epoxy and gelcoat keel strip?

I need to repair a small crack on my boat just aft of the skeg box, and I figure I’ll put on partial keel strips as part of that repair, since there’s a fair bit of wear in that area.

I’d like to do the repair with Epoxy, since that’s what I’ve got, and it’s stronger than polyester. My question is whether there’s any tricks to bonding gelcoat to epoxy. Do I just do it like I was laminating more epoxy on? Cure the epoxy under plastic to avoid amine blush, then paint on the gelcoat within 24 hours?

My keel strips
are just epoxy, fumed silica, and white pigment. No need for gelcoat - you’re only going to wear it off again anyway.

I mix the silica into the epoxy until it’s almost too thick, and then add the pigment, which thins it down just a touch. Then I apply it, and sand it smooth after it cures. Dragging the boat up a few beaches will smooth it, too. With moderate to heavy use, it lasts 3 or 4 years.

My boat has a green hull and deck with yellow trim. So I think tinting epoxy to match would be difficult or impossible, given the color of the thickening agents. And finding paint to match would be a pain too.

I’ve already got gel-coat matched to the colors of my boat. So I think that’s probably the easiest way to go.

Wrong procedure

– Last Updated: Mar-28-09 2:35 PM EST –

Gelcoat will bond to epoxy, but only if it's fully cured and scrupulously cleaned. That generally means heating the epoxy-patched area to ~100 degrees (use an electric space heater or work light for heat) and letting it cure for about a day (or more). The epoxy should feel very hard to the touch (tap it with a fingernail) when it's cured.

Clean it with soap and water, then with lacquer thinner BEFORE you do any sanding, or you'll just sand impurities into the surface. Alternately, you can scrape the surface (my preference, using a carbide scraper), clean it with lacquer thinner, then sand with 80-100 grit to give the surface some "tooth" for the gelcoat to bond to. Once that's done, you can apply finish gelcoat (a.k.a. "waxed gelcoat") and it will bond fine.

However, since this is going to be on keel where it doesn't show much, I would strongly consider going Wayne's route and using thickened and tinted epoxy. The color won't match the white gelcoat on the hull perfectly, since the epoxy is somewhat yellow, but it may be good enough, particularly if you're not trying to blend it anyway.

Thanks Bryan. This is what I was wondering - how gelcoat bonds to epoxy.

The problem is my hull is british racing green, and my trim is yellow. I’m not too picky about looks, but think a white keel strip would look horrible. What sort of dye do you use to tint epoxy? And would adding enough to make the mix golden-yellow, or dark green still allow the epoxy to cure properly?

why not tint with graphite. wouldn’t look bad with your green hull.