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Epoxy vs resorcinol or other adhesives for boat building

I've been a big fan of epoxy for a long time. It's been recommended to me as the best glue ever, and lately as a great/durable coating to be used like paint. It's so popular that companies are starting to market things as epoxies that might be related but, really are something else. FYI anything sold as a "one part epoxy" is not an epoxy at all. it's something else. Epoxies must be 2 part.

My father started building wooden model sailboat, and wanted to use Resorcinol. What?? Never heard of it. can't be good. must be toxic. use epoxy, Dad. Lately, I've heard differently, with some caveats.
This was mentioned on www.woodenboat.com forums:

http://www.cpadhesives.com/media/ClassicBoatAppendix.pdf

The upshot is that epoxy bond strength weakens dramatically with exposure to heat or (maybe?) saltwater or UV light. Additionally, epoxy's bond is not as fatigue resistant as wood. So using it as a structural bond is questionable. Using it in hot (120F+) environments is questionable. Using it in saltwater environments is questionable.

Since boats sit in the sun, tend to flex, and are often exposed to saltwater, how can we possibly use epoxies in long term situations.

I had to search hard to find any info on Resorcinol, but it's cheaper, supposedly lasts longer. But, as far as I can tell, it's really hard to find.

Comments?

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Lroy_RC4 years ago
Boys & Girls,
Maybe if you tried Resorcinol you might know its merits. First of all, next time you are at the lumber yard, look at the edge of waterprood or exterior plywood. Notice the black or reddish glue line . That glue is Resorcinol or a cousin. It has the mots guts / longevity for wood when exposed to moisture for a long time. Epoxy will fail when subjected to same wet or heat conditions . I guarentee..

Also Resorcinol is about the only glue that can bond teak or other waxy or resenous woods.. If you prep a waxxy surface with a toothing plane and wash with thinner you can not beat the bond of Resorcinol.

Try it you will turn your back on epoxy wor severe conditions!

Lroy_RC
2-part epoxy works fine for me on wood because 1. it bonds well with minimal clamping 2. you can get it in many forms: paste, syrupy liquid, quick-curing, slow- curing 3. it's waterproof. Resourcinol has one trait I've found impossible to beat, however - it bonds those oily exotic woods such as teak and rosewood where other adhesives fail. you can get it in a small kit labeled, "Elmer's Waterproof Glue," but it is hard to find and is nasty stuff to work with, consisting of a liquid resin and a formaldehyde powder that you don't want to inhale. another adhesive with a fantastic bond on just about any surface (and another old wood boat product) is 3M 5200 adhesive in a caulking tube. this is only good for surfaces that can be somewhat flexible after being joined.
lemonie8 years ago
I think that the Resorcinol product is something like the trademarked products "Bakelite" and "Formica". The phenolic and formaldehyde precursors of which are not nice. Then again epoxy two-parts aren't exactly pleasant either. Think about this: what is "marine" or "yacht" varnish? has it been developed for exactly this sort of application? Also, are you planning upon berthing the model sailboat outdoors for most of the year- how much sun is it actually going to get? L
danlocks (author)  lemonie8 years ago
heh. well, I wasn't exactly worried about the model boat; I think for that purpose almost anything reasonably waterproof will work. I was thinking about my aging fiberglass catamaran, and wondering if the failing repairs the previous owner made are due to materials (epoxy) or workmanship. I've had to redo a number of epoxy based repairs which were probably on the order of 7-10 yrs old. I can see weakened bonds in the form of easily flaked fairing compound on other repairs that are in low stress, mostly protected from direct sunlight areas of the hulls. The boat is dry stored, but since it has a number of slow difficult to detect leaks, it's subject to repeated wet/dry cycles. It's not delamination.... yet.
I answered this yesterday (comment dissapeared) Fibre-glass different, use more fibre-glass? was essentially it L
caitlinsdad8 years ago
http://www.chemical-supermarket.com/home.php?cat=14

Lots of hits when you search "resourcinol glue". Saw that wooden boat forum topic which says the DAP one is "summer grade" whatever that means and it is found at your local ACE hardware store. The link above may have the super industrial kind some prefer. Good luck.
danlocks (author)  caitlinsdad8 years ago
I saw the same thing. There's not much breadth of product availability. I'm curious about the functional merits of the two, mostly.
gmoon8 years ago
I have three or four 16 oz. cans of DAP "Weldwood" Resorcinol downstairs, and I doubt they will ever be used.

My bet is that urethanes have completely supplanted Resorcinol for almost all production use (plywoods, etc.) They are the common choice when epoxies are too expensive.

Resorcinol is pretty poor at gap-filling, too. Much worse than modern marine adhesives.
Wow resorcinol is old school, yep almost impossible to find and leaves a purple glue line, that's all I can tell you. As for epoxy, yes it UV degrades, that's what paint and varnish are for, the temp and salt water problem I have no info on.