Hide Glue - Working Out for You?

[bandit571]

Hide glue?  
  never touch the stuff

[Handplanesandmore]

OBG is better than hide glue in terms of convenience but more expensive. I use OBG only when the glue up is complex (long working time) or when I might need to undo the assembly if it goes wrong. Roughly 80% yellow/white glue; 20% OBG. OBG matches the dark wood color better than yellow glue.

Put it in the fridge and it can last long beyond the expiry date by a year or so.

Simon

[adamcherubini]

I use it sometimes and would like to use it more often.  I have a glue pot and ganuals for homemade and a bottle of Old Brown Glue in the fridge.

Biggest reason I don't use it more is time.  If I am in the shop 30min here and there its more difficult to heat up and use than a botte of titebond.

If I have the time it works better with many finishes, cleans up easy and can be rubbed, and creeps less pva.  So yeah I like it

In my mind all glues have a place pva, "super glue", epoxy in different flavors and yes hide glue.  Polyurethane even has a place as a construction adhesive.  Its like having different saws to do different jobs.

Not arguing. I found hide glued saved me time, when I could only get in the shop for so long. Like evenings. I'd come home from work, turn on the glue pot, have dinner, then work after dinner till bed time.  Hot hide glue allowed me to work without clamps and set up/gelled fast enough that I could work on something with lots of pieces continuously. I felt it was like Lego woodworking.

[Handplanesandmore]

Unlike hide glue, OBG is not to be used for rubbed joints.
Simon

[Tony Z]

In a recent "Lost Arts" blog, there was a reference to "cross-linked" hide glue. Can someone shed some light on what it is?

[Alan S]

In a recent "Lost Arts" blog, there was a reference to "cross-linked" hide glue.  Can someone shed some light on what it is?

There are various things you can add to hide glue to make it waterproof.  The glue is made of long molecules that tangle and stick to one another, but these additives actually bond molecules together, linking them across chains.  This is useful, but also provides a more limited pot time, impedes cleanup, and makes the glue irreversible, removing some of the usual benefits of hide glue.

A search for "waterproof hide glue recipe" shows that the additive mentioned most often is aluminum sulfate.

(As far as I know, all glues have such long molecules. They happen to be proteins in hide glue.)

[Tony Z]

There are various things you can add to hide glue to make it waterproof.  The glue is made of long molecules that tangle and stick to one another, but these additives actually bond molecules together, linking them across chains.  This is useful, but also provides a more limited pot time, impedes cleanup, and makes the glue irreversible, removing some of the usual benefits of hide glue.

A search for "waterproof hide glue recipe" shows that the additive mentioned most often is aluminum sulfate.

(As far as I know, all glues have such long molecules.  They happen to be proteins in hide glue.)

Thanks Alan-cross linking woud seem to negate the positives of using hide glue.

[adamcherubini]

I may have my science wrong, but I think gram strength is proportionate to molecular weight of hide glue. Higher the gram weight, the higher the strength. I think as you heat and reheat hide glue, you break down the molecules, making the glue weaker.

Pretty sure all hide glue cross links. Cross linking long molecules makes the glue stiff. PVA is strong but not stiff. I assumed low MW glue was also not cross linked and reversed easier, had longer open time, slower cure, and more forgiving.

But all that is based on my use, not science, so I may be completely wrong.

[Jim Waldron]

I may have my science wrong, but I think gram strength is proportionate to molecular weight of hide glue. Higher the gram weight, the higher the strength. I think as you heat and reheat hide glue, you break down the molecules, making the glue weaker.

Pretty sure all hide glue cross links. Cross linking long molecules makes the glue stiff. PVA is strong but not stiff. I assumed low MW glue was also not cross linked and reversed easier, had longer open time, slower cure, and more forgiving.

But all that is based on my use, not science, so I may be completely wrong.

I, with my old chemistry degree, can confirm that you are, in fact, completely wrong, just as you feared.  


Hide glue is primarily very long chain protein molecules in ethanol solution/suspension when applied.  As the alcohol evaporates, the long chain molecules entangle and parts of the molecules are attracted to each other by "electrostatic" forces, more formally known as hydrogen bonding.  Hydrogen bonding is a weak force and does not represent cross-linking.  PVA behaves in a rather similar way, but with a lot more hydrogen bonding than hide glue.  That accounts for the fact that heat and moisture will disrupt the hydrogen bonding and 'mobilize' the entangles long chain molecules of hide glue, while PVA is much more resistant and can't be considered reversible.  (Over a longer time frame, heat and moisture will degrade PVA, as we all know, causing joint failure when we don't want it.  It's just way too slow to rely on the effect to make repairs.)  

Cross-linking, on the other hand, are based on chemical reactions forming far stonger bonds.  Here we're talking about epoxy, polyurethane, polyesters, uv-curing acrylics, and so on.  Very different critters.  

While we are generally nice people, we chemists tend to frown when civilians attempt to "speak chemistry."  

[Handplanesandmore]

While we are generally nice people, we chemists tend to frown when civilians attempt to "speak chemistry."  

Not much different than those of us when we hear someone insisting that a proven product or method does not work (for them) just because they tried it (a few times?) and it did not work.

Simon