I have a question regarding Kevlar/carbon constructed kayaks and was wondering how owners of such kayaks maintain (or repaired) the resin coating over the years (I'm specifically addressing the inside of the bottom of the hulls, here, where there is frequent wear, just in front of the seat).
So, let's say a kayak manufacturer makes a lightweight kayak out of Kevlar/carbon fabric and bonds the material with vinylester resin (i.e. a light layup). Because their main concern is keeping the weight down on the boat (rather than increase its durability and, therefore, weight), they don't use as much resin in the construction process. Over time, the resin wears on the inside of the hull (cockpit area) from regular use. How are people repairing this kind of wear? Let's say the wear is significant enough that you can see very tiny pin holes between the fabric weave, so water is infiltrating the fabric/lamination. Otherwise, there is no visible damage.
I see epoxy mentioned as a possible way to repair it (e.g. using a light coat of epoxy to seal the fabric). How long does this type of repair last? I know epoxy degrades with UV exposure--does the epoxy coating turn white and flake over time (1, 2, 3 years...). Just wondering how people are handling issues such as this and how such repairs hold up over time.
Thanks!
The resin normally does not sit above
the cloth. And because Kevlar can “fuzz”, the outside of the hull really should be S-glass only. SSKK is the optimum cloth schedule for those cloths. Carbon wears easily, and should be an inside layer.
I use Kevlar/Carbon crossweave for patching, but not otherwise. The carbon wears, the Kevlar fuzzes.
Inside the boat, a wear area can be protected with a single layer of polyester (Diolen) cloth, with either epoxy or vinylester resin.
I assume you know that vinylester resin does not “keep” in storage, while epoxy does.
I should add that builders do not use
“less” resin to build a light boat, and that epoxy painted over the surface will not turn white or flake if the application was done properly.
answers
It is pretty common for builders to not fill the weave of whatever the interior cloth is. Over time, the epoxy or vinylester resin can abrade off the raised cloth fibers and the fibers can begin to abrade.
It probably takes 6 month of continuous UV exposure before most epoxies start to degrade significantly. When they go, however, they can go quickly, turning chalky and starting to flake off.
Years ago, it was pretty common for canoe makers to paint at least the interior hull bottom of their composite canoes with aramid interiors, presumably to protect the resin and cloth from UV degradation but it seems much less common now. In truth, unless you are out in your canoe for hours a day, most days of the year, you probably don't have to worry about UV exposure to the interior of your canoe, unless you store it outside, in the sun, gunwales up.
The interior of a kayak should receive so limited UV exposure that it really should not be a problem.
I have used West Systems epoxies (and epoxies from other makers) on a whole variety of canoes and some kayaks, from varied manufacturers made using vinylester resins, and I have never had a problem with bonding if the surface was prepped.
Unless you saw a lot of visible damage to the cloth fibers on the interior of your boat, I would just give the worn area a light sanding and through cleaning finishing with denatured alcohol, acetone, or both, and then apply one or more coats of epoxy.
You could, of course, use vinylester resin but you often have to purchase it in greater quantities than you need, it has a limited shelf life so whatever you don't use is probably worthless, the Methyl Ethyl Ketone Peroxidase catalyst will make you blind if you get it in your eyes, and it works no better than epoxy.
Mine was wearing where my heels
rubbed when they were on the foot braces.
It is a Carbon/Kevlar QCC-700.
I called Steve, (at QCC) and he said it was a simple fix by just cleaning it good and then putting a coat or two of epoxy over it.
That was three years ago, and it has held up just fine ever since.
Jack L
I’ve seen studies showing that Kevlar
darkens with UV exposure, but initially the laminate actually gains strength.
I have not seen such marked chalking, and flaking, of 105/205 I have used for exterior patches.
Thanks for all the reponses
Seems like an inside coat of epoxy would be a good idea if there is wearing away of resin. Luckily, there is no fraying of the Kevlar just yet, just very, very small pin-head perforations between the fabric weave.
Does anyone know if the Kevlar/carbon layup used in Impex kayaks uses a core? I know the K-Lite layup does, but I haven’t found anything to confirm whether the Kevlar/carbon layup does.
Thanks!