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ARTICLE: The Truth About Polyurethane Glue
In article ,
(J T) wrote:
Some
interesting info.
Thanks Jay-oh-ay-tee; I did find it interesting as it confirmed what
I've suspected through my own uses.
Curious that Gorilla Glue hasn't done scientific testing on what the
founder claims is the glue's strength strength:
Some polyurethane glues advertise themselves as "super strong" and "the
toughest glue on planet Earth." Other polyurethane glues don't make any
claims about glue strength on the bottle. What gives? Frankly, glue
manufacturers seem divided on this issue.
Dale Zimmerman, a technical specialist with Franklin International, which
manufactures Titebond Polyurethane Glue, says that his company's tests don't
show that polyurethane glue is any stronger than yellow glue. Here's how they
tested the adhesives: They glued together 1"-square blocks of hard maple
using a long grain-to-long grain joint -- the strongest type of glue joint
for wood. Then they attempted to break the blocks apart by testing the
joint's shear strength, which basically means they tried to break the bond by
pushing one block up while pushing the other block down.
And what did they find? Zimmerman says that the joints made by the
polyurethane glue failed around 3,510 pounds per square inch (psi) of
pressure. Franklin's Titebond, a popular yellow glue, failed at 3,600 psi.
And Titebond II, their exterior-grade outdoor glue, failed at 3,750 psi.
"Polyurethane glues stick well and hold odd materials, but they generally
aren't stronger than yellow glues," Zimmerman says. "Yellow glue makes a bond
that is stronger than the wood. So while the polyurethane glue might actually
be stronger, it doesn't matter because the wood will always fail first. It's
not a stronger joint."
Other glue manufacturers disagree. Mark Singer, the founder of Gorilla Glue,
says that polyurethane glue is actually stronger than yellow glue when you
use it in types of joints other than the one that Franklin International
tested. Franklin, he says, used a long grain-to-long grain joint, and that's
a joint where traditional yellow glues already excel. Singer says that the
real strength of polyurethane glues is in an end grain-to-end grain joint or
an end grain-to-long grain joint, which are two joints where yellow glues
have always been lacking.
"Shear strength is not polyurethane glue's strongest feature," he says. "In
end grain-to-end grain the stuff is incredible. It far outperforms (yellow
glues) in end grain. If you coat both surfaces with polyurethane glue, I've
seen it (the glue) migrate 2" into wood."
Singer says his company hasn't actually tested this joint scientifically, but
he says he's seen tests from Europe and in the United States that confirm
this statement.
--
Owen Lowe and his Fly-by-Night Copper Company
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