The Advantages of Resorcinol--Aerodux 185 Adhesive

[John Stone]

I am modifying the winch riser blocks for our stays'l sheet winches. Previously they were 4" tall and varnished with a 2" bare pad that sat on top and then the winch was on top of that. It worked well. The height was right but I wanted to match how I modified our primary sheet winch riser blocks a few years ago--with a bronze plate on top of the riser block and under the winch.

My wood supplier did not have in 8/4 (2" thick) teak shorts. So I bought some 5/4 and milled them to 1&1/16" thick. I drilled for alignment pins so they would slip around when I glued them up.

Next, I mixed Aerodux 185 which is an advanced resorcinol adhesive. A little thicker than standard resorcinol and can be used down to 50°F. You can always tell when resorcinol is used because it leaves a distinctive purple glue line. I spread it on thin and clamped it hard. No sanding. Just machined and wiped down with acetone, glue and clamp.

I have written about resorcinol before. Resorcinol is an adhesive far superior to epoxy in certain circumstances. It is not used much any more because epoxy is less expensive, does not require precise joinery, leaves a minimal glue line, and has a long shelf life. But epoxy, as an adhesive, is not waterproof. It also loses its strength substantially as it get warmed up, say from tropical sun. I have used plenty of epoxy and I like it for a lot of things. But I have avoided it on exterior wood and especially if it's wood left bare. Epoxy as an adhesive is prone to failure when subjected to saltwater and heat.

But resorcinol is boil proof, heat proof, steam proof, and waterproof. It is approved for overhead structures. It is the same glue used to make BS 1088 plywood which is built to standards established by Loyds of London. So, it's good glue. But it's a tool like any other. No one tool does everything. Another arrow for your quiver.

A quart kit from CP adhesives is about $65. The shelf life is a couple years.

I mention all this to simply share what I learned during the long rebuild of the Far Reach.

[John Stone]

The end state is to replicate the layout of the primary winch pad with the stays'l winch pad. Replace the bare teak pad you under see the winch with a varnished block and add a bronze plate on top.

[Steve Laume]

I do agree that there are many ways to do things. There are also a few reasons why Resorcinol is not used, much, anymore. What I do question is; "But epoxy, as an adhesive, is not waterproof. It also loses its strength substantially as it get warmed up, say from tropical sun". If any of this was actually an issue, there would be millions of epoxy laminated and cold molded boats disintegrating all over the world. The same would hold true for race cars and aircraft.

It is fine if you want to use Resorcinol but epoxy is perfectly fine, for exterior, marine applications and would be a better choice in most cases.

Resorcinol was the glue of choice back in the sixties and is still used in situations where conditions can be carefully controlled; like the plywood manufacturing that you mentioned. It is not the best choice for most of us and the idea that it will degrade under marine use is certainly not proven in practical use. I Resorcinol glue joint is far more likely to fail, due to a starved or poorly fitting joint. Epoxy is more forgiving and easier to work with. Strength and water resistance is not an issue.

[John Stone]

I do agree that there are many ways to do things. There are also a few reasons why Resorcinol is not used, much, anymore. What I do question is; "But epoxy, as an adhesive, is not waterproof. It also loses its strength substantially as it get warmed up, say from tropical sun". If any of this was actually an issue, there would be millions of epoxy laminated and cold molded boats disintegrating all over the world. The same would hold true for race cars and aircraft.

It is fine if you want to use Resorcinol but epoxy is perfectly fine, for exterior, marine applications and would be a better choice in most cases.

Resorcinol was the glue of choice back in the sixties and is still used in situations where conditions can be carefully controlled; like the plywood manufacturing that you mentioned. It is not the best choice for most of us and the idea that it will degrade under marine use is certainly not proven in practical use. I Resorcinol glue joint is far more likely to fail, due to a starved or poorly fitting joint. Epoxy is more forgiving and easier to work with. Strength and water resistance is not an issue.

It's a very interesting topic. I'm not a chemist conversant in all the properties of adhesives and how they perform under controlled testing. I think there is a difference though in laminating epoxy layers together and using epoxy as an adhesive for wood bonding.

I have seen these failures on my own boat. All epoxy laminated winch pads original to my boat failed. I rebuilt the dorade boxes with epoxy and they failed. I think due to UV and tropical heat. IDK. I rebuilt the winch pads and dorades with Resorcinal. The dorade were left bare. The glue joints are still perfect. That's not to say all epoxy wood joints fail. Certainly not. Epoxy is vulnerable to UV damage. No doubt about that. It has to be protected. I have seen other epoxy glue joints fail on other boats. So it's not the super adhesive that people make it out to be. It's a tool, but it has limitations.

People are going to do what they want to do. I used epoxy for my new steam bent laminated tiller. I did it because I didn't have the tight fitting joints I had in my original tiller. And I could not source weldwood glue. The tiller is varnished. It will be interesting to see how it holds up. But I bet I have seen a hundred delaminated tillers built with epoxy over the years. Epoxy is used in all kinds of construction--especially composites. My sense is they use it differently than boat builders and amateur sailors like us. They are not using it to laminate teak. They are allowing for its loss in strength during cyclic loading....I don't think most of us do that.

Poor joinery is poor joinery. Tight joints require skill. I have gotten better at it over time and mostly I am pleased. But, it's not even an issue with epoxy...so people use it. In fact epoxy works better with loose joints and less clamping pressure. But it's not going to last as long as tight joinery built with Resorcinal.

All that said, I have included some excerpts below from test results and analysis provided by Gougeon Bros (West Systems--my epoxy of choice), the US Forest Service, 3M Company, etc. The test results indicate Resorcinal based glues are a better adhesive for wood than epoxy. Better meaning stronger and longer lasting, not better meaning more convenient or easier to use. Take a look at the shear strength test when the laminations were subject to salt spray. I'd like to read that whole report so I understand the context.

Many of us do our own work. We all get to chose. I try my best to decide from a position of knowledge and experience tempered by my always developing skill sets, the time I have available for the project, how the product will be used and under what circumstances, and what my expectations are for its performance.

Anyway, it's an interesting topic.

[Steve Laume]

I question whether epoxy formulas have changed in the 25 to 40 years since these reports were made. The fact of the matter is that epoxy is more than strong enough for most applications and is certainly easier to use correctly. For something like your winch stands, that will only see compression loads it would certainly have been strong enough. I built a pair of them that are very similar to yours that have been in service for at least ten years and they are doing just fine.

I don't question that Resorcinol is good glue, but your original post made it sound like it was the best or only glue suitable for exterior, marine use. Or at least that epoxy is not suitable. This is not really the case as there are millions of boats out there, that are successfully using epoxy. In most case it is and will remain, far stronger than it needs to be. Ease of use, affordability and versatility
would tip the scales in favor of epoxy, for most uses.

[John Stone]

And I was worried the forum was dead! Ha!

Without question the vast majority of boat builders, boatyard management, and probably boat owners agree with you. Adequate to the task. Strong enough. Maybe, possibly, probably. Certainly. Depends on the task and conditions though. And, ultimately whether or not it works. "Millions of boats using it successfully." That's a big number. Clearly it is used. Often successfully. But there are lots of failures out there. No doubt about that.

There are all kind of boats having having exterior wood repaired. All the time. I see it here. My boat is on the hard in a working boatyard. It's a lot hotter here in the summer than it is New England. West epoxy was first used on the Great Lakes to build racing scows and iceboats. No saltwater or high heat there. Maybe that has something to do with it. I think how well and how carefully it is used is important too. I am sure there are plenty of work done failing to incorporate "best practices" when using epoxy. Stands to reason. Same for anything. Certainly it's critical to use Resorcinol in a precise manner. But epoxy seems to be viewed as some kind of miracle adhesive and clearly it is not. The studies indicate it has real world limitations important to sailors. Like any tool it does some things better than others and has to be used in a way that does not expose its weaknesses, e.g. UV protection over glue joints and light colored paint to reduce heat. That was my purpose in posting what I have learned and continue to learn.

I have no way of knowing whether it's been reformulated. I would not be surprised it hasn't though. Industry is alway excited to claim a product is new and improved. I have not seen any such claims and I have used it a long time. Gugeon Brothers is a pretty good company I think. If they can make it better I suspect they would.

Resorcinol is a better glue than epoxy when used properly. It's stronger under a wider range of environmental conditions. It's stronger when used on exterior wood exposed to the elements. But it requires more skill, more time, and the environmental conditions for application are more stringent than for epoxy, although Aerodux 185 can be used down to 50°F when traditional resorcinol can only be applied down to 60 or 70°F. I built my bare teak cap rails with resorcinol Aerodux 185 glued 12.1 scarf. 8 years later and 11,000 miles all in the south or the tropics and they are in perfect shape. No UV protection. My African mahogany bulwarks all have multiple scarfs glued with resorcinol. They are in sheer. Perfect condition after baking in the southern sun and being put under significant load as I run my boom vang to the bulwarks. I hope they stay that way. I would not trust epoxy to do that.

The reality is "time is money." As you said epoxy is easier to use. It's faster. Boatyards already charge too much and they know owners get agitated about it. Epoxy speeds things along. No boatyard wants to throw out expensive wood and time consuming labor because the joinery was not tight. Epoxy moves things along. And if a piece of exterior wood joinery fails 5-10 years later who is going to hold a boatyard accountable.... Its just another boat to be repaired.

We see the same thinking in home construction and repair. Short cuts. Do it faster. Move it along. Build the next house. Houses really built right...cabinetry really built right...takes time and it's expensive. People want good work but they don't want to pay for it. Neither do I. That's why I find myself doing more and more work myself. I'm sick of shoddy work. Boat, car, house. I'm tired of paying for work when the measure of success is speed.

Resorcinol has a shelf life and epoxy does not. There is no Resorcinol made in the US anymore. None. Epoxy is formulated in the US and it's everywhere and easily available. No sane business is going to abandon what's readily available for something hard to find.

I don't know many boat builders who built their own boats and then take them voyaging for decades. That seems like the real test to me. That's what I am talking about. Making repairs and mods that last.

Most people, including those on CD forum, have probably never heard of Resorcinal and even less have heard of Aerodux 185. I don't think many people will stop using epoxy. It's laughable to think so. And epoxy does many things well. Like I said, I have it. I use it too. It's pretty much an all epoxy world we live in these days. But I shared the info on resorcinol backed up by studies conducted by the companies that make the product. I think it's interesting and good for us to know so we make decisions from a position of knowledge. And those of us who work on our own boats have the liberty to use other products, if we know about them. That's why I posted it...with the pictures, so it's not just talk. Sharing knowledge. And oh, by the way, it's not hard. If we take a little more time with our joinery. If we challenge ourselves just a little more. If we spend a little more for a quart of Aerodux 185 we might find some goodness there. We can probably do better than the so called pros driven by profit more than performance. And now I'm not talking about just adhesives....

Anyway, it's not my place to tell other people how to build or repair or mod their boats. I have never done that. We all get to chose. That's what I love about being an American. Your boat, your money, your way.

[Steve Laume]

Epoxy; the cheap solution for sloppy craftsmen.

How does all of this information play out for composite boats? The Volvo IMOCAs immediately come to mind. There could not be a more severe test of materials than racing around the world in a foiling boat.

I would imagine there is still a good deal of Resorcinol used in traditional, wooden boat building. Because tradition.

I know a number of people, who are fine craftsmen, that build cedar strip kayaks. Epoxy if always the adhesive of choice. They are covered with a clear coat but are often used on very hot days.

It just doesn't seem like epoxy is an issue, when dealing with heat and salt water.

[John Stone]

Epoxy; the cheap solution for sloppy craftsmen.

How does all of this information play out for composite boats? The Volvo IMOCAs immediately come to mind. There could not be a more severe test of materials than racing around the world in a foiling boat.

I would imagine there is still a good deal of Resorcinol used in traditional, wooden boat building. Because tradition.

I know a number of people, who are fine craftsmen, that build cedar strip kayaks. Epoxy if always the adhesive of choice. They are covered with a clear coat but are often used on very hot days.

It just doesn't seem like epoxy is an issue, when dealing with heat and salt water.

Steve, you sound as if you have a burr under your saddle or perhaps you're just being curmudgeonly. You seem determined to take this down a path not warranted by the discussion. "Epoxy = the cheap solution for sloppy craftsmanship". Your words not mine--it sounds like you are determined to be offended when none was intended.

Anyway, My post was, and is, about the advantages of using a little known glue for bonding wood together on the exterior of sailboats especially when exposed to heat and saltwater as supported by scientific data along with my own anecdotal observations. I also said I use plenty of epoxy. I have a FRP boat and love it. IMOCA boats don't have any bonded exposed wood on the deck, though they have ripped themselves apart on occasion in a quest for ever lighter scantlings and the ruthless pounding they are subject too. I'm not sure how you made the leap from bonding two pieces of wood together on deck of a cruising sailboats to high tech composite construction used in race boats....

I stand by my comment resorcinal is a better choice for bonding wood, under stress, exposed to the elements in a sailboat especially in hot environments. I chose all my words carefully to illustrate my position. I took the time and attempted to share with the forum members enough info so they might be encouraged to give resorcinol a try if they were so inclined. Clearly you are not--I got that loud and clear.

Your boat, your money, your way.

[John Stone]

Here is some good news for anyone who would like to get some Aerodux 185 and try it out. CP Adhesives, which I believe is the only US distributor, is now selling it on Amazon. It's a few bucks less expensive that way too. And best of all, though the picture is for a gallon size you can get it in a quart size package. Its shelf life is about 18 months though I have used it to three years. They also sell a pint size package.

Aerodux 185 is a little thicker than traditional resorcinol and you can add thickeners so it will gap fill a small amount. If you want to know more about it you can go to the CP Adhesive website and download the instructions there. Also, Jeff, the tech rep, is really helpful answering questions.

One thing to be aware of is aerodux, like all resorcinol glues, leaves a distinctive purple glue line. Something you may not want on a light colored wood like an ash tiller. But with teak, varnished or not, I can't see it.

[Ben Miller]

All that said, I have included some excerpts below from test results and analysis provided by Gougeon Bros (West Systems--my epoxy of choice), the US Forest Service, 3M Company, etc. The test results indicate Resorcinal based glues are a better adhesive for wood than epoxy. Better meaning stronger and longer lasting, not better meaning more convenient or easier to use. Take a look at the shear strength test when the laminations were subject to salt spray. I'd like to read that whole report so I understand the context.

This appears to be the current (2005) version of the West System paper on fatigue testing: https://www.westsystem.com/wp-content/u ... atigue.pdf

Can wood/epoxy boats last for 50 years? Unfortunately, we can’t yet say for sure. Experience in the field over the next 30 years or so will give us sound answers to this question. The oldest all-bonded wood/epoxy structure is the Gougeon Brothers designed and built 35' (10.6m) trimaran Adagio that in 2005 is beginning her 35th sailing season. Adagio is lightly built (2200 lb or 998 kg total) and has been raced extensively. Adagio is expexted to remain competitive for many years to come. Ben: I checked, and yes, Adagio appears to still be sailing in 2023, 53 years after her launch.
...
Present test results suggest we can safely predict a life span of 30 years for wind turbine blades built with WEST SYSTEM epoxy. Turbine blades undergo on average more demanding service than do boats, which provides for some optimism that boats built to operate at similar stress levels should last equally long in active service and probably longer in actual years of existence.

I haven't read the paper through, although I skimmed some sections. I also can't argue with your case for resorcinol, but if saying that it's a "better adhesive for wood than epoxy" means that it's "very, very, very, very unlikely" to fail in use in this application, versus "very, very, very unlikely" for epoxy, then the difference may not be enough to matter for almost anyone.

[John Stone]

All that said, I have included some excerpts below from test results and analysis provided by Gougeon Bros (West Systems--my epoxy of choice), the US Forest Service, 3M Company, etc. The test results indicate Resorcinal based glues are a better adhesive for wood than epoxy. Better meaning stronger and longer lasting, not better meaning more convenient or easier to use. Take a look at the shear strength test when the laminations were subject to salt spray. I'd like to read that whole report so I understand the context.

This appears to be the current (2005) version of the West System paper on fatigue testing: https://www.westsystem.com/wp-content/u ... atigue.pdf

Can wood/epoxy boats last for 50 years? Unfortunately, we can’t yet say for sure. Experience in the field over the next 30 years or so will give us sound answers to this question. The oldest all-bonded wood/epoxy structure is the Gougeon Brothers designed and built 35' (10.6m) trimaran Adagio that in 2005 is beginning her 35th sailing season. Adagio is lightly built (2200 lb or 998 kg total) and has been raced extensively. Adagio is expexted to remain competitive for many years to come. Ben: I checked, and yes, Adagio appears to still be sailing in 2023, 53 years after her launch.
...
Present test results suggest we can safely predict a life span of 30 years for wind turbine blades built with WEST SYSTEM epoxy. Turbine blades undergo on average more demanding service than do boats, which provides for some optimism that boats built to operate at similar stress levels should last equally long in active service and probably longer in actual years of existence.

I haven't read the paper through, although I skimmed some sections. I also can't argue with your case for resorcinol, but if saying that it's a "better adhesive for wood than epoxy" means that it's "very, very, very, very unlikely" to fail in use in this application, versus "very, very, very unlikely" for epoxy, then the difference may not be enough to matter for almost anyone.

Better to me means it is less likely than epoxy to fail under the conditions I outlined. Make your own choice. If you are satisfied then you chose wisely. If not, then perhaps you chose poorly.

Mostly people have moved to epoxy because it's easier to use (which is a good reason as are many of the other advantageous I described) though the evidence suggests epoxy is more harmful to humans over the long run. I'm sure there are people who claimed to have bathed in it without ill affect. The safety aspect has never been my primary driver. But, I have heard it argued.