Epoxied to kevlar outfitting failure

Last year I used West’s 105/205 epoxy to install outfitting in a Milbrook ME. I also used West’s 403 microfibers to thicken up the epoxy.

Two of the air bag anchors failed a couple months after initial use. They did come under a load. Now after being stored all summer and into this first cold snap, I pulled the boat out and found that almost every anchor point has either developed a crack in the epoxy or has completely pulled away.

I thought I was very careful with the preparation and installation. I used acetone fairly liberally and repeatedly. I thought I was careful about temperature and cure time but maybe not. I probably kept it at 50+ degrees for a week after the repair. I did take it out in the cold paddling after maybe 2 or 3 weeks of curing. I also applied an enamal paint after maybe a month of curing.

Here are some pics


I’m looking for suggestions here.

weak mechanical bond
was the underside of the plastic anchor roughed up well? Mikes suggestion sounds like dynamite. When I used 1" plastic d-rings in less demanding application it was with 1" webbing and no glass cloth. Had to used tape covered bricks to hold the webbing down while curing. A split straw over the flat section of the d-ring prevented epoxy from sticking the d-ring.

held up great except for two sections that were in direct sunlight and degraded after ten years.

Roughed up
Thanks and yes, the plastic squares were roughed up quite a bit with a belt sander. The one pic shows how the epoxy adhered completely to the plastic. In every case the bond failed at the kevlar, not the plastic.

Timely for me, as I am about to glue
d-ring pads to my new Millbrook. The suggestions I might have made (G-flex, drilling pads, using fabric pads instead) have been ably discussed already.

An old Millbrook is likely to be rather flexible along the bottom, because back then, Kaz did not have Speretex stiffening fabric like that used on my boat. What this means is that, if a stiff gray plastic pad is glued with stiffish epoxy, contacting a relatively small area, and with rather sharp transition zones in stiffness at the border of the pads, then a couple of things can happen. One is that if the boat hits or rolls over something, the localized stress may pop one or both of the outer ends of the pad loose, epoxy notwithstanding. The other thing is that when the boat’s flotation bags, or (in the case of thigh straps) the boater’s thighs, apply upward pressure on the pad, the inner edge of the pad, next to the D-ring, may pop loose. In the latter case, we need to remember that an overheated air bag, or the paddler’s thighs, can exert so strong a force that, in an ABS boat, the inner layer of the ABS can be pulled loose. So the magnitude of these forces need to be respected.

Still, Clarion, you say that you had not put the boat to hard use when the pad failures occurred. But I still think the inflexibility of these pads, lying on a fairly flexible hull, is suspect. So, the McCrea fix, very similar to what we c-1 boaters use for thigh straps, is the best course.

I have smaller grey plastic pads, made by Dagger, and I plan to try them on the sides of the boat, epoxied over the stiffish Spheretex zones. I had already planned to drill the pads to improve adhesion. I will use traditional viny/fabric d-ring pads to hold down the ends of the 48" bags, and frankly, I have not decided what adhesive to use for those pads. But they will be flexible, so they can ride with hull fluctuations.

Again, I think we need to keep in mind the stresses we put on these pads. With float bags, for example, I drove from Atlanta to 5500’ without relieving the pressure in my air bags, and parked the car in a sunny lot while we took a short hike. When we approached the lot again, I saw a marked bulge in the Royalex hull of the MR Synergy. Surprisingly, this bulge occurred between the vinyl D-ring pad and the bow of the boat. The pad did not come loose.

I think you may have nailed the failure

– Last Updated: Nov-22-08 11:10 AM EST –

The first and only significant trip in the boat after outfitting was a 2 day camper on the Shavers Fork of the Cheat. The first day was very bony and below minimum recommended levels. There was definately repeated and significant flexing going on. For some reason the failures didn't occur right then and there. They took a while in storage and temperature changes to really show themselves.

Good thinking. It puts my mind at ease a little. I was very careful about prep and execution and thought I followed every direction. That hull flex caused it makes perfect sense to me. I can tell you there was plenty of that going on in a loaded boat.

As an aside, the fiberglass over Kevlar with no gel-coat performed in those rough and very bony conditions just as you have said it does. I was sure the boat was much worse for the wear after that first day. But nope. There was nothing but light scratching. She's a great tripping boat. Can't wait to do Shavers again this spring.

the sharp transition at the plastic edge provided a starting point for the failure at the hull then it “zippered” from there.

So something between what you used and a rubber/vinyl d-ring patch used on inflatables make sense. The g-flex epoxy with cloth webbing sounds like a good suggestion.

Lemme add to speculation on getting
epoxy to stick. So Clarion, you really did a good job on cleaning the old laminate. You sanded or scuffed it to raise some fuzz for the epoxy to grab.

Let’s think about what we have here. The existing Kevlar fibers are thoroughly interpenetrated with Kaz’s vinylester resin. So, while the surface is kind of rough, it really may be less susceptible to surface penetration by the resin than dry wood. The bond of the epoxy to the surface depends on the bond of epoxy to the exposed sides of Kevlar fibers at the surface of the matrix, the bond to exposed old vinyester resin, and the bond to those standing-up Kevlar fibers from sanding. As strong as Kevlar is, those fuzz fibers by themselves are not enough to preserve the bond, especially if there is a “zipper” failure where the Kevlar fuzz can be flanked and attacked almost one at a time.

Now, while I don’t agree with Salty that Kevlar has marked deficiency, compared to other fibers, in bonding to resins, the little data I have been able to collect suggests that Kevlar to resin bonds may be a bit less that average, as boat cloth goes, in bonding. So it is plausible that trying to get epoxy to bond to Kevlar might be just a bit more problematic than getting it to bond to glass cloth or to polyester (CAP).

Finally, with a bond not all we might have expected, and a stiff d-ring pad glued to a normally flexible laminate, we do have some potential for a zipper type failure.

Maybe I’m missing something
I can’t see any impact or failed plastic. Look at this photo:


Mad River paints the inside of their hulls. It looks like when the D-ring came out, it pulled the paint with it so the structural failure was the paint’s adherence to the boat. The Plastic D-Ring and base are doing just fine.

The D-ring was scuffed and the areas were cleaned, but nothing was mentioned about sanding the boat to accept the patches.

So the failure here is not removing the paint prior to installation.

picture isn’t the greatest
… but I did clean the areas very well and repeatedly with acetone. I scrubbed acetone into it with a copper brush and sand paper and made sure I got all the paint off as well as some areas of conctact cement from old kneeling pad locations. That’s not to say I’m positive I did everything 100% correct as far as surface prep goes, but I worked really hard at it and it sure took a long time. The color in the pic you referenced is kevlar gold.

Thanks guys
I feel much better about this now. After I clean all this old stuff out, I’m going to get some G-Flex and use nylon webbing install the metal D’s in the way Mike suggested using a fiberglass overlayment. I’ll use LeeG’s split straw suggestion too.

If anyone else has theories or suggestions, let’s hear those too. I sure appreciate the help.

Clarion after wiping, cleaning, prepping
with whatever you end up using … sand the areas for prep one more time but DO NOT wipe with acetone … this is killing you ( repair success ) patially before you even start.

Sand the surfaces, blow / wipe little bit of dust off, that it.

In addition, this is a Millbrook ME.
Millbrook does not paint the inside of their boats. Clarion painted the inside of his Millbrook after he glued the D-rings in.

I didn’t know that
I probably wiped with acetone as a final step. I can’t be sure I did, but it sounds like something I would have thought was a good idea at the time.

Thanks Pat.

Here’s another theory. Kevlar does not
wick water when protected in a resin matrix. But when one sands and prepares the laminate prior to epoxy gluing of the d-rings, one cuts into and exposes the Kevlar fibers. Now, this is no problem if the Kevlar is protected by the NEW epoxy resin, but if a crack begins to develop, for the other reasons we have discussed, then water may get into the exposed Kevlar fibers and cause them to swell. This might add to the tendency of a small crack to “zipper” under the D-ring. Maybe this was one reason why Clarion noticed a delayed effect, with the D-rings coming off after the boat was brought home and stored.

actually, this one was painted
… and I’m pretty sure it was painted from Kaz. The reason I say that is the paint is even under Kaz’s hand hand written tag. It was a grey that is a darker than the color I ended up with. The build year is '94.

You can see the original grey around the tag in this pic: http://good-times.webshots.com/photo/2631806800043436830JsFpTm

Holey pads
Mike’s idea of drilling holes reminds me of installing SS studs on pads. First use a thickened mix to adhere the pad, with the mix oozing through the holes. Then cap with epoxied fabric patches.

But the hard plastic patches are probably dificult to adhere permanently. Webbing should be stronger.


I actually followed his idea
If you look crosse-eyed at the one blurry pic you’ll see that I did drill holes in 'em.

Harold Deal’s outfitting on his Shamen uses the plastic pads but then he covers the whole top of the pad with thickened epoxy too. I don’t know if he also drilled holes. His epoxy has a brownish tint, ?.

Here’s my experience
We’ve had professionals and interested folk weigh in here with their real experience. Here’s my shot, but, without seeing the hull I just don’t know, and seeing it might not help much either.

We’ve had 5 failures of plexus to bond plastic/ carbon laminate or dymondwood to Kevlar out of roughly 4000 applications. Most of those were early, when we didn’t clean the kev with acetone, and sand and clean the various plastics with acetone. Surface prep is almost everything

I wouldn’t use epoxy. Jamestown sells $11 plexus applicators. Plexus flexes a little, which may help.

Works for us, and I’d guess works better with the hard plastic ring holders.