Take a look at my controversial GLUE CHART
I’ll stick with hide glue. . .
© Frank Ford, 1997, 1999
Hide glue has the best characteristics for stringed instrument work, BUT it requires
care and practice to use properly. This is serious business, you really do
have to learn to work with it.
(My current glue is Milligan
& Higgins 192 gram strength high clarity. It's
water-clear when mixed, and I useabout 1.9 parts water to 1 part glue by weight.)
Mix dry glue with cold water and allow water to be fully absorbed (about an hour.)
Heat in glue pot or double boiler 145°F and stir gently until mixture is smooth
and clear. Glue must be heated (145°) for use, but may be kept for several weeks
covered in refrigerator. Discard if you notice foul odor, mold or any other contamination.
To avoid loss of strength, do not heat glue for long periods, or above 145°.
Proportions of glue and water will vary with the gram strength of the glue. Practice
with each new shipment of dry glue to obtain the ideal mixture, and mix by weight,
not volume for the most consistent results. Most of us like the glue thin enough
to just run off the brush when dipped into the heated mixture.
Joints must be clamped before glue begins to gel (around 95°.) It may help to
warm work pieces slightly or to raise temperature in workroom to prolong gel time.
Addition of urea (5-10% of the dry weight of glue) will extend gel time without
seriously decreasing strength, although it may cause a slight increase in
Hide glue sets initially by gelling as it cools. Further hardening occurs entirely
by evaporation; this process is entirely reversible. Wetting and reheating the glue
will bring it back to its original usefulness, although it is not practical in most
cases once applied to wood. If the joint doesn't go together in time, you can wash
off gelled glue with water and start over. When glue forms a “skin” or reaches
the consistency of tapioca it is too late to apply clamping pressure.
Because it sets as it gels on cooling, hide glue can be used for “rubbed” joints
where maximum strength is not required. Patches or “cleats” used to reinforce repaired
cracks may be held in place by hand, pressing hard and sliding to squeeze out excess
glue. When the glue cools, the cleat will be held in place by the gelled glue. Hide
glue shrinks as it dries, and the cleat will be drawn tighter and will have sufficient
strength in most cases.
Thinning glue excessively with water will reduce strength of the glue joint.
Wood surfaces must be well-fitted and clean. Ideally, gluing surfaces are prepared
the same day to avoid effects of oxidation. Old surfaces should be planed, scraped
or block sanded to remove oxidation. “No-load” stearate coated abrasive paper
may contaminate the surface.
Dry hide glue has an unlimited shelf life if protected from moisture.
Here's a method for preparing hide glue for quick use, without a glue
1. Weigh and mix glue with cold water; allow water to be absorbed;
heat & blend as usual. Store covered in refrigerator.
2. When you're ready to use the glue, prepare the joint, and assemble all the clamps,
cauls, and fixtures you'll need.
3. Heat a 500 ml beaker or other handy container full of water (my microwave takes
55 seconds) to 160°. (It'll cool as you go.)
4. Place a small chunk of cold glue in 1-2 oz. disposable plastic cup (like take-out
hot sauce cup) and float or clip inside beaker.
5. Use glue when it melts. After use, discard plastic cup, applicator and leftover
glue. Applicator can be cheap brush, Q-tip, etc.
Hide glue is derived from the collagen found in animal hides. It is very similar
to the gelatin we eat and is not
toxic. In the U.S. edible gelatin is made from pork skins
and hide glue from beef hides.
Glue is graded on a basis of its gel strength, a measure of how many grams
of force it requires to depress a 1/2” plunger 4mm. into a 12.5% protein solution
of the glue at 10° C. Glue is manufactured in standard grades from 32 to 512
grams. 192 gram strength is the most commonly used for woodworking; 251 is the highest
normally used for instrument building; 135 is the lowest used for general woodwork.
The higher the gram strength, the stronger the cured glue, and the shorter the working
or gel time. The lowest grades are considered strong enough for woodworking: “stronger
than the wood itself.” (Personally, I don’t think any glue deserves that sort of
comment. It may be that strong only for certain tests; it is not the same
as the wood itself.) It is never a good idea to dilute too strong a glue to obtain
lower viscosity or longer working time when it is possible to use a lower grade of
glue. Glues of different gram strengths may be mixed to get an intermediate.
I like 192 gram “high clarity” because it’s transparent and doesn't gel too fast.
Now, here's an important note. The higher gram strength glues have higher molecular
weight, which (I'm guessing here) may have slightly lower electrochemical adhesion,
i.e., they may not stick as well. Because the very high gram strength glues require
up to twice the water to reach workable consistency, there will be less glue actually
in the joint after it is clamped and the water evaporates. This may be why the very
high strength glues (300g. to 500g.) are often described in the literature as "too
strong for woodworking." Additionally, they gel too fast for many applications.
Commercial liquid hide glues have gel suppressants & remain liquid at room temperature.
They are not quite as useful for most instrument work: slightly greater tendency
for the joint to “creep,” lower moisture & heat resistance, short shelf life,
no initial tack. Many instrument makers and repairers use liquid hide glue, but they
are (or should be) careful to test each batch, in addition to watching the expiration
date printed on the bottle.
Urea will extend the working time of the glue, and will not weaken the adhesion if
it is mixed with the glue just before use. More than 5-10% urea (by dry weight) may
increase the flexibility of the dried glue; it may allow glue joints to “creep” more,
especially in heat stress. Most instrument builders and repairers try to avoid having
to use urea.
When a hide glue joint is clamped, thick liquid glue should squeeze out all
around. If the squeeze-out is “crumbly” when rubbed with a finger, or has the texture
of cottage cheese, the joint may not have been clamped in time. Excess glue should
be washed off finished surfaces to avoid chipping the finish as the glue dries and
Hide glue cures entirely by evaporation. Hide glue is about 2/3 water, and it is
important to pay attention to the amount of water absorbed into the work piece. Maple
necks can take on quite a “back bow” as a result of water absorption. Joints will
swell when glued and must be allowed to dry completely before leveling to avoid “sunken”
areas around the glue joint. Old hide glue joints can be restored by adding more
hot hide glue. The heat and moisture will reactivate the old glue on the joint surfaces,
and the new joint may be nearly as strong as the original.
Hide glue sticks to surfaces by electrochemical attraction, or specific adhesion.
Mechanical bonds, like little “fingers,” may help modern adhesives such as epoxy
because of their very high cohesive strength, but with hide glue’s low cohesive
strength, roughening joint surfaces will not help adhesion. It is better to be
concerned about the electrochemical properties of the wood.
If you'd like a whole bunch more info about hide glue, its properties and
uses, check out these FAQ pages about hide glue and player piano restoration:
Make sure the joint is clean, freshly prepared to avoid oxidation,
well-fitted and clamped in time.
North America’s only glue factory is Milligan
PO Box 506, Johnstown, NY 12095 518-762-4638 (50 lb. min.)
1 lb. cans are sold by L.M.I.
5lb. quantities of various grades are available from
(best source for information, too!)
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