Just how strong and durable is epoxy ?

[theoldwizard1]

So I am watching a series on YouTube about a guy building a 50+' wooden sail boat. The frames (2x6 douglas fir) have 2 chines. At the chine, the butt ends are epoxied together and then a 1/2" marine plywood gusset is placed on both sides of the joint. Small nails are used just to hold things in place until the thickened epoxy dries. It appears (from what he has assembled) there is no additional structure/reinforcement.

Anyone here ever build anything similar ? Is this adequate ?

This is way out of my league, but I would probably have fitted a piece of 2x6 doug fir to the inside of that chine angle and used a 3/4" gusset to cover all of that and the added some 1" hardwood dowels through all pieces to really lock it all together. Seems like the guy is putting a lot of faith in that thickened epoxy !

 

[ondarvr]

Epoxy holds well, but it all depends on the exact type of construction as to whether it needs more reinforcement than just the epoxy.

 

[Scott Danforth]

depends on the epoxy....the substrate....and most importantly, the prep...

 

[82rude]

Epoxy is a vast c.hem industry.Epoxy adhesives are used in the aircraft,auto,boat,golf ski industries and more.Resins or adhesives are certainly capable of doing exactly what you described.Search and read up on epoxy and you will be surprised what it can and is used for.Epoxy can be formulated for almost any app .I watched a program where a high end car was and is put together structurally with epoxy adhesives ,no welds.They stated that if you tried to separate the steel or aluminum the steel would rip befrore the adhesive.Theres hundreds of formulations of epoxy so the right one is required.

 

[Redfred1]

Can relate a quick true story. In '07 I tried to lift a L/M off of stop. Back straight; only lifted with legs. A sudden "POP" a I was on the ground. Was rushed to ER; MRI showed L4 vertebrate was crushed. Went to surgery next morning;procedure took less than one hour. Woke up that evening; nurse tells me to get up and walk.I did. Walked slowly to the chapel; got down and thanked our God in tears.Surgery was inserting needles in my back;inserting a balloon; filled it with epoxy; then removing the balloon. Follow up one week later; was released. Surgeon said it was OTC stuff available anywhere.ER early Friday; walked out the door Sunday afternoon Was NEVER in any pain. Don't know about strength; but some is inside me.

 

[theoldwizard1]

I should have mentioned, he is using West System with West 406 Silica. The wood is sanded and wiped clean (not sure if they use a tack cloth).

As I said before, the 2x6 are butt glued on an angle so there really is not a lot of surface area. There is a lot more surface area on the gussets.

As for auto assembly, I don't think they use epoxy, more likely a special polyurethane. They use a continuous bead so that the area being bonded is quite large.

 

[Ned L]

If the NA knows what he is doing, and specs it that way it should be fine.
Personally, I don't think 'hardwood dowels' as you describe would add anything. 'Dowels' really don't have a place in a boat,... for a number of reasons. (Except for treenails (trunnels)).

 

[Texasmark]

If you are dealing with wood and the epoxy adhesion was executed properly, you can break the joint, but it won't be the epoxy that yields. The wood will splinter and separate (solid white oak)....BTDT testing marine adhesives when I built my first boat. You need a fastener to put the wood in compression for the joint to hold ....with the adhesive. Through bolting with scab plates on both sides, washers and glue is best.

 

[82rude]

Epoxy can and is used in aerospace,auto,sporting and appliances.3M has many types of epoxies including 2 part industrial.polyurethane.is in a class called reaction polymers which includes epoxy.Exactly which one they used on the auto I'm not positive because they would not say but both are applicable.I remember years ago I went to change the door hinges on my buddies chevy truck and was baffled at first as there was no bolts holding the hinges on to the door until we realized they were held on by adhesives.Though I don't fully understand the chemical aspect totally I'm fascinated by the uses for epoxies and similar adhesives .I believe the question was how strong and durable is epoxy?.Depending on the formulation it can be extremely strong and durable and water proof.Texasmark is right about fasteners for compression adhesion.theoldwizard1 no argument about poly but 3m also makes 2 part epoxy that comes in a tube and is applied in a bead also.

 

[Chris1956]

As was said. epoxy and other modern adhesives can work well when engineered correctly, prepped correctly and applied correctly. When Boston did their "big dig" to build the underground main highway, they used epoxy to hold large chunks of finished concrete to the ceiling of the tunnel. The concrete had rods embedded, and matching holes were drilled into the ceiling of the tunnel. An application of epoxy into the holes and the concrete ceiling panels were installed and braced until the glue dried.

That worked well for some years. Sometime later some of the concrete panels fell onto cars using the tunnel, crushing the cars and killing some people. They fault analysis showed that the panels that fell had the fast setting epoxy adhesive, when the specs called for the slow setting epoxy. Both were approved for the job for different applications.

I submit that the safety margin of the tunnel's construction was inadequate. The tunnel should have been designed to be many times stronger than it needed to be. Gluing straight rods into straight holes, with many tons of dead weight on them is a bad design, IMHO,

So, is the epoxy glued boat strong enough? Maybe, but when I think about the beating a hull can take during a storm, I would hate to have a joint fail catastrophically, which is what epoxy can do. I would feel better with epoxy and mechanical fasteners. I would expect those joints to fail slowly, if they fail at all.

JMO.

 

[fhhuber]

With proper application, even cheap epoxy will hold until the wood breaks.

I'd look for more glue area by "finger cutting" or beveling the main pieces.

But if the ply gussets are adequate the main pieces will break beside the gussets before the joint fails.

 

[gm280]

There are tons of different types of "epoxy" glues on the market. Some get extremely hard and some basically soft. So depending on the application, you have to select the type that will best offer the qualities you are looking for. When I was building R/C aircraft, I use both 6 minute and 30 minute Devcon epoxies. And they never really got hard. The stayed towards the softer side. And if you tried to sand them it would gum up the paper real quick. On the other side of the epoxy chart, I used some white epoxy for some real aircraft issues that got hard as a rock. And it would sand and file like aluminum. JB Weld get very hard and can even be machined and taped. o for a good quality joint, it takes the proper epoxy AND the proper joint connection. a butt joint with any type glue will never be as strong as a lap joint using the exact same glue. Common sense still have to be used. JMHO

 

[Texasmark]

Iterating my point guys, it doesn't make a tinker's darn how good it holds if the surfaces to be mated disintegrate.

 

[theoldwizard1]

Iterating my point guys, it doesn't make a tinker's darn how good it holds if the surfaces to be mated disintegrate.

There is that !

I think what Texasmark is saying is, that if the epoxy fails to provide perfect waterproofing, the wood will rot.

 

[theoldwizard1]

If the NA knows what he is doing, and specs it that way it should be fine.
Personally, I don't think 'hardwood dowels' as you describe would add anything. 'Dowels' really don't have a place in a boat,... for a number of reasons. (Except for treenails (trunnels)).

Well, maybe I used the wrong terminology ! I don't really know the difference between a modern hardwood dowel and a "treenail"/"trunnel"/peg !

 

[Ned L]

Well, maybe I used the wrong terminology ! I don't really know the difference between a modern hardwood dowel and a "treenail"/"trunnel"/peg !

You used the correct term for what you are talking about (dowel). ............. (Treenails (trunnels) are large dowels that are used in very specific type of boat construction (generally large and heavy scantlings))

 

[theoldwizard1]

If the NA knows what he is doing, and specs it that way it should be fine.
Personally, I don't think 'hardwood dowels' as you describe would add anything. 'Dowels' really don't have a place in a boat,... for a number of reasons. (Except for treenails (trunnels)).

Personally, I would "feel better" if there was 4 dowels though and through those gussets and frames. (The screws are just to hold thing in place until the epoxy sets.

 

[Texasmark]

There is that !

I think what Texasmark is saying is, that if the epoxy fails to provide perfect waterproofing, the wood will rot.

Nope I was building my first boat out of White Oak and Philippine Mahogany. I was using a purple 2 part marine glue. I wanted to know how well the glue would hold. I found out when the oak splintered before the glue yielded. On preserving I agree that the preservative needs to be between the water and the wood to be effective. I like Boiled Linseed oil/mineral spirits (oil to do the shielding and the mineral sprits to dilute it enough to get down in the crevices) as it soaks in and after drying then you can put on your top coats of Poly, Marine Varnish, or a good marine paint like Interlux Marine Enamel. Thompson makes a pre mix product that's popular in the building trades market but I mix my own at my ratios.