separation of glue joints was 3 percent
(glue B cured at 80° F.). Any combinations of glue and curing temperature
showing good performance in exposure I were found to be equally satisfactory
when exposures II and III were used.
Mahogany frame members.--Delamination values in the glue joints after
testing of specimens made with mahogany frame members are shown in table 2.
In general, the assembly joints performed satisfactorily in all tests
with all three resorcinol glues cured at temperatures within the range of 40°
to 80° F., except for adhesive B, which, at a 60° F. curing temperature,
showed a degree'of delamination considered objectionable in exposure I with
specimens glued by both bolt and clamp pressure. Similar joints, however,
glued at 50° and 40° F. performed excellently in the same test.
A few specimens showed failure in the wood adjacent to the assembly
joint, although the glue joint was intact. This failure was the result of
stresses developed during the test in the assembly type of construction. It
seemed unlikely that such wood failure could be reduced by improvement in the
quality of the glue bond in the assembly joint.
Double-gusset specimens made with mahogany frame members and glued
with adhesive A are shown in figure 8.
Sitka spruce frame members.--Glue-joint-delamination values after test
ing in specimens made with Sitka spruce frame members are shown in table 3.
Within the limits of the experiment, all joints made with spruce frame members
and glued with resorcinol resins developed practically no glue failure. Joints
glued under bolt pressure performed equally well with those glued under clamp
pressure.
Double-gusset specimens made with Sitka spruce frame members and glued
with adhesive B are shown in figure 9.
Effect of Paint Protection
In figure 10 photographs are shown of specimens, glued and cured at
80° F., that were given two coats of aluminum paint prior to exposure
(exposure I). Observed data on delamination for painted specimens are shown
at the bottom of table 1. The effect of paint protection on the glue bonds in
severe exposures appeared to be only slight. The specimens glued with
resorcinols all appeared in good condition, while those glued with urea and
casein showed practically the same amount of delamination as the unpainted
specimens made with these glues at 70° F.
Report No. R1714
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Effect of Construction
Photographs of single-gusset specimens are shown in figures 11 and 12
(all previous figures have illustrated joints of the double-gusset types).
Delamination values for the single-gusset joints are shown in tables 1, 2,
and 3 (see footnote 6 of the tables).
Because this type of joint is of a severely unbalanced construction,
more deformation and resulting rupture in the wood occurred with these joints
than with the double-gusset type. It appeared that, even when strong and
durable glue joints are provided, the single-gusset construction is unsatisfactory when severe moisture changes are involved, especially with species
such as oak.
Effect of Gluing Pressure
As previously stated, the majority of specimens were made with
carriage bolts (spaced as shown in fig. 1(A)) to supply gluing pressure. At
several temperatures, however, a number of specimens were included for which
clamps and cauls were used to furnish pressure. These specimens were all
tested by the accelerated vacuum-pressure method (exposure I), and the
results are shown in tables 1, 2, and 3. There was some indication that the
clamping produced better bonds than the bolt pressure, but the limited number
of specimens would not permit a definite comparison.
Weathering Exposure
In general, 10 months of exposure to the weather did not add appreciably to the joint failure of specimens previously subjected to exposures I,
II, or III. In the specimens made with mahogany and with Sitka spruce frame
members, there was practically no change; and in those made with oak frame
members, the additional amount of open joints was slight and usually confined
to specimens glued with urea resin, while those glued with resorcinols
remained essentially unchanged.
Summary of Results
Graphical presentation of results is shown in figures 13, 14, and 15.
Figure 13 shows the resistance to delamination of resorcinol-, urea-, and
casein-glued joints cured at temperatures of 40° to 80° F., inclusive. These
joints were all made with exterior-grade Douglas-fir gussets and white oak
frame members. Values shown for resorcinol glue are averages for three
joints, each made with a different glue. The values for urea and casein are
based upon results with one glue of each type. The results from joints made
with bolt pressure only (table 1, exposure I) are included in figure 13.
Report No. R1714
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At the higher curing temperatures, the urea glue showed somewhat
better performance than the casein glue. The performance of each of these
glues, however, was distinctly inferior to that of the resorcinol glues. The
resorcinol adhesives showed best performance when cured at 80° F., and a
general slight decrease in bond quality as the curing temperature was lowered.
The results at 40° F. were about the same as at 70° F. The reason for the
apparent decrease in the quality of bonds curing at 50° F. is unknown.
The effect on glue bonds of the species used for frame members is
shown in figure 14. With each type of glue, resistance to delamination was
greatest with spruce frame members, less with mahogany, and least with white
oak. The difference between species was least with resorcinol, greater with
urea, and greatest with casein glue.
The resistance to delamination under three different types of exposures of assembly joints made with white oak frame members is shown in
figure 15. The accelerated vacuum-pressure soaking-drying cycles caused
the greatest amount of delamination with each type of glue. Salt-water
soaking-and-drying cycles were second in order of severity, and the high
temperature followed by high-humidity cycles caused the least amount of open
joints in resorcinol- and casein-glued joints. In the case of urea-glued
joints, the high temperatures followed by high-humidity cycles were more
severe than the salt-water soaking-and-drying cycles.
In previous work at the Forest Products Laboratory, there has generally
been little difference in effects upon glue bonds between the vacuum-pressure
cyclic test and the 30-day soaking - 30-day drying cycle when the drying has
been carried out at 80° F. and 30 percent relative humidity in both tests.
In this study, however, the drying conditions were much milder for the
straight soaking-drying test during the latter half of the test period, which
undoubtedly accounted for the difference in results between the two test
methods. The straight soaking- drying test was used because it can be
carried out in shops or plants where no rooms with controlled temperature and
humidity are available.
Conclusions
The results of this study furnished bases for the following conclusions:
1. The durability of resorcinol glues in well-made boat-frame assembly
joints subjected to severe exposures was superior to that of casein and urearesin glues. Double-gusset assembly joints combining framing members with
exterior Douglas-fir plywood and glued with resorcinol glues were strong and
durable enough to resist glue-joint delamination under exposure conditions
including severe soaking and drying,
2. Resorcinol-resin glues produced bonds that were durable under
severe exposures at curing temperatures as low as 4+0° F. in assembly joints
involving such combinations as mahogany lumber and Douglas-fir plywood,
spruce lumber and Douglas-fir plywood, and at curing temperatures of 70° F. or
Report No. R1714
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higher when white oak lumber and Douglas-fir plywood were used. Some
resorcinol glues, however, were satisfactorily used at 60° F. with the combinations involving oak.
In a straight soaking-drying cyclic test, joints of the oak-fir combination performed satisfactorily when the glues were cured at temperatures
as low as 40° F. (A two-week pressing period vas used for all curing
temperatures, and the minimum permissible pressing time was not determined.)
In addition to these principal conclusions, the study also provided
the bases for the following conclusions:
3. Combinations of such materials as flat-grain white oak and
Douglas-fir plywood in assembly joints of the type used in this study did
not appear to be entirely satisfactory for extreme exposures. Due to the
great dimensional changes of flat-grain oak with extreme changes in moisture
content, the wood ruptured even though the glue bond remained intact. Good
paint protection that would retard the moisture changes would minimize the
tendency toward failure.
4. An assembly joint involving frame members joined by a single
gusset (figs. 1(B), 11, and 12) appeared to be a less satisfactory glued
construction than the double-gusset typo of joint (figs. 1(A) and 3) under
conditions involving extreme exposure.
5. With favorable combinations of species and glue, the use of clamps
for applying gluing pressure with resorcinol glues appeared adequate for the
assembly gluing of joints between plywood gussets and framing members of the
type generally bolted and glued. In such cases, the joint was durable under
extreme conditions of exposure to moisture, and bolts were not necessary.
The omission of bolts would result in an appreciable reduction of weight in
constructions where a large number of bolted gussets are normally employed.
Report No. R1714
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Table 1.--Remulte of three differ-en o ollo ex p osure teats on us$at-t - aseemb
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delemination in wood:
tdelamination:in woods
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0
0
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1
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i
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.
;
.
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:
1
:
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0
0
0
:
:
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.
A
s
:
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t
:
s
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1
:
0 : 1
;
•
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:
.
•
0
: 1 : 1
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:
•
70
: Bolts
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:
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:
:
:
80
80
80
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B
1
:
: do.
: do.
.
: Clamps
s
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: do.
.
!
70
:
46
:
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:
282
:
80 .5
0
:
:
.26
1
1
:
0
:
:
:
0
2
C
:
80
80
80
A
A
:
:
80
80
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: Clamps :
0
A
B
C
80
80
80
: Bolts
: do.
: do.
1
0
0
D
E
80
80
:
:
:
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0
.
:
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8 : 51:
0 : .26
3
1
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8
1
3
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4
: 0 : a82
i 0 i 0
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Specimens Painted Prior to Exposure
do.
1
4
49
28
580
:
:
1
i
t
0
0
o
7
:
:
1
.
:
0
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56
0
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1
51 : 53
: 520 :5100
1 28 : 282
574
.
.
.
•
l.T-he indicated temperature was maintained for 2 weeks, after-1110h the gluing pressure was released and the exposures
started. (For'the casein-glued specimens the bolts were left in place during the testing.)
lExposure I . accelerated vacuum-pressure soaking-and-drying cycles: exposure II • salt-water soaking-and-drying cycles;
exposure III high-temperature, low-humidity and room-temperature, high humidity cycles. These tests are described
on pages 5 and 6 of the report. All results are values observed after 6 months' exposure.
lOpen-joint-area percentage le based upon the total area of assembly glue joint in the specimen.
AEach value shown is the result for one specimen.
Values obtained after the bolts bad been removed and joints pried apart. The values shown immediately above were
obtained while the bolts remained in place, whioh made acourate measurement of the open-joint areas extremely difficult.
/These specimens were of the single-gusset type (fig. 1,B); all the others were of tbedouble-gusset type (fig. 1,A).
a )1 77986 F
do.
:
Table
2L--a"2:=
at various to®gersturee
Joints made with matoganp frame masbers
: Gluing : Method • and
:
of
:
Exposure 12Exposure•II
Exposure III
: outlnir:applying: :
:
:temp a-1.: gluing :
Open-joint area
:
Open-joint area
.
Open-joint area
turea :pressure: : Glue-joint :Rupture: Total : Glue-joint :Rupture: Total i Glue-joint :Rupture: Total
:delamination:in wood:
:delamination:in wood:
:delamination:in wood:
:
• • P :
: Percent ! ercent!Percent: bEltaI lercent :peroent: Emma :percent Percent
4
:
40
i Bolts :
-0
:
0
:
0
:
0
:
0
:
0
0
:
0
:
0
:
40
i
do, :
0
:
0
0
:
:
o
: 0 : 0
0
:
0
:
0
:
40
:
do, :
0
: 0 : 0 :
0
: 0 : 0
0
: 0 : 0
Glue
P
•
B
C
A
13
C
ii
:
60
60
B
a
i
'
i
60
60
4
A
pppx
B
0
I
Is
1111
:
:
:
:
:
:
70
20
70
do. :
do, :
do, •
0
6
0
do, :
100
do, :
do, :
do, :
0
10
0
Clamps :
do, :
do, :
: Bolts :
:
do, :
70
:
70
:
70.:
A
B
0
D
1
E
60
60
60
ao
A
D
E
:
:
:
60
D
A
B
C
60
50
60
do, :
do, :
do, :
: Clamps 1
:
do, :
:
do, :
70
: Bolts :
70 : dq :
.•
A
B
0
A
B
0
A
A
:80:
80:
80:
0
10
2
26
5 8
-66
:
:
:
:
80: Clamps 1
80: do.
:
80
: do.
:
.
: Bolts i
: Clamps a
0
0
0
:
:
:
0
3
0
:
:
:
:
:
:
0
0
0
0
: 10
:
:
12 1 :
0
: 20
:
•
:
9
69 :
.
:
0
:
2
:
0
:
:
:
•.
•.
a
2
14
A
0
1
0
0
:
2
0
0
:
:
0
3
:
:
0
:
0
:
:
0
: 50
: '-8
..•.
.
.
•
0
:
4
1
:
54
- 10
0
0
0
0
0
0
0
0
0
:
:
:
.
:
:
:
0
0
0
0
:
:
0
:
:
:
0
4
0
0
:
0
0
0
:
0
0
:
:
0
0
0
:
:
0
:
0
0
:
:
0
0
:
:
0
0
0
:
1
:
.
1
0
1
0
o
1
0
1
0
1
:
:
.
.
.
0
:
:
:
:
..
1
1
118
0
0
0
•
:
0
:
: A0
: .312 :
111
:
:
:
0
0
0
:
:
:
.
0
0
0
•.
.•
:
:
:
, 6
1
0
; = 10
1
6
:
0
0
1
:
:
:
:
.0
.- a
:
:
:
0
.
0
0
0
0
0
0
:
!
1
:
.
.
.
:
:
1 - :
0
:
.
o
:
.'
:
.
0
0
0
0
:
:
o
:
5
:
:
0
•
2
:
: 0 : 14 :
1
:
.
:
•
.
•
.
.
:
: 10
: . 3
E.08
0
.
:
:
:
.
:
0
0
0
0
0
.
10
53
-47
.
:
:
:
.
..
0
0
0
:
•.
:
4;1
0
0
0
3
0
:
:
0
0
0
0
0
0
0
0
.
:
0
0
0
:
:
0
0
E
:
0
: 16
•
0
0
1
.
:
0
:
:
:
: 0 : 100
:
.
0:
2
:
0
:
..
do,
dq
do,
:
:
:
0
:
1.3
::
0
60
-/
•
.
:
:
:
0
0
0
:
:
:
0
0
0
:
:
0
:
0
:
0
0
: 0
:
0
0
0
•
. 6_2.
: .-13
1
: Ai
1 la a
1Tho indicated temperature was maintained for 2 weeks after a which the gluing liesare was released and the exposures started.
2 [Por the caeein-glued sp ecimens the Dolts vere left. in pl
urine tne tea ng.
-xposure
E
aonelerated vacuum-measure
0y010111 exposure
alt-water soaking-and -drying oycles:
exposure III high - temperatu • e,los- humidity and room-temperature, high-humidity cycles. These tests are described on
pages 5 and 6 of the report. All results are values observed after 6 months: exposure. •
lOpen-joint-area peroentage is based upon the total area of assembly glue joint in the specimen.
AXaoh value shown is the result for one speoimen.
Values obtained after the bolts had been removed and joints pried apart. The values shown immediately above were obtained
while the bolts remained in place, which made accurate measurement of the open-joint areas extremely difficult.
',These specimens were of the single-gusset type (fig. 1,13): all the others were of the double-gusset type (fig. 1,A).
IR 779117 r
Table 3.--RIP44
Don•.s-fir
nod
▪ tn
- -Zn"113117r_LUTIVIINZI •
or caaeln u us, our* at various tempsrature n
: Gluing : Method :
and :of
Glue
:tempera-1
Joints made with Oitka spruce frame members
:
,
curing :applying:
B
40
40
C
40
A
B
C
60
50
60
2: Exposure II
: Bolts :
:
do, :
I
do.
4
-0
0
:
0
0
0
:
:
0
0
0
,
:
:
0
0
:
:
0
1
:
:
0
0
:
:
0
I
:
:
0
0
:
:
1
:
:
:
0
D
80
.100
:
0
60
60
60
:
:
:
do. :
do. :
do. :
0
1
0
t
:
:
:
:
0
A
B
0
0
:
:
;
:
0
0
0
C
60
80
60
: Clamps :
:
:
do.
:
do,
:
0
0
0
:
:
:
0
0
0
▪: :
:
0
0
0
D
E
60
60
: Bolts :
:
do.
•
11
512
-97
A
B
a
70
:
C
i
70
70
do. .
:
:
C
I
A
B
11
do,
do.
do.
0
do. .
100
.
.
B
:80:
a
0
do.
:
0
0
:
0
:
0
1
0
do.
:
0
4
5
:
t
.
•.
0
0
0
I
:
I
:
Open-joint area
0 :
0
0
0
;
:
0
0
0
0
0
.
•
•.
:
:
0
:
.
0
:
0
•••
0
▪:
0
:
0
4•
0
140
0
:
0
:
0
:
0
:
0
:
i
0
0
: 0
:
0
:
0
0
:
0
1
.
:
0
•.
:
0
:
0
t
:
:
:
0
:
0
4
:
6 1
'-25
:
0
:
0
i
0
:
0
1
1
1
I
:
I
1
:
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0
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50
: 6 2
-3 ; -19
.
;
:
:
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:
:
I
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.
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•.
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0
:
0
:
0
0
0
:
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1
0
0
0
:
0
:
1 0
:
1
: -25
s
:
:
:
0
0
0
:
:
0
0
0
:
•
•
0
0
0
:
1
0
0
0
50
0 : -0
0
0
1
1
0
0
0
2
0
.
0
0
:
0
t
le
.
.
•
•.
.•
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•
.
e
.
•
0
I
:0:0:
:
0
:
0
:
1
:
g
0
t
1
.•
•
•
:
'
:
:
•
:
0
t
•.
•
•
:
:
0
..
:
;
:
0
0
0
s
0
0
.
0
0
0
I
0
0
0
t
:
:
g , '2.
0
;
0
1
:
1
0
0
0
:
.
:
0
:▪
1
0
0
•.
Ste
0
0
'
0
0
0
1
5 2
0
0
0
•.
.•
:
0
:
0
0
:
1
0
0
0
0
t
t
0
0
:
:
15 5
-6
,
0
;
:
4
5
:
0
0
:
0
:
0
. 0
0
0
0
:
0
0
0
:
.
:
: Bolts :
A
:Clamps
;
A
:
0
0
•
0
3
:
0
•.
:
do. :
: Clamps :
do. :
:BO:
do. 2
:
:
•.
:.
0
;
T
0
:
: Bolts .
:
do.
•
.• 80:
do.
BO:
do, .
:. do, :
2
:
1
70
70
1
0
0
1
•.
D
E
A
•
,
0
1
C
C
:
:
:
A
B
0
0
: Clamps :
:
do,
:
:
4
54
-8
70
:
.
0
:
70
70
B
:
0
:
: 11
:
0
: 6 l2
: 0 :-97
I
A
III
4
0
:
:
:
.
:
.
Imposure
i
--- Open-joint area
:
s
1
:
i
Open-aoint areal:
Glue -point :Rupture: Total : Glue-joint :Rupture: Total : Glue-joint :Rupture: Total
:delemination:in wood:
:delemination:in wood:
:delesinetionan wood:
•
'
:
4
1
:
•
4
: !mass :Percent:Eu=9F Percent :Percent:Percent: Percent :Emma:Emma
:
•
: • F •
A
'Exposure
gluing : : tune :pressure:
I
xn
▪ q n n ure
- Imo
0
O
:
I
s
'The indicated temp erature was maintained for 2 weeks, after which the gluing pressure was released and the exposures started.
(For the casein-glued ape:Amens the bolts were left in place during the testing.)
aExposure I = accelerated vaouwn-pressure soaking and-drying cycles; exposure II salt-water soaking-and-drying cycles;
exposure III - high-temperature, low-humidity and room-temperature, high-humidity oyolee. These tests are described
on pages 5 and 6 of the report. All results are values observed after 6 months , exposure.
3-Open-joint-area peroentage is based upon the total area of assembly glue joint in the specimen.
AEach value shown is the result for one specimen.
.Values obtained after the bolts had been removed and joints pried apart. The values shown immediately above were obtained
while the bolts remained in place, which made accurate measurement of the open-joint areas extremely diffioult.
-These specimens were of the single-gusset type (fig. 1,8); all the others were of the double-gusset type (fig. 1,A).
M
77988 I
P ! 2 3
4
SCALE IN INCHES
A
4
4
HOLES FOR
4" CARRIAGE BOLTS
ce-
-9
__L_ •
=c"rr•
O I 2 3 4
SCALE IN INCHES
B
Figure 1.--Two types of assembly joints. (A) Double-gusset type made with 3/4-inoh
lumber (white oak, mahogany, and spruoe) and 3/8-inch Douglas-fir plywood
gussets. (B) Single-gusset type made with 3/4-inoh lumber (white oak,
x sum r
mahogany, and spruoe) and 3/4-inoh Douglas-fir plywood gusset.
HOLES FOR
CARMASE DOLTS
A
B
7 4
SCALE /N INCHES
9 f t J 1
SCALE /N INCHES
Figure 2.--Two different bolt spacing patterns used in gusset-type assembly joints.
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LEGEND:
- RESORCINOL RES/N GLUE
MUREA RESIN GLUE
CASE/N GLUE
NOTE; UREA AND CASE/N NOT INCLUDED
/N TESTS AT 40° AND 50°F.
70
Figure 13.--Effect of accelerated soaking and drying cycles
(exposure I) on assembly Joints made of exterior-grade Douglasfir plywood gussets and white oak frame members and glued with
resorcinol, urea, or casein glue.
Z K 739gO F
80
100
LEGEND:
8O
W = WHITE OAK
1E22M = MAHOGANY
MIS = SITKA SPRUCE
tu
p 60
w
Lu 40
L
20
w
sAIV
•11
• 40.
444
0
RESORCINOL
UREA
CASE/N
TYPE OF GLUE
Figure 14.--Effect of species on glue bonds in gusset-type assembly
joints made of white oak, mahogany, or Sitka spruce frame members
and exterior-grade Douglas-fir plywood gussets, and glued with
resorcinol, urea, or casein glue. Each glue was cured at 70° F.
x 73975 7
100
LEGEND:
Ko:4; I= ACCELERATED VACUUM—PRESSURE
SOAKING AND DRYING CYCLES
®.17= SALT WATER SOAKING AND DRYING CYCLES
= HIGH — TEMPERATURE LOW—HUMIDITY AND
ROOM— TEMPERATURE HIGH — HUMIDITY CYCLES
tu 80
1/43
O
60
•=4
O 40
O
tiu
BO
O
RESORCINOL UREA
TYPE OF GLUE
Figure 15.--Effect of three different exposures on resorcinol-,
urea-, and casein-glued assembly Joints made with exteriorgrade Douglas-fir plywood gussets and white oak frame members.
Each glue was cured at 70! F.
Z M 73979 11
CASEIN