3M 5200

Problems, how to use. Also see: "EPOXY", in the left-hand column of the Home page.

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Bluesman
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3M 5200

Post by Bluesman » Sat Jul 14, 2018 2:07 pm

I just ran into a Chris Craft owner at a show who tried to impress upon me the idea of using 3M 5200 instead of epoxy for all joints and laminations. The idea being that 5200 is strong yet flexible and epoxy doesn't give. This is a new one on me, anyone care to comment?
LeClaire, IA - Birthplace of Buffalo Bill and home of the American Pickers on The History Channel

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hoodman
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Re: 3M 5200

Post by hoodman » Sat Jul 14, 2018 2:50 pm

Sheet ply and cold molded boats are a lot stiffer and don't need to flex like the old Chris Crafts. That's why you see a lot of Chris Craft restos with 5200 bottoms. You could probably build a cold mold hull with 5200 but it is orders of magnitude more expensive than epoxy. It has its place but not practical for building a "modern" hull in my opinion.
Matt

Building a Geronimo......!
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TomB
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Re: 3M 5200

Post by TomB » Sat Jul 14, 2018 3:32 pm

Across a given width boards expand and contract more than plywood. As the boards on any wooden boat move through their expansion cycles gaps in the seams open and close. 5200 provides flexibility and adhesion to maintain hull integrity while the boards move. As an alternative, boats made with boards can be "soaked", i.e. leave it in the water until the wood swells enough to close the seams. If I had an old woody, I would use 5200. Since movement is not a problem for plywood, epoxy is a better choice.

Tom

PeterG
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Re: 3M 5200

Post by PeterG » Sat Jul 14, 2018 7:28 pm

Ditto on what Matt and Tom said. I have seen 5200 and epoxy both be used improperly and the fixes are expensive. Basically, epoxy is the best material for cold molding and plywood builds. The hulls are designed with glued and screwed frame joints and plywood planking. There isn't any expected flexing in the joints. 3M5200 is the proper material for restorations of old runabouts where the designs used screwed (not glued) joints for the boards that make up the frames and planking. Those designs have a fair amount of flexing in the hull which means flexing joints as well as expansion/contraction due to changes in the moisture content of the wood. The 5200 is used to "bed" the joints to act as a sealer to keep moisture out so rot won't start. It remains flexible so the joints won't self destruct in normal use. Epoxy on an old runabout is a really bad idea because it doesn't flex. Rather, it tears loose from the wood and let's rot begin.
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Bluesman
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Re: 3M 5200

Post by Bluesman » Sat Jul 14, 2018 7:49 pm

That all makes sense to me. I figured what he was saying was off the mark for a new build cold mold. Thanks for the affirmation.
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Jimbob
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Re: 3M 5200

Post by Jimbob » Sat Jul 14, 2018 9:36 pm

What Peter said is correct. That's why restorations must have 5200 bottoms. Epoxy is the best way to go on a new boat.
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PeterG
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Re: 3M 5200

Post by PeterG » Sun Jul 15, 2018 6:56 am

And, to add confusion to the subject, I plan on using 5200 on my Malahini.
I'll be installing a traditional planked deck (not laminated ply/mahogany) and will bed the planks with 5200 to keep the joints protected from moisture intrusion.
Murphy's Law: Anything that can go wrong, will go wrong.
Griffin's Law: Murphy was an optimist.

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