n the early 1990s, I moved back to
I New Orleans after spending many
years working as a carpenter in Cali-
fornia. At that time, my knowledge of
adhesives could be summed up in two words:
yellow glue. Wherever I needed to join two
pieces of trim—whether inside or outside—
I’d squeeze out a dab of glue, nail the wood
securely, and forget about it—only for a while,
as it turned out. My cavalier approach to join-
ery may have been acceptable for the benign
California environment, but not for the sweaty
pressure cooker that New Orleans residents
laughingly call a climate. After a year or two
of seasonal movement, many of the joints I
was so proud of had separated, giving moisture
Three and rot a clear shot at vulnerable end grain.
Since then, I’ve experimented with more
than a dozen adhesives marketed for exterior
use, and I’ve regularly monitored my cre-
Tough Glues
ations to see how they’ve held
up. Although other glues have
their advantages, I’ve settled on
three that are particularly effec-
tive for my work and my location:
for Outdoor Use For simple, tight-fitted joints, I use polyure-
thane glue; for clamp-free assemblies and
gap-filling, I use hot-melt polyurethane; and
The right adhesive will keep joints for extreme conditions, I use marine epoxy.
tight and wood from rotting No glue is totally waterproof
As far as I can tell, old-time carpenters nev-
BY JOHN MICHAEL DAVIS er used any kind of glue outside. They, how-
ever, had the advantage of building with
old-growth lumber species that were rock
stable and highly rot-resistant.
Gluing exterior joints gives the inferior
grades of lumber that we have to work with
nowadays a fighting chance by sealing the
grain of the wood and keeping the joint from
opening up to allow water to get to that grain.
But you can’t rely on glue alone. Despite what
some manufacturers might claim, no glue is
100% waterproof. Engineers tell me that the
best glues are merely more water-resistant
than their competitors. Given enough water
and time, every glue joint will fail. So no mat-
ter what adhesive you choose, you always
should design the joint to shed water, and you
should keep it well painted.
I’m a working carpenter, not a scientist. I
can’t provide a technical article full of for-
mulas and properties of each glue type. But
I can offer a hands-on account of what works
best for me in an unforgiving climate. If you’re
building in Pasadena, yellow glue might be
the only two words you need to know.
No mixing, no waiting.
Although it’s not the
strongest exterior adhe-
sive, its all-in-one-bottle
convenience makes
polyurethane glue the
Dried polyurethane perfect choice when
glue won’t come off your your time is limited.
hands until the skin cells flake
off, so always wear gloves.
POLYURETHANE GLUE IS CONVENIENT BUT MESSY
P
Dry wood olyurethane glues first appeared about 10 years ago. The Gorilla
won’t bond.
brand (Lutz File & Tool Co.; 800-966-3458; www.gorillaglue.com)
Polyurethane glue
requires moisture is the most prominent player in the market, but I haven’t found any
to cure. If the difference between it and less-expensive choices, such as Probond
moisture content (Elmer’s Products Inc.; 800-848-9400; www.elmers.com). As a single-
of the wood is be-
part glue that’s ready to use right out of the bottle, polyurethane is
low 10% or if the
wood just looks the most user-friendly adhesive in my arsenal. When I’m trimming a
dry, mist one sur- cornice 21⁄2 stories up, I particularly appreciate the convenience.
face (or wipe it By the numbers, polyurethane is not quite as strong as a premium-
with a damp cloth),
quality type II carpenter’s glue (sidebar p. 52), but it’s much more
then apply glue to
the other surface. water-resistant. Among its other advantages, polyurethane glue is eas-
ily sanded (photo bottom right); dries quickly, especially in heat and
humidity; and bonds to wet wood.
Polyurethane requires moisture to cure, so dry wood must be wet-
ted before glue-up (photo top left). As it’s curing, the glue expands con-
siderably (photo bottom left), but the foam has no structural strength.
A high-strength bond requires tight, well-clamped joints.
Despite its benefits, polyurethane is the messiest glue I’ve ever used.
The amount of squeeze-out from the foaming action is unpredictable
and all but impossible to clean up until it’s cured. Any finished surfaces
beneath the joint should be covered to protect them from drips. Latex
gloves are a must; if you get wet glue on your skin, it’s going to stay
there for days.
Polyurethane is expensive. It costs at least twice as much as standard
yellow glue, and the shelf life is much shorter, especially once the bot-
tle has been opened. In fact, when I started using it, I kept having prob-
lems with it hardening in the bottle, often just a day or two after the
bottle had been opened. These days, I buy the smallest bottles I can get
Let dry overnight, then sand normally. Until it cures, it’s a foamy and store open containers in the refrigerator; I keep them upside down
mess, but after it has had time to dry, the squeeze-out from
polyurethane glue can be trimmed with a sharp blade and then to prevent the tips from clogging and also to make sure that I don’t get
sanded smooth. them mixed up with the hot sauce.
OCTOBER/NOVEMBER 2003 51
HOT-MELT POLYURETHANE IS
FAST-BONDING BUT NOT SANDABLE
Adhesive Removable
Heating cartridge feed rod
cylinder
Corded base
station generates Trigger
heat for cordless
glue gun.
Cap for adhesive
cartridge (stored
in handle)
Fast-setting
(30 second) wood glue
P olyurethane hot-melt adhesive systems, which have been used in
industrial applications for years, only recently turned up on resi-
dential projects, but these systems already have carved out a niche. The
HiPURformer system that I use (Franklin International; 800-347-
4583; www.titebond.com) is like a beefed-up version of a hobbyist’s
hot-glue gun (photo above). Instead of glue sticks, this system uses pro-
prietary adhesive cartridges that resemble tiny caulk tubes. Unlike
Multipurpose glue typical glue guns, this one is cordless, in operation at least: Parking the
bonds a wide gun in its corded base station for 10 to 15 minutes heats the glue
variety of materials.
enough to allow about 15 minutes’ working time before the glue must
be reheated.
As with standard polyurethane glue, the hot-melt variety is very
Slower-setting strong and highly water-resistant. Unlike the bottled variety, there is
(60 second) wood glue no foam-out with hot-melt polyurethane, so it’s much less messy. If
any glue does squeeze out of a joint during assembly, it should be
wiped off immediately because it won’t sand clean once it dries. The
What we know as carpenter’s of polyurethane glue, which
Type II yellow glue is glue is technically called has much greater moisture-
strong but not so polyvinyl acetate (PVA). Type resistance. But that doesn’t
I PVA, or standard yellow mean you have to.
water-resistant glue, is intended for interior I’ve never found any
applications. Type II, which is exterior adhesive easier to
somewhat water-resistant, is use than type II PVA. It offers
intended for exterior use. For the single-part convenience
the most part, I’ve aban- of polyurethane glue, but
doned this product in favor without the messy foaming
52 FINE HOMEBUILDING
Permanent bond, almost instantly. A polyurethane
hot-melt gun applies professional-strength glue that
cures in as little as 30 seconds. A spring miter clamp
(www.right-tool.com) draws the joint tight during the
brief time it takes for the glue to cure.
viscosity is perfect: stiff enough to resist running, yet thin enough to I’ve used, including epoxy. But no mixing is involved, and pot life is
work itself into the grain. Its extremely fast dry time—from 30 to not a concern as it is with epoxy. So when I’ve got a complicated as-
75 seconds, depending on the cartridge you choose—often eliminates sembly that involves lots of small parts (photo above), I’ve found that
the need for nails or heavy-duty clamps. Hot-melt poly also can fill the hassle-free advantages offered by the hot-melt system more than
small gaps without loss of strength, and it retains a high degree of flex- make up for the expense.
ibility after it cures. The manufacturer claims that an unopened cartridge should have a
The major downside to hot-melt polyurethane is the cost. The one-year shelf life, as long as it’s kept sealed in its protective foil pouch
starter kit, which includes an applicator gun, a base station, three car- until ready for use. They also claim that a partially used cartridge
tridges, and a carrying case, requires a $100 investment. On top of that, should be good for as long as a month. In the beginning, I had trou-
the teensy replacement cartridges cost $8 each plus shipping. I ex- ble when I tried to reuse partial car-
pect that local suppliers will eventually stock these items, but in my tridges, but that was due to inexperience Homemade holster for
area, they’re available only from major mail-order suppliers such and poor housekeeping. Nowadays hot melt. To free his
hands when working
as Woodworker’s Supply (800-645-9292; www.woodworker.com) and when I’ve completed a glue-up, I break on a ladder, the author
Amazon.com (www.amazon.com). The manufacturer claims that a the gun apart immediately (top photo, made a holster for his
single cartridge will yield about 71 lin. ft. of a 1⁄16-in. bead of glue. That facing page), I wipe hot glue off the end polyurethane glue gun
makes the material cost significantly higher than any other adhesive of the feed rod, and with a glove or rag using scrap fencing
material.
to protect me from the heat, I take the
barrel and plop the cartridge out right-
side up and allow it to cool in that posi-
tion. This practice seems to keep the
action. Its viscosity is perfect strength is actually equal to
nozzle of the cartridge from clogging.
for a non-gap-filling adhesive: that of some types of epoxy.
I’ve always been concerned that the
It’s thin enough for easy If you’re not building in a
cheap-looking plastic gun might not last
application, but thick enough harsh environment and if the
long, but so far, it has done fine. For those
to prevent most runs and joint you assemble is pro-
times when I’m working on a ladder, I’ve
drips. Any drips that might tected adequately from the
made a crude holster (photo right) that
occur are wiped up easily with weather and is well painted,
isolates the hot barrel and ensures that I
a wet rag. type II PVA probably will won’t drop the expensive tool. I’ve also
Type II PVA is also incredi- work fine. purchased a few replacement feed rods
bly strong stuff; its tensile —J. M. D. because it’s only a matter of time before
that flimsy plastic thing is broken.
OCTOBER/NOVEMBER 2003 53
It starts as a liquid. One squirt each of the resin
and hardener components is pumped into a clean
container, and the epoxy is stirred vigorously for at
least one minute.
MARINE EPOXY
IS STRONG AND VERSATILE,
I f time and money were never a consideration, I’d probably use epoxy
for all my glue-ups. A top-grade marine epoxy such as the West Sys-
tem product that I use (Gougeon Brothers Inc.; 989-684-7286;
BUT COMPLICATED www.westsystem.com) fashions the most weatherproof bond and the
strongest adhesive strength possible.
With a variety of hardeners, fillers, and additives, marine epoxy is
also the most versatile adhesive available today (photos above): Mix up
the liquid components (resin and hardener), and you’ve got a bullet-
proof adhesive for gap-free joints. Stir in a thickening additive, and it
becomes the best gap-filling adhesive available. Choose different com-
binations of additives to enhance bond strength, flexibility, or sand-
Mini-pumps make the mixing ability. Choose different hardeners to control curing speed.
process almost idiotproof. Compared to the other adhesives I use, epoxy has a steeper learn-
The epoxy recipe requires sig- ing curve, but it’s not as difficult to use as some people assume. West
nificantly more resin than hard-
ener, but these dispensing System offers an excellent free technical manual, as well as an out-
pumps are cali- standing telephone support network.
brated to deliver In the large quantities I buy, epoxy requires a much larger invest-
the precise ratio ment than polyurethane alternatives, but it has a much longer shelf
in an equal
number of life, meaning I can stock up without fear of losing my investment. If
squirts. 5x I do run short, West System is readily available over the counter at
(one full pump
stroke of resin
many marine-supply stores in my area. If you’re working in the desert,
dispenses 5x it’s also available by mail order (Jamestown Distributors; 800-423-0030;
as much liquid www.jamestowndistributors.com).
as one stroke
1x The downside of epoxy is that you can’t just reach for a bottle of glue
of hardener)
or even a hot-glue gun and start sticking things together. Epoxy work
requires a full kit of tools and supplies. I have several canvas riggers
bags that are dedicated solely to epoxy work (photo bottom left, fac-
ing page). In addition to the materials themselves, these bags are
stocked with mixing cups and stirrers, plastic putty knives, disposable
paintbrushes—I mainly use 1⁄2-in.-wide plumbers’ flux brushes—sol-
Wet the joint before thickening Thickener improves workability
the epoxy. To ensure a strong and fills gaps. Adding a small
bond, both sides of a joint are amount of epoxy filler yields an all-
coated with liquid epoxy. Dis- purpose adhesive that won’t run or
posable flux brushes (available sag. Adding larger amounts increases
wherever plumbing supplies are gap-filling ability without signifi-
sold) are ideal for this task. cantly affecting bonding strength.
A dedicated epoxy kit. Epoxy work requires a myriad of materials
and supplies. A canvas riggers bag (Duluth Trading Co.; 800-505-
8888; www.duluthtrading.com) keeps all of it well organized and
close at hand.
Resin Hardener Plastic wrap for
surface protection
100-count box of
nitrile gloves
Waxed
paper for
bond
Plumbers’ flux breaker
brushes
Mixing sticks
Disposable
paintbrushes
A little squeeze-out is good.
Plastic syringes for To ensure the strongest
injecting epoxy into bond, heavily coat the joint
tight cavities surfaces and squeeze out a
small amount of excess adhe-
sive during assembly. The ex-
cess can be scraped off with
a putty knife or wiped
vents such as toluene and MEK, and plenty of rags and nitrile gloves
smooth with a dry rag. After
(strong solvents will eat through the latex variety). the epoxy is cured, a light
Even if you’re fully outfitted, epoxy is tedious work. A mixed batch sanding makes the glueline
of epoxy has a limited working life. To avoid wasting material, I often disappear completely.
make many small batches over the course of a day, then rush to com-
plete as many glue-ups as possible before the adhesive sets up.
John Michael Davis is a restoration carpenter in New Orleans.
Photos by Scott Phillips.
OCTOBER/NOVEMBER 2003 55
