I'm wondering if someone knows the actual numbers on glue
strength? (i.e., strength per unit of surface)
I'm talking about the plastic glue (yellow or white -- I
think it's vynil-based), assuming that it is used to glue
two pieces of very-flat very-clean along-the-grain wood
surfaces, with no gap between the surfaces of more than
1/200" or so. At least typical values, or worst-case
values (if it depends on the wood, or on the angle of
the surface with respect to the grain, etc.)
A google search on this newsgroup returns nothing; the
specs of the glue (both on its label and on Lepage's web
site) only include the catchy advertising phrase "bonds
with 2 tons of strength" (GOD, such idiots!! Only for
that I shouldn't buy anything from them!!! :-( such
flashbacks of infomertials advertising crap), so I'm at
Anyway, I'll be grateful for any info!
The LMI catalog had a short note on glue
strength a few years back. I cwn't even
begin to recall the numbers but I can
say this much.
* Shelf life will improve if kept in the
* Shelf life is much shorter than you
* LMI offers a yellow glue with about
double the strength of off-the-shelf
yellow glue. The price is much higher
and when kept cool the shelf life is only
about six months.
* Yellow glue is non gap filling. The
strength comes from infusing the pores
of the wood. Therefore the wood needs
a smooth finish but not burnished as this
will inhibit absorption.
* You are correct on a gap of 1/200th inch.
* Clamping pressures are much lower
than most every woodworker uses. Too
much pressure will result in a starved
* A perfect joint is much more important
than one mught suspect. Never clamp
tight to close a joint. Some sections of
the joint will be starved, other just right,
and other gap filled. Take the time to
get the joint right.
*Regular yellow glue (A.R.G.?) is usually
stronger than the wood being joined.
That about exhausts my knowledge.
Hope I was of some help.
The jury is still out on this one as it has not been prooven either way.
Apparently many people that clamp too hard are trying to close a gap and as
indicated, yellow glues do not fill gaps well. I have never had a joint
fail whether I clamped agressively or not. I choose moderate clamping
Not so sure I agree with the "starved joint" syndrome, merely from the
application of "too much" clamping pressure. Damaged wood fibers can
result from behemoth pressures, but more likely a "starved" joint is due
to insufficient glue applied BEFORE clamping the joint, as opposed to
the pressure of the clamping being the culprit.
If you apply clamping pressure immediately and excessively, you will squeeze
so much out that you can actually break on the glue line after cure,
especially on woods like hard maple which don't soak much. It's NOT a myth
to an Industrial Arts teacher who's seen what teenage males can do to pipe
I was interested so I went down to the shop and took a 12" long X 10" wide
piece of 13/16" soft maple. I ripped it in half and jointed the dges. I
used Lee Valley glue and rubbed the two edges together to make sure that I
had a joint that was evenly coated. I took 3 pipe clamps and used a pipe
wrench on the handles. The clamps left very nice depressions in the outside
of the boards.
I let the glue cure overnight and put the piece in my vise. I used a
ribber mallet and beat the board until it finally broke. It did not break
along the glue joint. One sample does not prove the issue but I was not able
to produce a starved glue joint even with 1 clamp every 5 inches or so (1
clamp 1" in from each and and one clamp in the middle).
A more scientific experiment would involve using a hydraulic press on
small (1" X 1") samples.
Soft maple is more porous that other woods. Hardwoods with little or no
surface texture don't glue as well as woods like pine and mahogany. Also, 1
inch samples are not a great test because the short length of straight grain
doesn't offer the board as much support and it will be more likely to split
along the grain lines.
WE would occasionally test glue strength by gluing up 3 or 4 strips into a
top. The strips were 3 or 4 inches wide and 12 to 24 inches long. We then
would put a strip at each edge raising it up off the bench and hit the
center of the board until it split. Sometimes the glue joints failed if it
was too cold in the shop when we glued it up.
There are a lot of variables to an objective test.
The starved glue joint is a myth. The important part of the glue is the
part that soaks into the wood. I suppose if you could squeeze any
excess glue out before it had a chance to soak in a significant amount
maybe you could "starve" the joint. At a normal working pace, plenty of
glue gets into the wood and the thicker the layer between the two pieces
of wood, the weaker the joint. IMHO.
David Chamberlain wrote:
From all the research that I have read, the strength of the joint is
not directly proportional to the clamp pressure applied. Certainly
using a pipe wrench to tighten a clamp is overkill.
Normal hand pressure (or even less) is probably best if a nice thin
coat of glue is applied to both surfaces.
OTOH, I have not mastered this either and learn with every new project.
On Sun, 7 Nov 2004 16:41:21 -0500, "David Chamberlain"
Attached is the text of message from Franklin - makers of titebond.
This msg was originally posted to this forum and am sorry i can't
credit the original poster.
Response from Frnklain/Titebond rep re:Calmping Pressure
After our discussion here, I wrote to technical support at Titebond
regarding our discussion of clamp pressure. I got a next day reply
from a very knowledgeable and helpful gentleman, Mr. Zimmerman. I'm
posting it here.
I am writing in response to your question about clamp pressure.
First, your calculation and understanding is correct. If you wanted
to produce 200 psi over an area 12" x 12", you would need 28,800
pounds of force. On the other hand, it is not clear whether you
often, or ever, fell short of the actual, required clamp pressure.
The actual required clamp pressure for any bond involving a wood glue
is a combination of the small amount of pressure required to squeeze
the glue into a thin, consistent layer, and the pressure necessary the
compensate for any distortion or lack of fit in the wood stock being
used. That means when the surfaces of the pieces being joined are
true, and there is no gap between the pieces when they are dry fit,
very little pressure is required. If, however, the same assembly is
being made using pieces which are bowed, twisted or ill-fitted, the
required pressure is much greater, and is largely the pressure
required to straighten the wood and pull it into position. Thus, the
actual required pressure for a bond also reflects the thickness, or
fight, of the wood involved, with much more pressure obviously
required to straighten a very thick piece of maple or oak than to
straighten a thinner piece of the same species.
In many applications, then, pressure, serves to compensate for some
lack of diligence in wood preparation. That being the case, good wood
preparation lessens the need for, or dependence on, pressure. In the
case of our literature, the high suggested pressures reflect the fact
that those individuals being addressed include those who, at least on
occasion, are trying to bond thick, poorly fitted pieces of wood, and
for those readers, the high, suggested values are, indeed, necessary.
Finally, because the bond strength produced in a joint is the result
of the entanglement of the glue particles which have been drawn into
the pores and anchored to the wood on the two sides of the joint,
there is rarely any concern for applying so much pressure that the
glue is all squeezed out.
In fact, the bond strength achieved increases as the bondline or layer
of glue becomes thinner. Given that fact, there are only two
situations in which high pressures may be counterproductive. First,
there is always a concern that the pores of wood at the bonding
surfaces not be crushed, and that is the reason that our listed
pressures are lower for the softer woods. The second situation deals
with bonds involving end grain or other open grain. There the concern
is that the open grain is prone to suck up a large amount of glue and,
if that thirst has not been quenched before clamping, that excessive
absorption of glue may result in a starved, and weak joint. Because
most bonds involve face or edge grain which is relatively straight,
that particular risk is rarely a concern.
I hope this response is helpful, and ask that you feel free to write
again or to call me at 1-800-###-#### if I can be of any further
What a pleasant way to say "Our glue will hold with little or no
clamping pressure if you guys would get your shit together and make
tight joints with straight wood... lol
Thanks for posting that... it is good info and a reminder to not blame
the glue for my poor workmanship and to be more diligent in learning
Actually, what he said was quite different and positive not negative,
"Our glue will hold if you bring the joints together, either with
perfect jointing which then requires little pressure or with imperfect
jointing which requires whatever pressure is needed to squeeze glue
out along the entire length of the joint."
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