ATTN: Chemist

[Dave Fleming]

I am a bit confused, nothing new there eh?
Consensus in these forums is that Epoxy and White Oak laminations are a no-no as I read it.
Now I happen to peruse the Cayuga Boatworks site and they describe a restoration using just such a combination.
What gives? It this anti-white oak epoxy tale just that or is there real evidence that the two do no go well together?
I am NOT here to debate but to learn about this as my experiences with epoxies is relatively limited. Teak laminations for interior use with Cold Cure out of BC, Canada and West System with Ash for deck beams.
Thanks
dave
http://www.cayugawoodenboatworks.com...r/default.html

[Mirelle]

I have seen, with my own eyes, a set of laminated English oak deck beams, for a Lyle Hess 24 footer, made with epoxy, which failed whilst the boat was still in the shed. This was in a wooden boat specialist yard which known for its high standard of work; there were certainly no issues of temperature, freshness of ingredients, cleanliness, etc., to explain it.

That's the only fact that I can adduce, but you are welcome to it.

[thechemist]

Well.....this is certainly not a trivial question.

The word "epoxy" is a generality, describing only one half of a thermosetting resin system... the epoxide group [two carbons and an oxygen in a three-membered ring], the combination attached to various other things....curing agents of various sorts, made from wood or vegetable-derived resins or petrochemical-derived resins, this last distinction having largely to do with the average molecular weight of the ingredients and thus the spacing between molecular cross links....perhaps how much plasticizers or volatile diluents such as benzyl alcohol or butyl benzyl phthalate might have been added...

There is no epoxy resin in a cured epoxy resin. Epoxy resin is the generality name for a variety of synthetic materials with one or more epoxide groups grafted onto them. The solid material formed by reacting an epoxy resin with its curing agent, normally containing nitrogen compounds called amines, is also called an epoxy resin. The word resin itself may mean a liquid or a solid.

You know sometimes words have two meanings......

Cured epoxy resins would, technically , be called either a beta-hydroxy amine or a beta-amino alcohol. If people had been more rigorous fifty years ago, the cured stuff might have been called a beta resin, but it did not happen.

Depending on the formulation, a mixed [or cured] epoxy resin/curing agent system may or may not be capable of dissolving the oils in oily hardwoods. If it can, the chances of adhesion to oily hardwoods are obviously better.

Depending on the formulation, a mixed [or cured] epoxy resin/curing agent system may or may not be capable of chemically reacting with itself and curing on woods containing an excess of acids or alkaline chemicals. [This is similar to some people being allergic to some things] If it can, the chances of bonding to such woods are obviously better.

Depending on how thoroughly the A and B components were mixed to attain a molecular degree of intimacy, so all the little A and B things were perfectly interleaved, and one did not end up scraping out some unmixed part B from the bottom of the mixing container while applying, the chances of good adhesion are obviously better.

Depending on how much mechanical stress was built-in to the glue joint by stressing the elements with great clamping force while gluing, the frozen-in stresses may exceed the shear [cleavage] strength of the wood. Woods generally are quite weak in cleavage [they split readily] and are strong in tension. If the wood pieces were assembled and fit with no force applied, and the adhesive cured with the pieces resting gently against each other, and steam-bent pieces were equilibrated as necesary so they had mechanical stability [no memory] and did not warp after fabrication , and the differential coefficients of thermal and hydrolytic expansion of the pieces being glued were well-matched so there was little enough differential expansion in the glue-line after gluing and ageing in the weather, and what glue-line stress there was, the adhesive had sufficient flexibility as to be capable of absorbing it due to the combination of adequate flexibility and adequate glue-line thickness, the chances of bonding to such woods are obviously better.

Every producer in the consumer marketplace will tell you their product(s) is good for everything. Everyone in the military marketplace does similarly, or so it sounds sometimes. Half of everything you hear is a lie in some specific circumstance, and might be true in some other specific circumstance. This is why military customers do real-world tests. Does the bullet actually penetrate the armor plate, and within what range of angle? Can an infrared sight see the tank in the bushes when the infrared-absorbing paint is all over the tank? How about when it rains, and the infrared-absorbing paint now behaves differently because it got wet? [oooops.....sometimes one gets surprises in the field trials no one thought of on the drawing board.]

Even wood is different, form one piece to another. Some pieces of oak are more acidic than others. Some pieces of oak may warp after gluing, or expand differently. Some glues may be very inflexible. Some glues may be very sensitive to residual wood acids. Some glues may only tolerate a small variation in the mixing ratio. Some glues may show large changes in their sensitivity to acids when a small variation in the mixing ratio ocurrs. Some glues may show little variation in their properties or sensitivities when mixed accidently a little off-ratio.

The human error of failing to zero a scale when placing a mixing cup thereupon, or zeroing the scale for a clean, dry mixing container, and then weighing out a batch using the old mixing container with a wet gooey residue of the previous batch, this sort of thing can be an invisible error that leads to failure.

Talk to individual manufacturers, ask them how tolerant their adhesives are of mixing off-ratio, how tolerant of oils or acids in the wood, and so forth. Then get some of this-and-that and try them. Do not clamp joints tightly. Remember to mix in one container, transfer to a second, and mix all over again with a new stirring tool. Good luck.

[Dave Fleming]

Chemist, with utmost respect....HUH?

Lets us get hypothetical for sake of discussion only.
All things being equal ie:
the white oak is at about 12% moisture content.
the surfaces are as planed from a floor mounted machine such as a Buss/ Oliver/Moak.
the (2) parts of the compound, the hardener and the epoxy resin are mixed according to weight not cup measure in virgin cups.
the mix is vigerous and no bits are left on the cup walls.
the mixture is applied in an atmosphere, clean, dry and temp in the low 70's or high 60's "F" not "C".
the pieces of white oak are coated as evenly as is possible and brought together with clamping pressure applied evenly.
no super squeeze the clamp up is done with care to prevent that.
temperature is maintained in the glue area and no drafts are permitted.
after 24 hours in this situation the clamped up lamination is unclamped and made ready for the next step in the fabrication process.
To the best of your knowledge and experience will this be successful?
Will white oak and epoxy work as a structural marine member?

[NormMessinger]

I understand the chemist to be saying that epoxy will not stick anything together.

On the other hand he probably refers to the concrete ramps where airplanes park as tarmac and to flight data recorders as black boxes. What ever....

Asking the respective suppliers of epoxy products is relevant, however.

--N rm

[thechemist]

Depending on the particular glue involved, its mechanical properties [coefficients of expansion with heat or humidity ...these will vary with age from the initial conditions], its inherent sensitivity to developing a proper cure in the presence of whatever residual acids, oils or strange chemicals might be in the oak and capable of migrating into the liquid glue before it turns into a solid, and perhaps other invisible demons and imps and evil spirits that seem to get into things sometimes, sure, it will probably work.

On the other hand, it may not.

I assume whatever you are using , the manufacturer says it is fully cured in 24 hours. Fine, go with that. Laminate up a test stack, and run it through the planer and chew down all four sides. See if the cutting stress and vibration causes the glue joints to fail. If it does, try a more flexible glue. There are many different epoxies available to you. If you doubt flexibility is an issue, along with various glues of different flexibilities, try some 3M5200. I am not recommending it for laminating an oak piece for your boat, but I think you will find it takes the vibration and mechanical shock of the planer better than a really stiff epoxy. You will need to allow plenty of time for it to cure...maybe a week, I dunno.....

Measure with a digital vernier caliper the dimensions of a three-by-three piece of oak, or even the width of a few pieces. Put them in the oven, warm to a hundred and thirty fahrenheit, measure, let cool down and see if it comes back to original size. See what the expansion in width of several different but apparently-identical pieces of oak is. You will be surprised.

Just do a few experiments. I could tell you what to think but I beleive people are smarter when they see something for themselves as opposed to being told what to see. It is an excellent beginning that you asked the question in the first place, seeing contrary data. Surely, everyone cannot be right.

If you do an experiment and the glue joint fails, then you know THAT glue on THAT piece of wood failed. Sand off THOSE surfaces and try the same wood pieces with a different glue. Odds are some will work better than others.

[Dave Fleming]

Cnemist, I ain't glueing up anything.
Just was looking at that web site, see URL in first post and got curious about them using WEST stuff with white oak.
I agree 'emperical' is probably the most cautious route to take.
I recall the failures when yards started using Resorcinol Resin, the red/deep maroon stuff, and things started to unravel.
Then the folks tried reading the directions and stoped approaching the stuff as if they were using Weldwood Plastic Resin glue.
Seems to have made a difference in the finished product, if ya folla?

[This message has been edited by Dave Fleming (edited 09-30-2001).]

[George Roberts]

A properly done epoxy/white oak bond has a shear strength of about 1900psi (for the epoxy I use). Failure is usually on the surface of the oak.

Regardless of how well you do your work that is the likely result you will get.

The way to avoid failure is to limit the shear stress on these joints to below 1900psi. Few people compute the shear load on laminates. They just blame the epoxy.

[bainbridgeisland]

Actually, most epoxy joints do not fail due to shear stress.

Virtually all glues, epoxy, resorcinol, polyurethane, etc. are strongest when loaded in a combination of shear and compression. Force your palms tightly together and rub them back and forth. This is an example of the kind of loads where glues perform best.

Peel or cleavage loads are the most common causes of glue joint failure. Relatively rigid glues, like epoxy, are the strongest in shear and compression but the weakest in peel and cleavage. Typical values for boatbuilding epoxies are 2,100 pounds per square inch (psi) shear strength and 2 pounds per linear inch (pli) peel or cleavage strength.

You can see that most glue joints would be very sensitive to good glue joint design. Turns out that traditional boatbuilding joints depend heavily on fasteners to resist peel or cleavage loads. We cannot simply substitute epoxy into these joints and expect good performance. Modern glued wooden boatbuilding joints are quite different from traditional joints

Therefore, chemical compatibility between glue and substrate is important, but joint design is equally important.

[thechemist]

I follow, Dave.

You can use the search thingy [upper right] to dig out threads in B/R with resorcinol in the body of the message. There was some discussion recently about proper curing termperatures.

[This message has been edited by thechemist (edited 09-30-2001).]