Re: Boil Testing Glues and Plywood
Hi Nels
From David Carnell's studies "glue lines are
significant moisture barriers", even better than
epoxy. Moisture might get trapped in the plywood.
see:
http://tinylink.com/?qMbHBZPjUJ
Mat
From David Carnell's studies "glue lines are
significant moisture barriers", even better than
epoxy. Moisture might get trapped in the plywood.
see:
http://tinylink.com/?qMbHBZPjUJ
Mat
--- Inbolger@yahoogroups.com, "Derek Waters" <dgw@d...> wrote:
observation and one question. The observation is that if the plywood
is totally encapsulated how would the there be exposure of the glue
lines to the elements? This would indicate that epoxy is not really a
moisture barrier as I had supposed.
The question then arises - Is the test to deterimine water proofness
or adhesion and shear strength? Of course if you boil tested epoxy
glue lines they would fail miserably every time.
Some years ago I was told that all plywood manufactured in Canada had
the same glue and the only difference was in the cores themselves.
But of course these days almost all the decent plywood is imported
and we export all our best stuff.
I am not trying to be controversial here but more than a little
confused about the concerns for waterproof glues when using epoxy and
glass. Actually I am more concerned on what is going to happen to the
wood if moisture builds up - not so much the glue. Or even more than
that - concerned about inferior inner plys themselves to begin with.
Thanks, Nels
> Hi Nelsas the
>
> Remove the adhesive from a sheet of plywood on the other hand and
> you have sheets of veneer; the epoxy coated boat would be as strong
> outer layer of the ply, with the rest as cargo :)the
>
> Boil-testing adhesives has a good scientific pedigree. Usually when
> subject is raised some humorist comments about not sailing inboiling water.
> There is a demonstrable correlation between the results of exposureto the
> elements over a long period and the results in the short term ofrepeated
> cycles between wet and dry.Okay, that makes sense if the science is sound. That leads me to one
observation and one question. The observation is that if the plywood
is totally encapsulated how would the there be exposure of the glue
lines to the elements? This would indicate that epoxy is not really a
moisture barrier as I had supposed.
The question then arises - Is the test to deterimine water proofness
or adhesion and shear strength? Of course if you boil tested epoxy
glue lines they would fail miserably every time.
Some years ago I was told that all plywood manufactured in Canada had
the same glue and the only difference was in the cores themselves.
But of course these days almost all the decent plywood is imported
and we export all our best stuff.
I am not trying to be controversial here but more than a little
confused about the concerns for waterproof glues when using epoxy and
glass. Actually I am more concerned on what is going to happen to the
wood if moisture builds up - not so much the glue. Or even more than
that - concerned about inferior inner plys themselves to begin with.
Thanks, Nels
Hi Nels
You are right - strip canoe building does not place serious demands on the
adhesive used between the strips. The final canoe is really a woodcored
'glass and resin canoe. Were the glue between the strips to magically
disappear the hull would scarcely be affected since the strips retain their
natural strength along the grain and the 'glass matrix gives the sectional
strength. Remove the adhesive from a sheet of plywood on the other hand and
you have sheets of veneer; the epoxy coated boat would be as strong as the
outer layer of the ply, with the rest as cargo :)
Boil-testing adhesives has a good scientific pedigree. Usually when the
subject is raised some humorist comments about not sailing in boiling water.
There is a demonstrable correlation between the results of exposure to the
elements over a long period and the results in the short term of repeated
cycles between wet and dry. It's my understanding that raising the
temperature supplies extra energy and hastens the breakdown of the materials
involved. The USDA FPL Wood Handbook has some information on the merits of
various adhesives and the ASTM tests for plywood It is available online,
IIRC
cheers
Derek
You are right - strip canoe building does not place serious demands on the
adhesive used between the strips. The final canoe is really a woodcored
'glass and resin canoe. Were the glue between the strips to magically
disappear the hull would scarcely be affected since the strips retain their
natural strength along the grain and the 'glass matrix gives the sectional
strength. Remove the adhesive from a sheet of plywood on the other hand and
you have sheets of veneer; the epoxy coated boat would be as strong as the
outer layer of the ply, with the rest as cargo :)
Boil-testing adhesives has a good scientific pedigree. Usually when the
subject is raised some humorist comments about not sailing in boiling water.
There is a demonstrable correlation between the results of exposure to the
elements over a long period and the results in the short term of repeated
cycles between wet and dry. It's my understanding that raising the
temperature supplies extra energy and hastens the breakdown of the materials
involved. The USDA FPL Wood Handbook has some information on the merits of
various adhesives and the ASTM tests for plywood It is available online,
IIRC
cheers
Derek
Nels,
The only time I perform a boil & freeze test is on a type or brand of plywood that I've not used before. Typically, if it is standards rated I don't worrk about the suitability.
The goal, mine at least, is to submit the plywood (or adhesive for that matter) to testing beyond what would be typical usage. I place a 6x4 inch piece in boiling water for 1/2 hour, then transfer the wood to the freezer for 24 hours. I repeat this process for 5 days and check for any signs of delamination.
I also may leave a couple of test pieces exposed to the natural elements on the patio for several months, again looking for delamination.
Others may use dishwasher tests, long term submersion, etc.. I think the goal for all such testing is the same. The structural strength of a piece is evident by touch and sight, the internal bonding of the plies needs some sort of testing process.
James
[Non-text portions of this message have been removed]
The only time I perform a boil & freeze test is on a type or brand of plywood that I've not used before. Typically, if it is standards rated I don't worrk about the suitability.
The goal, mine at least, is to submit the plywood (or adhesive for that matter) to testing beyond what would be typical usage. I place a 6x4 inch piece in boiling water for 1/2 hour, then transfer the wood to the freezer for 24 hours. I repeat this process for 5 days and check for any signs of delamination.
I also may leave a couple of test pieces exposed to the natural elements on the patio for several months, again looking for delamination.
Others may use dishwasher tests, long term submersion, etc.. I think the goal for all such testing is the same. The structural strength of a piece is evident by touch and sight, the internal bonding of the plies needs some sort of testing process.
James
[Non-text portions of this message have been removed]
I have had some experience in strip building canoes and have known
people to use all kinds of glues, even "carpenters glue" for joining
the strips together. After stripping and fairing the canoes are
usually empregnated with epoxy as a base coat and fiberglassed. Some
of these canoes are 20 -25 years old and still completely sealed. And
I was never made aware of anyboil testing of the glued strips.
So I am wondering why it is so critical that plywood has to pass such
rigorous boil testing and dishwasher testing etc? Is it because if
boat are left in the water a certain length of time that water seeps
through the glass and epoxy laminates and in through the outer layer
of ply and delaminates at the glue line?
I was under the impression that the epoxy and glass sealed out water
unless the protective skin was damaged in some way and even then it
was the wood that suffered more than the gluelines.
Is the boild test a legitimate test of water resistance or somebody's
idea of a joke and nobody has caught on yet?
If one is simply day sailing from a trailer is it still so critical
to pay exorbinate prices for plywood that claims to pass boil testing?
Cheers, Nels
people to use all kinds of glues, even "carpenters glue" for joining
the strips together. After stripping and fairing the canoes are
usually empregnated with epoxy as a base coat and fiberglassed. Some
of these canoes are 20 -25 years old and still completely sealed. And
I was never made aware of anyboil testing of the glued strips.
So I am wondering why it is so critical that plywood has to pass such
rigorous boil testing and dishwasher testing etc? Is it because if
boat are left in the water a certain length of time that water seeps
through the glass and epoxy laminates and in through the outer layer
of ply and delaminates at the glue line?
I was under the impression that the epoxy and glass sealed out water
unless the protective skin was damaged in some way and even then it
was the wood that suffered more than the gluelines.
Is the boild test a legitimate test of water resistance or somebody's
idea of a joke and nobody has caught on yet?
If one is simply day sailing from a trailer is it still so critical
to pay exorbinate prices for plywood that claims to pass boil testing?
Cheers, Nels