Inconsistent epoxy wood bonds

A revealing study done on explaining the inconsistency of epoxy-wood bonds and their improvement.

http://www.evenfallstudios.com/woodworks_library/are_epoxy-wood_bonds_durable_enough.pdf

The FPL-16 referred to is also known as "Hughes" epoxy.

It also might explain how some additives or fillers that increase epoxy resilience might improve bond durability.

Dino

 

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The requested URL /woodw...ble_enough.pdf was not found on this server.

 

Sorry for the bad link. Try the attached file.


Dino

 

Very interesting and above my understanding level.
However (you didn't think I would give up just because I don't know anything, do you), the goal of most epoxy/ wood boat building it so isolate the wood from contact with water, limiting the moisture content gain used as a primary test for this article.

Since the level of moisture gain was never stated I wonder if it has any applicability to epoxy boat building? I certainly understand a degraded bond if you don't completely cover the wood with epoxy, therefore picking up significant moisture in the wood.

What is the relevance to current wood epoxy boat building?

Of course, any pre coat that improved the adhesion of a dry wood bond would be a benefit to everyone, but another miserable step in the process.

Any idea if this article applies to that question?

Thanks for showing the article.

But my experience with boats (limited compared to some) says that in dry wood there is no issue with bond strength.

 

I started reading and got to the second page and realized they really didn't have a grasp on the chemistry, nor the typical attributes of the more common formulations.

For example they assumed because epoxies typically couldn't pass ASTM D 2559 or ASTM D 905, that it wasn't considered suitable for exterior exposure. I guess all our wooden boats, all our composite structures, including the latest America's Cup contenders, the wings and tails surfaces on most of the newest aircraft and the wind turbine blades throughout the contry are just going to fall off soon.

The first tests they site are the Olson and Blomquist (1962) studies, long before modern formulations made it a viable and practical coating, let alone an outstanding adhesive, even in exterior applications. What a worthless set of tests to site and remotely remain non-laughable. In the footnotes of test results and contributors, not a single formulator was listed and the epoxy formulations used in the tests don't exist any more. Absolute garbage and contradictory to peer studies and independent testing, not to mention the countless exterior applications that haven't fallen apart yet.

Even though Charles R. Frihart, the author of this piece, is a USDA Forest Service tech of some sort, the USDA Forest Service and the Forest Products Society disavows any conclusions therein, which is telling in itself.

 

I believe in the integrity of wood epoxy bonds and have used multiple formulations for many years with success. However my experience and others is anecdotal and insufficient for some builders see below:


http://www.forestry.gov.uk/pdf/FCRP015.pdf/$file/FCRP015.pdf

http://www.google.de/url?sa=t&rct=j...JRbc_za-YoHM2Ro_383YxWw&bvm=bv.55617003,d.Yms

In my previous post, Frihart concludes that wood swelling can exert local forces exceeding 100,000 psi resulting in bond interfacial strain exceeding the strength of epoxy. MME or MUF primer coats largely eliminate the problem. Maybe these treatments or using fillers that improve resilience allow the epoxy to distribute local loads more evenly throughout the bond line. It may be cheap insurance to improve bond durability.

Dino

 

Dry wood - wet wood.
Lets talk about what was tested and how it applies to current boat building.
An innapropriate test can generate all kind of useless data.

Do you know what was tested?
Maybe I am off track - but I doubt it.

 

The HDT of 110-120 F for epoxy is very easy to reach. That's a concern.

That Gougeon Brothers states that after one million stress cycles, or about 5 weeks in waves, 40% of epoxy bond line strength is lost is another concern.

Epoxy doesn't sound so good if those facts still hold true.

 

Very easy to get a bit depressed reading that chapter especially concerning power boats. Fastener strength is a bit more encouraging , so pass me the square drive galv screws then the epoxy will stick good

 

SamSam,

It is easy to read hysteria into the simplest of information.

40% of what?
How much was it designed for?
What was the spectrum they used?

How much do you need?

If you can't answer all of those questions then getting excited about 40% is a waste of time.

What is the equivalent degradation for Titebond 2 or 3, Rescorcianl (spelling), and anything else you propose?
What is the equivalent degradation for traditional wood construction which gets wet thru-out.

I don't doubt the fact if you got it from the Gougeons.
I doubt the usefulness of stating it as if it concludes some argument.

Did you also read about the wood epoxy boats the Gougeons have built and their longevity, or the windmill blades they made which were tested by the USG and their lifetime?

 

I can understand the concern for manufactures of engineered wood products. They invest heavily in tooling to produce millions of units and they need a predictable finished product that an engineer can use when specifying their product.

How does this affect me and my use of epoxy ? Already virtually all my work is substandard and cant be relied on to achieve the known mechanical properties of the materials used.

This is why boatbuilder overbuild with large safety factor. Our bonding surfaces are huge, our fabric overlaps are huge. Our scantlings are huge

Even with improved bonding materials this factor would be present.

 

It's important to not read too much into these types of out of context statistics. If you want, you can find all sorts of "failure" points with any material and adhesive, but they do have to be taken in relativity with a base line and honest testing. Other wise it's just Fox news reporting.

 

Now PAR - 25% of fox news views are democrats. It is the top rated cable news service and approaching network ratings.

they are the only news reporting reporting on obamacare issues, fast and furious, Clinton/Obama murder of our Ambassador. On msnbc they just pick a different republican every day to attack....

 

You don't really want to start me up on the escapades of FOX do you? According to FOX, the national dept is going to crash the economy and killing our competitive edge world wide, yet the facts are the national dept is down by over 50% of when Bush was in power and we are more competitive in the global market then before the economic crash. Then again, you could just listen to the made up stuff over at FOX. You know FOX, where Sara Palin is someone serious to be reckoned with and the national dept is killing us . . . If using the FOX model, all epoxy structures will catastrophically fail on October 17, 2015, well at least according the amine allergic expert, they'll use to describe the situation.

 

I only believe what I hear on Fox if it's in a Simpsons episode . . .