Patching Kevlar?

-- Last Updated: May-19-12 9:44 AM EST --

I'm going to start work on my 89' Kev Malecite but am wondering how to go about patching this crack:

With the Courier I used a hack saw blade to widen any cracks to clean them and make them a tad wider for resin work. Kevlar from what I've read should be cut not sawn. I am going to try my hack saw but I think that will do more damage than good. If you are wondering this crack is also "puckered" outward and is in the chine so finding a way to clamp it down is next to impossible IMO. Anyone have suggestions on how go about cleaning that damn thing up? Many thanks.


patching aramid
Are the aramid cloth fibers ruptured all the way through? If so, I would patch the hull interior of the cracked area with two layers of aramid cloth using peelply to get a reasonably smooth edge. You can lightly sand the aramid interior, then clean it well before patching.

I would forget about sawing through the crack. Before patching, I would fill in the crack using some thickened epoxy. Colloidal silica can be used or you can cut some very short lengths of fiberglass fibers off some cloth and stir them into the epoxy. To try to maintain a fair hull contour I would suggest taping a sheet of stiff cardboard or similar flexible material over the hull exterior. You might use a cam strap or two around the hull to pull in the puckered area. If that doesn’t work, perhaps you can support the hull in such a way that the puckered area is in contact with the ground and then weight the interior of the adjacent hull to push in the bulge before you fill in the cracked interior (if present) and then patch the interior.

Once you have the interior patched and the epoxy is cured the hull integrity and shape should be preserved. I would sand off the gel coat around the cracked exterior and clean up the broken aramid fibers as best possible. As you probably know, aramid can’t be dry sanded (it fuzzes upt) but I have heard of people having success wet sanding it. You could also try triming the broken aramid fibers with a razor knife. I have heard of folks burning off aramid fibers with a lighter, or applying a coat of epoxy and wet sanding them off before it cures.

I would put at least one layer of fiberglass over the cracked exterior, if not two.

Great Idea!
I have a band clamp and that should do the trick. I did talk to one character about putting a layer of resin on it and then sanding it down. I think that is the way I will proceed. Just spent an hour washing years worth of grime off of it and I can see a lot of small cracks in the outter layer. Oh well, for a 24 year old boat it is what it is! Many thanks for the suggestions!



– Last Updated: May-19-12 11:29 AM EST –

I think Pblanc hit it right on on all points. The only thing I might do differently is use fiberglass for the patch in place of Kevlar. The weight difference will likely be less than an ounce for your patch, and the 'glass is cheaper, easier to work with, and more readily available. That said, if you have it kevlar works fine too.

I've had success putting epoxy over fuzzy kevlar and then cutting with a sharp knife (I use an old Mora).

As to the cracks all over the boat, it is likely they are just gel-coat cracks. You can ignore them, or sand the boat really well and then paint it if you prefer a new look.

The best tool for working with Kevlar…
…is a carbide scraper. It will shape it without the fuzzing that occurs with sand paper. Bahco and Hyde are two commonly available brands. Look for a 2" scraper with a slightly curved blade (or double-sided, curved and straight). I find the curved blade to be more useful in general than a straight blade.

Here are a couple of examples:

Smaller scrapers like this can be useful as well.

Ideally, Kevlar inside and glass outside
Kevlar does not sand well, dry or wet, but if the fuzz seems excessive, you can torch it down to nubs and then shave it off. But I would just patch over it unless the fuzz is ridiculous.

The usual rule. Largest patch first, and so on down to the smallest.

If you aren’t going to use the Malecite in whitewater, then you just want clean patches that restore hull integrity without adding much weight.