Graphite filler

[Scott Dunsworth]

My centerboard has been faired, glassed and re-faired. Now I am coating it with graphite thickened epoxy. Seems like I read here that you need several coats then sand it smooth. Wet sanding and polishing to a supper slick finish. I think the thread was started by Oyster. Is there any thing I may be forgetting? I don't have time for to many more mistakes.

Scott

[Guest Oyster]

Little catchup here. Just blend your epoxy with the graphite mix, making sure that your surfacce is smoothe and fair and forget about wet sanding and waxing the board. I don't know how you plan on coating both sides at one time to keep from any runs, but rarely have I had to buff out any surface with this material. Keep in mind, if you wait too long, the blend is hard as anything you have ever experienced when you attempt to sand the finish anyway. I would do one side flat, letting it reach its green statis, and then flip it, scraping any runoffs with a sharp scraper and recoat, laying it on a flat sheet of viscreen. You will only need to clean up any further runs at this time. I also will hang my parts with a threaded bolt through the pivot point, and do thin coats, which will take a longer time and will generate some additional runs in the actuall flat surface sometimes.

[Scott Dunsworth]

I am coating it flat on the saw horses. I'll do the other side tomorrow.

[Howard]

Since things seem a bit slow lately, I'll throw this out as a tag along question.

I know West offers a graphite filler for their epoxy for the exact reasons Scott is using this for, but I can't see how this is supposed to work. You can't leave the epoxy uncoated or UV light will break it down, so the friction isn't on the graphite filled epoxy, but rather on the coating, presumably paint, that goes on over it.

Wouldn't any thickening agent work the same so long as you get if faired smooth?

[rlchenry]

I don't know for sure, but I think the density of the graphite mix is supposed to protect the epoxy from UV (except for the very surface layer, I guess)

[Gordy Hill]

I'd not be too concerned about UV affecting the centerboard as long as you keep the boat mostly right side up. The sun's rays might get in the cabin, but I think the centreboard trunk will block most of them.

[Ken_Potts]

When used on a centerboard there isn't much UV exposure to worry about because it's protected by the trunk when up and the water when down. There shouldn't be paint or varnish over the graphite/epoxy.

As the surface of the graphite/epoxy mix wears a bit due to the contact between the board and the trunk more graphite in the mix is exposed to "lubricate" the surface. The epoxy part of the surface wears a bit but the graphote wears more slowly protecting the underlying epoxy.

At least that's how I understand it.

[Garry]

Epoxy with graphite filler CAN be left exposed to the sun. In 1985 I finished a 28 foot sloop hull and deck. I built a companionway hatch and a forward hatch with 3/16" teak slats bonded to a plywood base in a teak frame. The 1/4" wide seams between the slats were filled with graphite-filled epoxy. The teak was kept oiled for a while and then left natural to weather.

The teak slowly weathered away leaving the seams slightly standing proud. The hatches were received far greater exposure than a rudder or centerboard would see. The graphite filler seemed impervious to the sun.

The exposed finish was slightly textured and had some pinholes from small bubbles trapped in the mixture. The surface would not have been good for an underwater fin but I did not attempt to polish it or fill the pinholes. I'm sure that a rudder and centerboard could be polished and filled for a smooth surface.

[Howard]

Hmmmmm. Use of graphite bottoms is new to me. A quick google search turned this testimonial up:

http://tomangelakis.tripod.com/graphite_bottom.htm

This suggests the benefits are slick and hard. If the sun doesn't hurt it, why not?

This might be something to consider for the bottom of a plywood dinghy. At least for the keel section. Beaching them on the rocks and concrete landings takes it's toll. I put a double overlap of Xynole polyester under the underwater bow section forward of the keel, but could have filled and faired it with the graphite mix as well.

[Brent]

I just pulled the graphite coated center board out of my boat for an inspection. After three years of hard use the board is as slick as the day it went into the boat. There are a couple of dings in the board which will get addressed. The poly rope epoxied into the leading edge of the board did exactly as intended, taking the abuse of hitting an occasional rock or mud bank, while leaving the rest of the boards unscathed.