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 Post subject: Epoxy / Fasteners
PostPosted: October 4th, 2005, 2:23 pm 
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Joined: April 22nd, 2003, 8:26 pm
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Location: London, Ontario, Canada
Which method do you prefer?

I recently had a visit to my garage from a good friend.
When I told him I was bonding my boat with epoxy only and absolutely no fasteners, he just about flipped. "NO FASTENERS!! Are you crazy??
Your boat will fall apart in a couple of years from stress cracks alone.”

This got me wondering about the longevity of epoxy glued joints.
Should I back up the joints with screws or continue to build with epoxy alone?
Any feedback would be greatly appreciated.
Thank You.

Doug


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PostPosted: October 4th, 2005, 7:10 pm 
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I don't think SpaceShipOne was held together with too many fasteners. Stick with epoxy like Burt Rutan and other composite visionaries.

Stress cracks in boat building are almost always equated with cheap, heavy, and brittle polyester resins.


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PostPosted: October 5th, 2005, 7:05 am 
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Location: Paris, On
I think that reality is quite the opposite.

You use fasteners if you want to be able to easilly replace things like gunnels. I used epoxy only on my in and outwales. nice clean look, but when/if the day comes to change them, it will be a nightmear.

Just think about the contact surface of a screw, or 40 screws, now think about the contact surface of the entire face of the gunnels, there is just no compairison. also, a small brass screw in two drops of wood, then tare them apart, it wont be overly difficult. but do the same with wood epoxied together, and the wood will break beside the joint.

The ONLY fasteners in my boat are bolting the yoke, thwarts and seats to the gunnels, everything else is permanent (which i may well come to regret.... who knows, well see)


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 Post subject:
PostPosted: October 5th, 2005, 8:58 am 
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Joined: July 18th, 2001, 7:00 pm
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Location: Mounds View, Minnesota US
I used screws and epoxy on the inner gunwales and epoxy only on the outers on both previous projects.

I very much wish I hadn't, as I'd like to remove the gunwales and make some revisions. At this point, I suspect that the only way they are coming off is to cut them off and remachine the gunwales to reuse them.

The current project will be screwed on only.

Dan


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 Post subject: Re: Epoxy / Fasteners
PostPosted: October 15th, 2005, 11:00 pm 
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Joined: August 11th, 2005, 9:30 am
Posts: 24
Location: Barrie, Ontario
Doug wrote:
Which method do you prefer?

I recently had a visit to my garage from a good friend.
When I told him I was bonding my boat with epoxy only and absolutely no fasteners, he just about flipped. "NO FASTENERS!! Are you crazy??
Your boat will fall apart in a couple of years from stress cracks alone.”

This got me wondering about the longevity of epoxy glued joints.
Should I back up the joints with screws or continue to build with epoxy alone?
Any feedback would be greatly appreciated.
Thank You.

Doug


.


Longevity depends on the epoxy. Some are better than others, but:
-"five minute" type epoxies and those with mercaptans based hardeners do not tend to have good long term bond strength (there are exceptions but they are rare)
-epoxies do not fare well with UV exposure so keep them covered or keep them coated
-a large bonding surface will distribute load better and experience the less excessive strain, so small parts are often better held with mechanical fasteners (or both)
-bond lines that are thin and between two well-fit parts will perform better.

So, a properly designed, fully bonded joint can significantly outperform mechanical fasteners and can last as long as the laminate they are bonded to.

Aaron


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 Post subject:
PostPosted: October 16th, 2005, 10:00 pm 
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Location: Shelburne, Ontario Canada
As long as you really get epoxy you should be fine. Beware polyester resins that are sold as epoxy. You can tell the difference. Polyester resins will be labelled as water resistent, epoxy resins will be water proof.

The good stuff will fill gaps with strength, so even a poorly fitting joint will have exceptional strength, and will be stonger than the wood, its the wood that will break not your joint.

For a comparison of epoxy vs. poly -resins see the comparison here
http://www.sourisriver.com/reviews/
Souris uses only epoxy resins. Most canoe maufacturers use poly-resins. They are easier to work and finish, but are a poor secoond for strength and duarbility.

There is absolutely no reason to worry about epoxy resins. If you really are fitting all your joints to perfection you can use resorcinol, but I don't like it as much. It's purple, it's brittle when dry, and just not as good to work with.

The exception would be when attaching cross grain ribbing. When attaching ribs, they should be held in place only with fasteners. Gluing crossgrain material with any glue is a bad idea and will lead to splitting. Copper nails are really your only option.

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