Epoxy graphite bottom versus 2 part paint?

John Robinson

John Robinson

Well-known member
I remember a post a few weeks ago where somebody had pictures and description of a slick (no pun intended) looking graphite-epoxy bottom. I have a few questions about that:

1) Was that made using the standard epoxy that is used in the filleting and fiberglassing process, with some graphite powder mixed in? I have gallons of US Composites 2:1 slow cure still to use.
2) If you apply a coat, or is it two, to the bottom, does that preclude the need for any additional bottom paint?
3) What are the benefits of this method versus the two part paint method Eric describes in his Scaup build project.

I basically use Eric's Scaup project outline as my duck boat building bible, but I realize that project is over ten years old and even Eric does some things diferently now, and this forum is a wealth of diverse expert advise, so I am open to new ideas. Thanks in advance for your help so far. Maybe I can get Dave M to help me post some more pictures.

John
 
I remember a post a few weeks ago where somebody had pictures and description of a slick (no pun intended) looking graphite-epoxy bottom. I have a few questions about that:

1) Was that made using the standard epoxy that is used in the filleting and fiberglassing process, with some graphite powder mixed in? I have gallons of US Composites 2:1 slow cure still to use.
2) If you apply a coat, or is it two, to the bottom, does that preclude the need for any additional bottom paint?
3) What are the benefits of this method versus the two part paint method Eric describes in his Scaup build project.

I basically use Eric's Scaup project outline as my duck boat building bible, but I realize that project is over ten years old and even Eric does some things diferently now, and this forum is a wealth of diverse expert advise, so I am open to new ideas. Thanks in advance for your help so far. Maybe I can get Dave M to help me post some more pictures.

John
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John,

I've used it on the last 5 or so boats I built and really like it. It is just epoxy with graphite mixed in as a filler. I also use US Composites epoxy but order the graphite from Raka. It doesn't take much graphite, maybe a couple of ounces (volume) of graphite to 20 or so ounces of epoxy. If you overload it you won't have done anything but waste some graphite, once the epoxy is saturated with graphite the excess settles out on the bottom. I'm no expert but since the bottom doesn't see any direct sunlight I don't feel like its necessary to paint after the graphite coating. Also paint kind of defeats the purpose of the graphite. I sand with down to 150 or so once I'm done. As for advantages vs 2 part paint, I don't know.

Brad

Brad
 
John,

I don't know the specifics and haven't read up on it, but I am concerned about exposing epoxy to sunlight in the graphite/epoxy mix. It is amazing how fast the UV degrades it. Sure, the graphite woudl be a pigment and act as sunblock for any epoxy not at the surface, but epoxy is still exposed to the sun at the surface.

I wouldn't think this was such a big concern, but in building my boat, I got straight epoxy on my trailer in a bunch of little places. I've always stored my boat out of the sunlight in a portable garage, but in a year every piece of epoxy on the trailer had yellowed and fallen off, even underneath out of direct light.

If I wanted slick coating, I'd use the comercially available stuff Pete used on his BB.

Tod
 
Thanks for the replys. Actually my motivation isn't a slick bottom so much as just using what I have on hand while the boat is upside down rather than deal with paint right now. I thought I could get a step ahead by just buying some graphite powder, mixing it into some of the epoxy I have on hand, paint the bottom with it, add keel and stringers and flip the boat back right side up, rather than order the paint and study that process right now.
 
I have never used a primer and I'm very happy with the results.

Use Parkers or FME and paint right on the epoxy without a primer (after sanding of course). If your epoxy is new it will take quite a while for the paint to cure because ti reacts with the epoxy, but in a week or two (especially if you get ti in the sun), you should be able to flip and get it on a trailer if you are careful. You get a great bond when done that way.

Graphite would make the epoxy hard to paint in the future as well if you ever wanted to.

T
 
If you are going to epoxy the keel and stringers??? on, I think you want to do that before paint and especially before any graphite to prevent any bonding issues.
 
Lee, I was planning on epoxing the stringers on as per Eric's Scaup build. We epoxied and screwed them through the fiberglass on my buddy's Snow Goose build. I always felt bad about puncturing the glass bottom, I like Eric's straps to hold the stringers in place while the epoxy cures better, no holes in the fiberglass. I can see how the graphite could effect the bonding of stringers to hull in a negative way. Even though I have a long way to go before launching, I guess it's time to start ordering paint to do the bottom before flipping back into the cradle for decks, coaming, floor and finishing details.

John
 
Called West boys regarding graphite and the UV issue. Basically the tech guy said the epoxy will chalk, but over time slowly, depending on the amount of exposure to sun and the direct/indirect light it catches.

On the side, he did his duck boat that way, 5 years, in the garage, no issues.

On the other side, buddy did his FISHING boat, outside stored, 6 months later, all chalk.

In the end, he read some statement from the company saying they can not say graphite will protect from UV, but only slow down the epoxy deterioration.

His next comment was to just paint it if there was a problem or worry.
 
You could always overcoat with clear UV resistant poly...but then you are just adding more work for no gain. The keel and keelsons need epoxy to epoxy for bonding. If you paint it first, the epoxy will stick to the paint...then the paint is trying to hold them on.


P.S. The good UV poly's cost more than F'n Miracle Enamel anyway.
 
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