Repair of foam core kevlar

-- Last Updated: Jun-19-10 6:52 PM EST --

I was given a foam core kevlar (Duraflex) canoe. There is a 7inch vertical crack at midship. This canoe had been left out in the elements and will have to have all wood parts replaced including the gunwales. I took this on as a challenge, However, don't know the best way to repair the crack. This canoe, if it can be repaired will only be used on a pond on my property.

The crack is in the foam core? Inside?
What do you mean “vertical”?

If you also have to replace the gunwales, you may need to seek a craftsman in the area.

Just remember one thing before you start, you can’t sand Kevlar, makes a fuzzy mess.

Bill H.

this could help

perhaps not but it sounds a bit similar

Just use fiberglass

– Last Updated: Jun-20-10 5:37 AM EST –

roughen the area up with sand paper, wet out a fiberglass patch with epoxy and smooth it on over the crack.
If it is on the side of the boat, make sure you have the boat on it's side when you do it, so the epoxy won't run.
Tape a piece of clear plastic, (like overhead projector film) over the patch, and the next day when you peel it off it should be nice and smooth.
If it is rough, sand it lightly and sand any edges of the fiberglass, and then give it a second coat of just plain epoxy.

As some above said don't try to use kevlar. You will go out of your mind trying to cut it !
Jack L

Cutting and sanding Kevlar.
First, Kevlar can be cut either with the highest quality big scissors you can afford, or with cheap office scissors. Hold the Kevlar deep in the throat of the Kevlar and cut with short strokes, NOT with the full length of the blade. With each stroke, pull the scissors back slightly. This introduces a grabbing and slicing component to the cutting action. This approach has always worked for me, though it is slow and requires patience.

Second, if one is going to patch Kevlar, one has to sand it. And some fuzzing actually makes the patch stick better.

Third, it’s hard to give advice about patching when one does not know the location of the damage, and the probable identity of the layup being patched. If the patch is laid across a cross-crack on the surface of foam core, then several layers of patch may be needed. A layer of glass may just crack again. Kevlar is stronger in such an application, and even polyester cloth would be preferable.

Next time I want some kevlar cut, I’ll…
send you the big piece with the dimensions I want, and you can do it for me and then send it back.

I gave up on cutting kevlar a long time ago with my first patch.

I will be doing a patch within the next month on kevlar, and believe me it will be out of fiberglass.

Jack L

Repair of foam core kevlar
I am quite able to replace all the wood on the canoe to include the gunwales. I have worked with fiberglass 50 years ago making surfboards. But the methods and materials have changed since then. Someone asked about the crack. it is midship and 6 - 7 inchs long starting at the gunwhales and going south (down) Thanks to all for your help

cutting kevlar
Kevlar is best cut with a serrated scissors. Fiskars makes a craft scissors with one serrated edge and a spring loaded handle that works quite well. A roller cutter can also work.

Dahle All-Around shears

If any scissors can cut it, these will. I’ve been using the same pair for ten years at work and I’d put them up against any other pair for tough material. Self-sharpening micro-serrations and unique blade shape are the secret. If you don’t agree, I’ll buy them from you.

Kevlar is also about 5x the price of glass, and only stronger if you consider equal weight (i.e. three layers of glass beats one of kevlar), and it doesn’t sand, so mistakes are tougher to correct/refinish.

I’ve heard kevlar can “float” in the resin, thus not sticking as well when wet out unless it is compressed as in vacuum bagging.

I’m for glass all the way.