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MMD > Archives > June 1999 > 1999.06.15 > 10Prev  Next

Hot Hide Glue -- Questions & Answers
By Craig Brougher

Hi All,  In response to requests for more information about how to use
hot hide glue for virtually every aspect of player piano rebuilding,
Craig Brougher has written another fine article for Player-Care.

The article approaches the topic from a Question & Answer view point,
wherein Craig poses common questions and then gives detailed answers.

Craig and I both hope that this page will be just the beginning of a
series of pages devoted to Frequently Asked Questions.  Player-Care has
a few FAQ pages already, but with the Internet growing at such a
phenomenal rate, there's hardly time to get "real work" done and still
answer the hundreds of questions that we receive every month.

This web page can be viewed at
The article follows.


John A. Tuttle

 [ Thanks to John and Craig for sharing this article with MMD.
 [ -- Robbie

 - - -

From: (Craig Brougher)
Subject: Hot Hide Glue -- Questions & Answers

    HOT HIDE GLUE -- Questions and Answers
    Written by Craig Brougher

This is a subject that is sorely needed in the field of player piano
rebuilding and every other form of furniture building.  in it, I will
try to answer for you all of the questions you may have about hot
animal hide glue from questions I have received myself.  So first, I
will address the questions dealing with its intrinsic worth as a glue,
to begin with.  If you have another basic kind of question about hot
animal hide glue that we haven't covered, maybe I can add it to this
list.  It seems to keep growing.

Q:  TiteBond, Elmer's, and other white and yellow PVA glues seem to work
just fine.  They are stronger, they apply easier, they are more readily
available, and they will glue a broader array of materials than will
animal glue.

A:  That's wrong on all counts.  Stronger?  Not hardly.  A wood-to-wood
bond, for example, will vary widely with the PVA and modified PVA
glues, depending on the porosity, time of clamping, etc.  Also, once
they have fully dried, their hidden glue joint looks like an old-
fashioned lace, because it must lose a percentage of its water content
it must be under pressure the entire time, since moisture loss results
in adhesive thickness decrease.  That weakens its bond.

Hot hide glue isn't under those constraints at all.  It sets by gelling
momentarily, dependent on temperature and time to set.  From that
point, no clamping is even required, and it just keeps getting tighter
and tighter, a 100%, perfectly conforming airtight joint that will not
leverage apart its own bond, as does PVA glue in unexpected instances.

This is why hot hide glue is so vastly superior to PVA glues in
strength.  Hot hide glue will never set up in one portion of the bond
and remain still wet in another section -- as does PVA glue -- which
negates the theoretical strength of PVA glues completely.  Freshly made
animal hide glue is so much stronger than the wood itself that there is
no comparison.  On the other hand, PVA glue joints are not as strong as
the wood, even though they may take wood with them when broken apart
(which doesn't mean much).  They most certainly are not airtight joints
by their very nature because of the way in which they must evaporate
and absorb moisture into the wood to allow setting to occur.

I am not denigrating PVA glues, by the way.  They are a chemical
marvel, when employed in the things they are designed to do.  They are
called "carpenter's glues" and that is not by happenstance.  So why not
let carpenters buy them for carpenter stuff?  And carpenters who also
build furniture will themselves decide if they can improve on their own
glue or not.

On the other hand, artisans who want the best would not even touch a
factory sample of modified PVA glue because its bond is "elastic".
That means, given a steady pressure, that joint will "creep".  When a
joint creeps, certain parts of the joint "stretches".  As it does that,
other joints must "adjust" as well.  Pretty soon, the chair or rocker
or cabinet starts getting wobbly because its joints are pulling apart.

Chairs, for example, which are repaired using PVA glues last about
1-1/2 years, and then become looser than ever.  Why?  Because the
mortise/tenon or dowel joint was never tight to begin with.  So,
because it continues to shrink about 1-1/2 years, they loosen up.
Now, this is only if the chair is never used.  If used in that time,
it breaks apart much more quickly because the weight on the chair
stretches the still loose dowel joint, and if one joint is stretching,
the others must, too.  One stretched joint puts the pressure on the

On the other hand, hot hide glue margins in a loose dowel joint do not
move at all.  Even when the joint fails, the margins stay as hard as
rock.  So you have radial support for the dowel, even if you don't have
axial support.  That may protect the other joints from following suit.

It is a false premise that slightly flexible joints will be stronger
than hard ones.  Any joint susceptible to "creep" dooms all the other
joints in furniture like chairs, or anything else dependent upon the
stability of its own wood.  So unless each joint is rock hard, no joint
can be safe for very long.  Hot hide glue and epoxy are the repair
glues of choice here, commonly.

Airtightness?  This isn't only important in pneumatics.  It's important
in all quality furniture (You figure it out).  But, in player pianos,
a lacy pattern in a glue joint, times 88 notes, makes for a weak
performance, and an impossible correction.  You have ruined it!

They apply easier?  No way!  When you apply PVA glues, you do so with a
squeeze bottle.  It instantly begins to evaporate and dry, and so does
hot hide glue, even faster.  However, in the same circumstance, you can
reheat the hot hide glue joint with an iron and restore it.  Not so
with the PVA glues.  So if you like squeeze bottles, put the hide glue
in a squeeze bottle.  If it wants to set too quickly, add water, heat,
or both.

You can veneer with hot hide glue.  Not so with PVA, because PVA glue
has no grip when setting, it doesn't spread well, you cannot success-
fully thin it and still get much strength when dry, and its need
to evaporate to set up, would curl the veneer off the surface anyway,
unless you are doing very small inlays and can control wood warpage
completely.  Remember too, that hot animal glue has what is called a
"death grip".  That means, once the parts are contacted together, as
long as their initial press was solid and not allowed to slip, the glue
will act as its own clamp.

Conversely, PVA glues require clamping for 24 hours to attain their
advertised strength.  Since small parts invariably slide when clamped
unless extreme measures are taken, just the instructions on the bottle
itself prove PVA glues to be most difficult to use properly.  Hot hide
glue doesn't require clamps, and by sizing one or both surfaces first,
just dampening a surface and then warming it back up will reactivate
the glue momentarily, which seizes its mated surface quickly and acts
almost like contact cement.  Thus, complex shapes can be followed with
success when experienced in its use.

As far as gluing a wider range of materials, this isn't so, either.
Hot hide glue is so versatile that certain additives allow it to be
used for almost everything.  Its bond is molecular.  It's a chemical
bond primarily, and a mechanical bond, secondarily.  PVA glues bond
only mechanically.  And since they are elastic, PVA glues only work in
areas where there are only momentary shear forces at work.  If shear
forces are continual, PVA glues will creep, slide apart, and break
relatively quickly.

So in player piano work, if you have been unfortunate enough to own a
set of clamped block valves sealed with a cushioned gasket material
like cork, glued together with TiteBond or a similar glue, you will
discover that the pouch boards will have slid back on each of the block
valves, until they begin to leak and disable the player.

Q:  I have rebuilt lots of player pianos using PVA carpenter glues,
and they all played fine.  So what can you say about that?

A:  I am constantly stripping down a lot of actions like that and
restoring them, too.  And I can speak from experience that, without
exception, everything that was glued down with PVA leaked excessively,
or, it was thickly filleted around with so much glue that the parts had
to be re-manufactured, making the original player parts unrestorable,
except by using new wood and extra time that should have been
completely unnecessary.

I also find many parts like pneumatics badly aligned with the piano
actions because the pneumatics had to be clamped overnight to make a
bond.  And even at that, many warped, due to the direct release of
moisture into them from that kind of glue.  In addition, those actions
which were put back with PVA glues were typically mediocre to bad
workmanship all the way around.  Cheat on one thing it seems, and
nothing else really matters that much, either.  So I invariably find
the cheapest materials, worst quality bellows cloth and covers, valve
leather that should have ended up in the trash can, and many necessary
but easily hidden or camouflaged things undone.

"Faithful in little, faithful in much.  Unfaithful in little,
unfaithful in much".  That saying works every time.  There is never an
exception to it.  To the contrary, rebuilds in the 50's and 60's which
used hot hide glue have, without exception, proven to be much more
nicely and conscientiously done, neater, more detailed, and show a
degree of respect for the instrument and its original maker.  And I
feel a degree of respect for that rebuilder, who at least tried to do
his best work.  It makes me feel like there are still honest people in
the world.

Put yourself in the next rebuilder's shoes before you attempt your next
player and ask yourself, "Would I want to know this guy?  Or has he
just made my life miserable, not caring if the instrument survives his
rebuild, or not?  Did he just think of himself, or was he conscientious
enough to regard his instrument highly, and to pass it on in good

Q:  I bought some hot hide glue, tried to use it, but no matter how I
thinned it out, I couldn't get it to stick to anything unless I just
piled it on, and that "hinge-bound" the pneumatics.  I found I could do
a much neater job with PVA glue.

A:  Sounds like the problem you had wasn't of your own making.  There
are grades of hot hide glue that must be specially designed for a very
narrow range of applications.  These are usually the super-strong hide
glues that require special techniques and environments to utilize

The best glues for shop work vary in gram strength from between 130-170
gm.  But there are hide glues that range all the way from 30 gm to 600
gm strengths, and having vastly different characteristics.  Don't buy
glue from anyone who can't tell you what grade and gram strength they
carry.  It may be okay, but you're taking a chance.

Q:  I was told that fish glue is just as good as hot hide glue, just
as strong, and much easier to apply.  What do you think about doing a
player with it?

A:  Fish glue is a "specialty glue" only.  It is not designed to glue
player actions together.  It is mainly used for emulsions, but the pipe
organ industry uses it to get an instant grip between leather and
leather, or leather and cloth.  It allows soft lambskin to be contoured
around corners because of its cold tack properties.

On the other hand, fish glue is very hygroscopic (meaning that it draws
moisture from the air).  Long-term humidity alone can disassemble parts
put together with fish glue, whereas hot hide glue, once fully dry, can
withstand about any amount of humidity without weakening, and over 400
degrees Fahrenheit without softening.

Q:  What do you think about using some of the other glues on the market
today, like Weldwood space age miracle adhesive, or PVC-e glues, like
Sobo, super glues and epoxies?

A:  I think some of these glues are fine for specific jobs.  Super glues
like Hot Stuff, especially, when you have the mild hardener to go with
it, really works wonders with broken action parts.  It makes them much
stronger than the original parts.  It's also good to harden screw holes
and do a variety of wonderful jobs in seconds that used to take hours.

Sobo and Plastic glues (PVC-e glues) are good to glue things that
require an elastic bond, or to materials that hot hide glue in its pure
form without additives isn't able to stick to.  Devcon 5 minute epoxy
is one of the most convenient glues of all, when mixed properly.  I
love it, and use it often, particularly when I need to fill gaps, or
need a bit of an initial tack when I cannot clamp.

On the other hand, some of the most highly advertised space-age glues
aren't any good, period.  So my advice to you is, test it first.  Glues
also can go bad, like the alpha cyanacrylate super glues.  In all,
these glues are "specialty" glues, and not to be used for the general
rebuilding process.

Q:  I used hot hide glue on my first player, and said, "never again".
The pneumatics started falling off the shelves about three weeks later.
That stuff is terrible.

A:  Hot hide glue has what we have called a "death grip".  It begins as
the glue cools and starts its gelling phase.  This setting period is
critical, because within this small window of time, the part cannot be
slid or bumped without ruining it.  The best thing to use is a weight
when gluing pneumatics, and if you don't have weights, then size the
shelf they glue on, first, and then after the sizing coat is moderately
dry, mount the pneumatics without weights.  Clamps will slide the
pneumatics, and instead of assuring a bond, they will more likely
assure disaster.

Another mistake is to use a glue pot that gets the glue too warm; that
means, over 150 degrees F.  This temperature weakens some formulations
of glue considerably.  Other formulations (such as the chrome-tanned
types) it will not hurt.  If glue is applied too slowly, or is too
thick, it will break easily because a large percentage of it was
getting cold while the percentage of water in the glue was too low, so
your latitude to tolerate slow application time is greatly shortened.

Whatever the application, remember that hot hide glue is similar to
solder.  Unless solder flows into a joint and is kept motionless until
it sets, it will become a cold solder joint that looks like it's stuck
until some weeks later when it suddenly just snaps off.  A bad hot hide
glue joint does the same thing, and the joint then can be seen to be

Whenever you glue anything with hot hide glue, be sure the glue is
flowed onto the surface and remains wet while the other piece is
contacted and pressed down.  People who "paint" glue onto a surface,
trying to be meticulous should realize that the trick to a good joint
is their accuracy and quickness of application.  And if they aren't
managing, then to use a bigger brush and add a little water to the
glue; just enough that they have the time they need.  Otherwise, they
must pre-warm the parts they are trying to glue.  For example, put
pneumatic leaves in a cardboard box in the oven at 150 F first.

Q:  I wanted to use hot hide glue on this player, but I'm afraid to
because the first guy used white glue.  I'm afraid it won't stick to

A:  Got a propane torch?  By briskly moving the torch over a solidly
clamped part, you can heat it up to just the right temperature with a
flat nozzle and then blade off most of the white glue without burning
the part.  On pneumatics, you can clamp many of them together and do
the same thing.  Once scraped, resize these edges first with a thin
mixture of hot hide glue and allow to fully dry.  Once you prove that
the glue is sticking and not cracking off, then you can go ahead and
use hot hide glue.

Q:  I can never seem to get the consistency right.  It's either too
thick, or too thin, or something's wrong.  I just have trouble using
a brush, I guess.

A:  Begin with a new pot of glue and put a candy thermometer in the pot
to check temperature.  It shouldn't be over 150 F, ever.  140 degrees F
is about right.  Grab some scrap wood and a brush and try some.  It's
probably going to be too thick.  Add water with an ounce cup.  Try 2 oz
at a time.  Notice the difference it makes.  Practice just a minute
before you start in.  If you're too slow, then get a larger brush.  A
1" natural bristle brush is great for large bellows, and even works for
pneumatics when you're slow.  Otherwise, a 2" brush is better.  But
always use natural bristle.  White china bristle is good because it
doesn't deform much over time, sitting on its bristles.

If you are covering pneumatics, you'll want fairly thin glue.  If you
are mounting them, you will want medium weight.  If you are gluing
felts, you will want thick glue.  Gluing heavy bellows requires a
double gluing of medium weight glue.  That means, you will apply glue
to the edge of the bellows, press down the cloth, then pick it back off
and reglue.  Once covered, you will then wait for it to dry, or at
least set for 2-5 hours, and then iron at a low heat.

Ironing down bellows covers after double gluing greatly increases the
tightness.  But if you fry the glue (it turns white and powdery), you
will have to do it all over again.  So watch for just a few tiny little
wet beads of warmed glue appearing at the edge of the joint as you go
around the bellows.  Take your time.  Use your hand as a temperature
sensor to prevent getting too hot.

Sizing parts first helps the setting grip.  It strengthens it and
speeds it up.  So when you are sure you will not need to re-position
the parts too much, then I recommend sizing first.

Q:  Are you sure about the strength of hot hide glue?  It doesn't seem
very strong, to me.

A:  Oh, it's strong all right.  Even relatively weak hide glue is
stronger than wood.  You might have some old glue, there.  Glue doesn't
have to stink to be old.  If your pot is too high a temperature, or you
are using an aluminum liner to keep it in, or you keep reheating it
every day, or if you leave tin-plated iron throwaway brushes in it,
then it loses its strength fast.  On the other hand, you don't have to
make it fresh every day.  That's wasteful.

If you make a fresh pot and then don't plan to use it in the next day
or two, turn it off.  But if you plan on using it steadily for the next
few days, just leave it plugged in.  Keep it in a glass jar that fits
your heating jacket, with a plastic lid over it, about the size of a
small yogurt cup lid or tennis ball can lid.  If your jar is smaller
than the jacket, cut a ring of Styrofoam that fits snug around the jar
and stands on the rim of the jacket, sealing in the heat.

If you forget to cap it and it dries out, as long as you don't use that
glue for wood to wood strength joints, it's still very useful to glue
covers, pouches, valves, and what-have-you.  But don't use
reconstituted hot hide glue for critical work like gluing down
pneumatics; just to be safe.  Start with a fresh pot of glue for all
wood to wood joints.

Q:  How do you recommend fixing a broken grand piano lid?  Someone said
to use a biscuit jointer and PVA glue.  It is a clean break right
across the center of the lid.

A:  start with two strong, heavy and straight runner supports on a table
or bench crossing the break at right angles.  Don't strip the lid or
remove the finish.  As long as the break is clean, this is the
strongest way to do it.  The first thing you must do is to determine
that the two halves of the lid are flat and true with each other by
shimming the lid to the runners.  You are going to just butt glue the
lid together with no splines or biscuits, but you have to support it
first.  It will be just as strong this way as it was originally.
Biscuits won't strengthen the joint, They just keep the two halves
together if the joint breaks again.  Cleat the runners together now so
they won't be moving with respect to each other.

By using the runners as clamps, you can push the joint together and
keep the two large halves true, just by weighting or gently pressing
the halves down at the break.  So insert large plate screws into the
top edges of the runners where they will meet the front and back of the
lid, with two inches or more clearance.  Shove the curved rear edge of
the lid tight against these two screws to begin with.  Your shims can
be front rail paper punchings.  Start with 4 thick ones placed on each
side of the break on top of both runners, and a corresponding thickness
slipped under the front and back edges.  From there, you will able to
get more exact with straight edges and light reflections.

Cut two wedges about 10" long and about 2-1/2" deep at the ends.  Then
you'll need about 4- 1/4" thick pneumatic leaves or scrap wood to
protect the lid edges from clamp pressure denting.  You will also need
some weight to control the joint.  Spread apart the halves and very
liberally and quickly, spread new hot hide glue on both halves
simultaneously with a large brush, or any way you can do that best.

If the shop is cool, pre-warm the joint first with a heat gun or hair
dryer by insulating below and forming a tunnel for the hot air to be
contained in.  Then apply the glue and close up the joint.  Use a
mallet and tap the bass edges of the lid flush, then immediately drive
the front wedges between the plate screws and the wood scrap
protectors.  This will quickly draw up the joint while still wet.  If
you think the joint cooled, reheat it now until you see the glue
beading and getting nice and wet again, drive in the wedges moderately
snug, and place the weight on top of the lid to assure flatness.

Once the glue has set for several hours, remove the wedges, then the
weight and with a putty knife, roll off the excess glue on top.  The
glue on the bottom will stick to the runners, but the old finish will
prevent it from fastening itself permanently to them until fully dry.
Since the width of the break is almost nothing, the excess glue between
the runners and the lid should be immaterial.

When fully dry, the glue will easily break off the lid finish.  The
excess glue along the break underneath will also break off, and
whatever is left can be dampened and wiped off, as long as it is still
fresh, even though dry.  Now the lid may be stripped and refinished if
desired, and the break should be repaired so well that it is hard to
tell that it was ever broken at all.

Q:  What's the best way to glue down pouches?  I seem to get glue just
under the rim of the hole, and it makes the pouch too stiff.

A:  Pouch glue is thinnest of all.  Most people use the same weight glue
for everything.  That isn't good.  Pouch glue should be like a very
thin sizing mixture.  To tell how thin, drill some large through holes
in scrap wood with a forstner bit and try laying down pouches on them.

Dip them as you go with a home-made dipping tool.  That's just
basically a washer or disk as large as the pouch circle with another
smaller washer or disk glued to it to create the overall dip you want,
and a handle to control it with.  Do not dip the pouches after they
have been placed and dry.  Pouch leather does stretch, very true, but
it also returns back fairly close to its original dimensions after
awhile.  That is why pouches appear to "shrink".  They were dipped with
a stretch.

Q:  I seem to make a mess out of pneumatics.  They are tight and
straight, but I can't keep my sticky fingers off the new covers.

A:  I would also doubt then that they are tight and straight.  The only
correctly covered pneumatic is a clean one.  That is the proof that the
person covering knew the correct way to cover, and so the chances of
those covers being tight and the leaves true are much better than when
covers are stippled with gluey fingers.

When glue is too thick, too thin, the brush too large or too small,
or the method is clumsy and the lighting poor, then problems occur.
Instead of belaboring the subject, let me suggest a covering jig now
made by the Player Piano Co. in Wichita, KS.  It is designed from one
I built for them years ago, and allows the greenest novice to start
covering pneumatics perfectly after just a few tries.

However, do not use their plastic glue for any pneumatic.  Pneumatics
need good support all the way around.  That means, you cannot do it
with a hinge, alone.  And were you to use their hinge circles, which
are simply adhesive tapes, and then cover the pneumatics with plastic
glue, you really have no support at all, to speak of.  Don't trust
shortcuts.  They are usually just shortcuts to disaster.  If you have
to hinge a set of pneumatics, use canvas and hot hide glue, with strips
of wax paper in-between. .

Q:  I have been told that Hot hide glue will not stick to nylon cloth or
any synthetic sealant, like polyurethane.  But you say that you use
nylon cloth and always use hot hide glue.  So how do you do it?

A:  I can't answer for every form of glue and every nylon material there
is to use, so let me say that whenever you buy materials, test them
first.  They may not work well.  But the nylon/polyurethane pneumatic
cloth from American Piano Supply Co. is the best there is, in my
opinion, and it glues perfectly to the sealant side with hot hide glue.

I have, in the past, received different brands of nylon cloth, and some
did not work well at all with any glue.  I have seen a set of
pneumatics literally fall open as though they had never been glued, and
they had been done with PVC-e glue and a particular brand of bright red
pneumatic cloth with a white backing (this was many years ago).  If you
find that your cloth has a release agent on it that prevents gluing,
you could try wiping it down with a solvent like lacquer thinner,
first.  The basic principle is always, "Try it first.  Don't just
blindly trust whatever you buy to work correctly.  Check it out."

Written by Craig Brougher
Phone No: 816-254-1693

(Message sent Tue 15 Jun 1999, 22:57:13 GMT, from time zone GMT-0400.)

Key Words in Subject:  Answers, Glue, Hide, Hot, Questions

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