By C.E."Chuck" Ring
I operate
a one person business building furniture, bookcases, cabinets,
interior/exterior residential doors, shutters and other millwork.
I was initially attracted to polyurethane adhesive due to
the long open time it affords. My shop is located outside
of Albuquerque, New Mexico and is situated at an altitude
of 6400 feet. Humidity is almost always low in this locale
and temperature swings from daytime hours to nighttime hours
can be extreme. Differentials of thirty degrees are not uncommon.
I heat my shop during the colder months with a wood burning
stove, but even without the heating, the temperature in the
shop never drops below 40 degrees Fahrenheit, due I am sure
to the insulation I took care to install. During the summer
months the temperature in the shop never goes above 80 degrees
Fahrenheit. I furnish this information to inform you of my
working conditions, so you will have a better understanding
of how polyurethane adhesives have worked for me.
What follows is not to be a scientific study on the use or suitability
of polyurethane adhesives....Rather, it will hopefully answer
questions concerning its suitability for woodworking applications.
I have used polyurethane adhesives in various joinery applications
for at least two years. During this period of time, I have
found it to be very useful when multiple components must
be assembled and polyvinyl acetates and similar faster setting
adhesives would not serve well due to their relatively short
open times. For the sake of brevity, I will refer to polyurethane
adhesives as "poly or polys" for the remainder of this article.
While I am a fan and advocate of polys, I urge anyone contemplating
their use to satisfy themselves as to the value and practicality
of this material. What has worked for me and others may
not work for each individual user due to climatic and material
conditions at your shop/work site. So, before opting for
polyurethane adhesive for that expensive piece or pieces....Test
!.
As
pointed out above, polys in general have a relatively long
open time when compared to polyvinyl acetates and similar
faster setting adhesives. Because polys use moisture present
in the atmosphere and in the material being assembled, clamping
and cure times can vary. Higher relative humidity and higher
moisture content in the wood itself hastens cure time. Ambient
temperature and the temperature of the materials also have
an effect on the cure rate, but probably not to the extent
that moisture does. Some users of polys, including myself,
wet/moisten the components to induce more rapid cure times
and to insure there is enough moisture to allow the adhesive
to cure effectively. How much moisture to add is best left
to experience, however, I have found if the wood changes
to a darker shade from the application of moisture, it is
adequate. You should not be overly concerned about adding
too much moisture as most suppliers of polys state the adhesive
is effective on wood which has a moisture content of eight
to twenty percent.
Polys seem not to mind if the edges or surfaces being joined are
milled to a smooth finish. I have joined components straight
from ripping on the table saw and found the wood failed
and the glued joint held fast when the joint was stressed.
One supplier, (Excel) even states in some of their printed
material surfaces are best left in a "roughened condition".
Before the poly cures, any excess can be removed with acetone,
denatured alcohol, or mineral spirits. Fully cured poly
is easily removed with a wood chisel or scraper and it can
be sanded without filling the sanding material with residue.
Before you get the glue bottle out....Unless you are excessively
neat and careful, you should plan to wear some sort of cover
or barrier on your hands. I use latex gloves and have found
if I am careful, I can use the gloves on several operations
(no pun intended). For those who are allergic to latex,
try rubber or perhaps one of the barrier creams will work.
If you choose not to cover your hands and you get the poly
on your skin you will have to use one of the solvents listed
above to remove it or you will have to wear it off over
a period of three to four days. Once the poly dries, soap
and water offers no remedy for the brown stains which will
appear on your skin. I believe all of the mentioned solvents
can be absorbed through the skin, therefore I suspect the
less applied to the skin for cleansing, the better.
While I have no desire to be controversial or stray from the accepted
path of acceptable woodworking and adhesive practices, I
have used polys for plate joinery and continue to do so
to this date. Experiments I have participated in as a principal
at Sandia National Laboratories and simple shop tests I
have conducted on my own convince me the method is appropriate
and long lasting. For some information concerning the results
of the Sandia tests you might want to refer to articles
in American Woodworker (issue #50) and Fine Woodworking
(issue #118). I have been and am still attempting to get
a comprehensive posting of the tests results posted on Sandia's
website.
For the present, I can relate to you my personal experience
in using Lamello S-6 bisquits and polyurethane adhesives
in the construction of interior and exterior residential
doors. Eight doors which I made from Ponderosa pine (one
exterior, seven interior) have cycled through two winters,
1 1/2 summers, two adults and four rug rats. I have the
opportunity to examine the doors on a weekly basis and have
found no separation at joinery locations or any warping,
bowing or other problems. The exterior door has been subjected
to driving snow, rain, and dust. Although I have made thirty-four
other doors using the same methods, they are not available
to me for constant observation, but no client has indicated
any problem with any of the thirty-four.
I have conducted what seems to me to be endless shop tests of polyurethane
adhesives and woodworking materials. One of my friends,
tiring of my never ending daily reports to him started calling
me "The Guru Of Glue", I sort of liked the title, but turned
the phrase a little and changed it to "The Gluru Of Glue".
Please don't infer from this account that I fancy myself
an expert with polys or any other adhesives, just a little
aside and an attempt to impart some humor in this article.
Many of my tests in the shop involve trying to determine what
happens to a bisquited joint when glued with poly. By way
of explanation, after cutting the slots and applying the
adhesive in the slot and on the surface grain of the components,
I dunk the plates in a container of water and remove them
right away. I then place the plates in their slots, assemble
the components and clamp for the appropriate period of time.
I try to plan my assembly and glue-ups so I can leave everything
clamped overnight. This generally works for me, but may
be a little overkill for those in higher humidity locations.
After the adhesive has cured, the clamps are removed and
I subject the joint to varying degrees of stress. Sometimes
the assembly is placed in a vice and struck with a hammer.
I have found the joints to be on a subjective par with joints
assembled with PVA adhesives. More importantly, some of
the samples are sawed across the joint location , so that
the space between the bisquit side and the wall of the slots
can be observed. My fifty-six year old bifocal aided eyes
have thus far, be unable to discern a glue line, much less
unfilled space. A 6X power, cheap magnifying glass, also
fails to reveal any space at the location. The excess space
at the ends of the bisquits are usually filled with cured
adhesive. When I try to remove the bisquit portions by levering
with a scratch awl, I find the plate material comes out
in very small portions, sometimes bringing some of the wood
from the wall of the slot with it. This compares to the
same general results with joints assembled with PVA adhesives.
In addition to the above tests/experiments, I have made sample
joints using various poly products to edge join and butt
join various materials. One of the most striking experiments
involved gluing two pieces of Yellow Poplar end grain to
edge grain. Both pieces were five inches wide and eighteen
inches long. After an overnight cure, I placed a corner
of one of the legs of the angle formed by the components
on the floor and placed all of my weight on it. The joint
did not come apart from my weight and a repeat of the process
by two of my bigger friends failed to fracture the joint.
Eventually, I became tired of walking over and around the
piece and whacked it with a 16 ounce framing hammer. The
joint finally fractured but not at the glue line. Approximately
one half to one inch of wood came away on one of the components.
No mechanical means of strengthening the joint were utilized.
Just polyurethane glue and wood.
I have become email buddies with Mr. Don Watland of the Phoenix,
Arizona area. Mr. Watland runs a one man operation (Watland
Design) and makes traditional and contemporary furniture.
My first email contact with Mr. Watland came after I saw
a post of his on the user group "rec.woodworking". In his
post Mr. Watland related he had been a user of polyurethane
glue and bisquit combinations for over a year. His experience
with the glue and bisquits closely tracked mine, so I asked
him to share some of his methods and results with me and
the readers of this article.
Mr. Watland has advised me he also wets the bisquits before
inserting them in the slots. He relates that after wetting,
the bisquits quickly swell to fill the slots to the point
they can not be easily repositioned. Mr. Watland's experience
had up until recently been with Gorilla only. He has recently
obtained a sample of Excel regular, but has not put it through
it's paces. In addition to edge joining plywood, Mr. Watland
has bonded acrylic sheets as thin as 1/8" to wood members
with slots or rabbets to receive the acrylic for 90 degree
and "flat" joints, he has bonded Kortron to itself and to
solid wood, and he glued up an "L" shaped bar top from sections
of 3/4" ash veneered plywood which was edge joined in several
places. Mr. Watland states his procedure for gluing the
Kortron was to sand the surface of the Kortron with 80 grit
sandpaper to the point that the shiny/slick surface of the
Kortron was "roughened". His bar top was able to hold his
weight when he cantilevered it over his workbench top. Mr.
Watland still uses and likes white and yellow glues, but
does reach for the polys when he needs extra assembly time
or there is any question about that aspect of his operation.
He has also found it performs extremely well with woods
such as ebony and rosewood.
Within the last few days, I used Excel Regular and Excel Express
to glue up two samples of white Melamine (melamine to melamine),
I applied moisture to one of the surfaces of each sample
and allowed it to cure overnight, (approximately 12 hours).
When I placed the samples in my vise and struck them with
a metal hammer the joint fractured into the particleboard
substrate all along the glued portion. Both samples displayed
the same results.
One final glue story and I'll provide some new information on
new products and the opinion of at least one of the present
suppliers of polys.....I cut sized pine plywood pads for
all of my bar, pipe, and similar clamps, applied poly to
the wood, and placed a pad on each of the metal heads of
each clamp and then slid the pads together and applied light
clamping pressure until the glue was cured. You don't need
a lot, just enough to cover the surface, (be careful not
to get any glue on the face of the pads, you don't want
to lock them together , do you?). This was done over a year
ago and I have not lost a pad to this date. Be sure to raise
the plywood high enough so it doesn't touch the bar or pipe
or it will not move smoothly in operation. If your pad becomes
worn/damaged you can remove it with an old chisel or other
sharp object.
I have mentioned a product currently called Excel Express. This
product is a thixotropic gel. My understanding is that thixotropic
means, it liquefies when subjected to motion. If such is
the case this product lives up to the description as when
it is brushed or otherwise moved it does liquefy. Unlike
"regular" polys this product cures for clamp removal in
my shop in less than thirty minutes and starts to foam almost
immediately. My impression is, it is stronger(my subjective
opinion) and more gap filling than regular polys. This product
comes in a tube similar to a regular caulk tube and is used
with a caulking gun. At first I found this methodology to
be cumbersome, however after conducting several shop tests,
I found it did not slow me down when I applied it to bisquit
slots or regular edge or other joints. I also worried that
the glue in the tube would dry out like caulk often does
even when a cap or wire nut is placed over the spout. I
actually found if the excess glue which might come out of
the spout is allowed to cure, when you get ready to use
the adhesive again, you just remove the cured portion and
fresh, uncurl glue presents itself. I was lucky enough to
acquire sufficient of this glue to use it on some of my
projects. In all cases it exceeded my expectations. This
product is poised for marketing in late summer and will
probably be more expensive than the regular polys. I am
not positive what stores will be carrying it, but I would
suspect Woodworker's Supply, Trend-lines, and other stores
which presently carry Excel product will opt to carry the
Express.
I recently purchased a product from Custom-Pak Adhesives labeled as
RPA. I believe the letters stand for Reactive Polyurethane
Adhesive. Open time for the product is stated as 15 to 20
minutes and clamp time about 90 minutes. Shelf life is given
as" up to four months in a tightly closed container in a
cool dry environment". I performed my "standard" double
bisquit butt joint test with two sample joints. Left to
cure for about 12 hours this product performed very well.
When sawed apart and examined with my "magic" cheap magnifying
glass I could discern no glue line and all of the excess
slot space was filled with cured adhesive. I would have
liked to have performed additional tests with this product,
however the deadline for this article caught up with me
and I was not able to do so. I was not asked to, but I did
provide Custom-Pak with my short evaluation of the product.
I also indicated to them I thought the product was a little
pricey for adhesive with a shelf life of four months. The
18 ounce container was purchased for eighteen dollars. Upon
further thought and in retrospect, I believe I might have
been hasty in complaining about the price and the shelf
life. For one thing...All polys go a long way and you do
not have to apply the products to both surfaces...For another
I would use the 18 ounces before the shelf life expired.
As a final observation concerning RPA, I noted it cures
to a white color very similar to Excel Express.
I believe that any of the liquid or gel poly products I have worked
with or tested are very good products. I'm not here to endorse
one over another. I know my shop tests are not scientific
and I have used the product in some applications which are
not recommended.
Examine the results I have tried to present to you, perform
your own evaluations/tests and decide for yourself if polys
are a real option for you. In some applications you'll decide
polys are overkill, but you may find a new and efficient
partner to help you in some operations. Finally, I have
not addressed the issue of whether or not the poly products
are "waterproof". Some labeling and product literature indicate
it is. I don't believe all of the product, if any, currently
on the market in the United States has been subjected to
strict independent laboratory testing to determine to what
extent it really resists water when cured. Perhaps in the
not to distant future, tests will be performed which will
answer the question. To paraphrase, a comment by Mr. Sammy
Mayeaux of Ambel Corporation, (Excel Distributors).... What
we see now in polyurethane adhesives is just the tip of
the iceberg!
In closing I would like to acknowledge the help given to me
by Mr. Don Watland of Watland Design, Mr. Sammy Mayeaux
of Ambel Corporation, Mr. Jeff Pitcher of Custom-Pak Adhesives,
Inc., the folks at Gorilla Group, and Mr. Eddie Sirotich
of this website. Certainly any lack of content and writing
ability is my responsibility and fault. I hope if you have
questions or comments (be gentle) you will present them.
C.E.
"Chuck" Ring
Madera Encantada "Enchanted Wood"
e-mail: cring@concentric.net