Hello,  Gorilla glue is actually not new, just the marketing of it
is new.  Dow Chemical Co. made an expanding urethane adhesive for years
and discontinued it, probably for good reasons.  It was difficult to
work with and you could never use more than a small portion of the tube
before it hardened.  They probably got plenty of complaints from people
who ruined just about everything with it.

Twenty years later, I guess we are ready for such a product as everyone
is used to products that are hyped to death and perform badly for the
suggested applications.  So here comes Gorilla glue which is marketed
as the one glue you need for everything.  I miss Dow urethane because
it worked for certain applications and came in small tubes of which you
only had to throw out about 70% on average.  It stuck better to metals
and plastics than Gorilla glue.

The main problem with Gorilla, other than the mess it makes, is that
it creeps over time.  If there is tension in the joint, it is likely to
fail over time.  It may be fine in non-critical static situations but
the joint may fail if there is constant tension.  I would not recommend
it for piano bridges especially since it is not easy to remove when you
want to remove it.  If you need to remove and repair the soundboard,
you may be out of luck.  Heat will soften it but you may need to first
heat the wood to the point of destruction.

I like the tropical hardwood "Purple Heart" and make many things out of
it.  It is one of the most difficult woods to glue to due a high resin
content.  Gorilla was recommended by a friendly hardware store employee
when it first was introduced.  It was touted as the glue for everything.

I glued a counter top together with it and today it is a mess.  The
carefully sanded wood is uneven at the joints and the couple of improper
joints (mismatched grain direction) have come apart completely.  Besides
creeping, the glue is actually not that strong.  It is a rather flimsy
plastic foam when cured.  It seems strong but that is just because it
is stronger than your ability to test it with your hands.  I have not
done so but I would guess that a proper test will reveal that Gorilla
is really not that great.

Since the failure with the Gorilla glue on the Purple Heart counter,
I have used epoxy exclusively for this wood and have not had a single
failure.  I use an epoxy specifically formulated for resinous tropical
hardwoods.  It is used on multi-million dollar yachts and has been
tested for years.  I have made butt joints in Purple Heart wood which
should ideally have been doweled or splinted, and they have not come
apart or crept as they would have with Gorilla.

If you really want it together forever, use the proper epoxy and the
recommended surface preparation.  If you like to use products that are
advertised on TV, use Gorilla glue.

Best regards,
Spencer Chase