I need a strong resilient adhesive for making large structural bonds that will be necessary during the build of a 10 meter sportfishing boat, the adhesive should give plenty of open time to be able to apply it carefully, so I though epoxy based products should work, but much to my surprise the price of toughened epoxy adhesives is very high, (30 kg of Spabond 345 made by Gurit, priced at 673 euros), and methacrylate adhesives have shorter working times, need a machine to properly dispense and are no cheap either, does anyone know about some kind of plasticiser aditive for epoxy resins or a similar solution that is reasonably priced ???
3M makes a polyurethane adhesive/sealant product called 5200 that’s specifically for marine applications. It’s not as strong as epoxy systems, but from what I understand it’s very commonly used for large area bonds (eg hull to deck). They have a fast cure version (24h instead of 7 days) as well. It’s very cheap compared to epoxy systems and is single component moisture curing so it’s super easy to apply.
http://www.3m.com/product/information/Marine-Fast-Cure-5200-Adhesive-Sealant.html
Thank you Craj1013, I did not know that those adhesives where used for structural bonding, but it certainly is true that polyurethanes are very strong adhesives, also being so slow to harden is a definitely an advantage for bonding large pieces, still, I never heared about it being used for truly structural bonds like reinforcement grid to hull, or deck to hull, but the fact that I never heard of it does not mean is not suitable for the task, still I would be doubtful untill more people chime in and comfirm its suitability, because as far as I know, only methacrylate glues and toughened epoxy adhesives are used …
If 3M 5200 is as good as some sikaflex polyurethane/isocianate products IMHO it would be good for the job becuase if large contact surfaces are present it definitely is a terrific adhesive and flexible and resilient as well.
I would like hear what other forum colleagues have to say …
I mix up epoxy resin with cabosil and microfibres to a paste consistency for structural bonding. I have no idea what the acheived lap shear strength is because i havnt done any scientific or professional coupon testing with it. Its also not very flexible so im not sure if it would be ok in areas of large movement. Then again, the methacylate adhesives dont “feel” very flexible either…
The cost is the driving force behind many choices. I mix all my own fairing compounds, and adhesive mixtures etc for this reason - its a down right ripoff buying adhesives, and other epoxy base products in a premade mixture! You dont get the “rated strength” printed on the bottle with a pre made adhesive tho, i figure this is the main reason for the high price - they have to guarantee the numbers and some certification bureaucrats may demand its use depending on the laws in your area.
You may have to do some of your own testing via coupons, and compare the results side by side, to that of a store bought adhesive, and prove to yourself what you can achieve by mixing your own epoxy adhesive. You may surprise yourself, good or bad 
Hi Groper, I had initially thought of doing it like you say, trust in the well known adhesive capabilities of epoxy and adjust tyxotrophy to “my taste” but have recently known that infused parts are (supposedly) hard to make secondary bonds with, and that normal epoxy was not flexible enough and produced a too rigid bondline that tends to fail.
I thought also that epoxy based adhesives where just normal epoxys with some aerosil/microballoons, but it seems that it is not so, it seeems that adhesives are made with rubberised compounds and that the whole thing involves some advanced chemistry knowledge and technology, not just epoxy plus some aditives, very likely, like many things this days a true robbery.
But there may be some truth in the need to use methacrylates because Herman, recently told about some trouble in teh bondlines of 49ers made in england that dissapeared as soon as they switched to methacrylates …
I am into building what I believe is a beatiful fast sportfishing boat and am afraid of risking its structural integrity due to choosing the wrong adhesive … maybe is just the fear to the unknown …
if you wish take a look to waht we are doing here:
http://www.thehulltruth.com/boating-outdoor-photos/372020-raptor-project.html
Jigger, that is an awesome project… Should be a damn sweet boat. ANd I envy your shop! 
I’ve used a few henkel adhesives. They’re freaking awesome I must say; albeit expensive. I guess you get what you pay for ultimately.
But there are a variety of adhesives depending on application. SOme are super rigid, as pointed out, that will in fact cause a weak point if flexibility is needed. Others are more flexible, for use in things like boats, cars, planes.
Even as groper points out, an epoxy resin can be used to good effect. I’ve also done secondary infusions to bond things using VE resin.
thank you, sammymatik, in regards to Henkel, as far as I know, only sell their products in small containers, I would need to buy at least in 20 kg Pails, I guesstimate, that I will need around 50 kg, so the product should come in pails or similar sized, so far Spabond 345 albeit expensive is winning, but I have been told by Herman, that methacrylates are better, but the very long working times of Spabond makes it also a very tempting candidate, after all my parts have been designed since the beggining with large glueing surfaces … still would like to hear what other forum colleagues have to say.
Not so long ago, polyester parts in botas where glued with shop made polyester puttys, and as far as I know it worked, but nowadays, everything seems to be more complicated, maybe just successful epoxy and methacrylates vendors campaigns … who knows …
A methacrylate, such as Plexus, is fast becoming the boat builder’s standard for hull-deck joints and other structural bonding. Not cheap, not a long pot life, not very pleasant to work with, but outstanding bond strength.
About that polyester putty to bond polyester parts: it ain’t great. Strictly a mechanical bond and typically way too brittle for good bonds. Not used by commercial boat builders at all these days.
Hello Jose, it’s Roger (OReely). I didn’t know you were posting here as well as THT.
Although I’m sure some of these posts are well intentioned, I don’t think they are exactly accurate.
5200, although an excellent adhesive, is not right for what you are trying to do in my opinion. Among the issues you’d have would be material run out from the joining surfaces, cure time, skin over, etc. Regular 5200 does take a long time to fully cure which would require a long fixturing time until cured. Fast Cure 5200 starts to cure fairly rapidly so you may not get enough time to assemble the parts before a dry skin develops, compromising adhesion. Neither is very thixotropic so you can’t really pile it up to ensure good contact with both surfaces during assembly. And if all that isn’t enough, when the stuff squeezes out of the joint, it gets on everything (and I mean everything). It is almost magical in it’s ability to get smeared around.
Contrary to JumpingJax post, there are still plenty of boats built with polyester putty adhesives. Arjay Technologies is just one company that is heavily involved in the putty business. They have PE and VE putties. I’ve used many of their products and can attest to the quality and strength of the polyester adhesive. Here is a link to them: http://www.arjaytech.com/
As for why polyesters may be falling out of favor for boat builders in some instances, I think it has more to due with the nature of boating than anything else. Think about what boats are these days in comparision to yesteryear. When I was a kid (40 or so years ago), your average recreational boat was probably under 20 feet and maybe went 30 knots with a single 90 HP engine. Today we build 40 foot boats that can exceed 60 knots and have 1200 HP bolted to the transom. Obviously, the dynamics of these two examples are vastly different, hence the need for more advanced materials.
In my own boat building, I try to use what works the best. As an example, my 34’ center console uses a mix of polyester bonding putty and MMA. The deck/inner liner is bonded with PE to the stringer grid and hull sides in a vacuum process. The motorwell section of the ring deck (aka gunwale cap) is bonded with MMA. I originally bonded everything with PE but when the heavier, higher horsepower engines became available I found I needed to switch to MMA to keep stress cracks from developing in the motorwell radii. I found the poly adhesive was failing owing to the additional stress placed on the transom by the big engines. When I first designed the boat, twin 225 HP outboards made me the bully of the bay. Now 275, 300, 350 HP in twin, triple, and even quads are what it takes to be the top dog. Keeping the boat from falling apart has always been my number one goal. If that requires a more expensive material, so be it. However, I’m not one to waste money on the latest fad so I pick and choose the materials best suited to the job.
As for machinery requirements for MMA, I’ve never had any pumping equipment, just hand mixing. If I were a high volume operation, I would certainly consider a pump system.
Scott bader produces some easy MMA based glues(crestabond) with no need for expensive equipment. It holds where epoxy’s crack.
Loctite, plexus and araldite have similar glues, but I found crestabond the easiest.