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A couple weeks ago, I was surprised to find that my Jackson Monstar whitewater kayak had a 6 inch crack in the bottom.   I contacted their customer service and they said to fill out their warranty form, even though the boat is 5 years old and it was very unlikely that it would be covered.  After submitting the form, they said my boat wasn't covered under warranty, but they would offer me a new one at wholesale.  I was pleasantly surprised by this offer, but I didn't feel like the boat was beyond repair.  So I asked if it could be welded, but they said the boat is made of out Cross Link plastic, which cannot be welded.  They did suggest using G Flex epoxy to fix the crack though.  Here's the process I used from the instructions.


  • G/flex 655-8 Epoxy Adhesive
  • Isopropyl alcohol
  • Paper towels
  • Paint mixing stick
  • Disposable latex gloves
  • 2" cellophane packing tape (or duct tape)


  • Drill with 1/8" bit
  • Sharp knife
  • Saber or hacksaw blade
  • Chisel
  • 80-grit sand paper
  • Butane/propane torch
  • Painting breathing mask


The first step is to drill out the ends of the crack.  It is extremely important to drill out the very center of the end of the crack.  If you are off to the side, then the crack can "skip" around the hole and continue past your patch.  I used a drill bit for wood and it worked pretty well.

After the holes are drilled, the G/flex instructions say to "Open up the cracks and splits with a saver or hacksaw blade to create a slight gap in the break."  I used a hacksaw blade (18 teeth per inch).  I had to start in the center of the crack to get the saw blade through the crack.  I then cut towards the end hole, reversed and cut back to the other one.

Next the G/flex instructions say to "Bevel the edges of the crack with a sharp scraper like end of sharp chisel or with a cabinet scraper to create a 3/8" to 1/2" long bevel on both sides of the split and on both sides of the hull."  I ended up using a wood carving tool.  I found it difficult to create as wide of a bevel as recommended because of how thin the plastic was.  An angled planing tool would probably have been a better choice, but I don't have one of those at this time.

Next the G/flex instructions say to "Sand the beveled surfaces to round the edges and create more taper with 80-grit sandpaper." I cut about a 2" wide piece of the sandpaper, slipped it through the crack, and the pulled it through WITH the angle of the bevel.  Once I reached the end, I switched the angle for the other side and then pulled it through again.  I did this a couple of times all along the crack for both sides.  Next time I think I'll do this more than a couple of times, maybe 10-20.  Then I just sanded both sides normally, making sure to sand about 1" around the crack as well.

Because my kayak is made of crosslinked polyethylene, a high-density polyethylene, I needed to heat treat it.  The G/flex instructions say to "Pass the flame of a propane torch across the surface quickly.  Allow the flame to touch the surface, but keep it moving - about 12 to 16 inches per second.  No obvious changes takes place, but the flame oxidizes the surface and dramatically improves adhesion."  Another benefit of doing this is that it burns off all of the small "threads" of plastic that the sanding process creates.  I used the torch on both sides of the hull and make about 3-5 passes.  The plastic definitely heated up and deformed a little, but it came back into shape upon cooling.

The last step is to apply the epoxy.  This is when I put on my breathing mask and the gloves.  I used the mixing instructions provided and mixed more than I expected to use.  I didn't want to have to quickly mix up another batch because I had run out.  Once the mixed epoxy was ready, the G/flex instructions say to "Apply a bead of the adhesive to the beveled joint, overfilling it slightly.  Cover the adhesive with 2" wide cellophane packaging tape while forcing the excess (overfill) through to the other side of the joint.  Avoid using too much force, which leave the taped side under filled."  I used duct tape because I didn't have any packing tape on hand.  After applied the tape, I smoothed out the epoxy with my fingers, trying to make it flat and not push too much through the crack.

I flipped my kayak over, making sure no force was on the taped crack.  Next, the G/flex instruction say to "Spread out the adhesive on the opposite side to fill in the beveled seam.  Add or remove epoxy to fill the bevel flush."  I decided to add a ton on the inside since it would be below the seat anyway.  My hope is this will make the patch stronger.

After waiting overnight (7-10 hours), I removed the duct tape from the outside of the hull.  The patch looks really good to me and feels very strong.  The G/flex instructions say to "Wait 24 hours before subjecting joints to high loads."

I hope to take out my newly fixed kayak next weekend.  I'll report here on how it fares.