Repair splits, cracks and small holes in plastic canoes, kayaks and other small boats made from HDPE, LDPE, ABS, PVC or polycarbonate plastic with the contents of this kit. The Plastic Boat Repair Kit features plastic-friendly G/flex 655 Thickened Epoxy Adhesive, and is assembled with the do-it-yourselfer in mind.

Each kit contains 8.4 ounces of pre-thickened G/flex epoxy, protective gloves, mixing pallets and reusable mixing sticks. Illustrated, detailed instructions explain how to repair splits and cracks in plastic boats,  attach or repair reinforcement points on inflatable boats, and repair pinhole leaks in inflatables. All components are contained in a sturdy, resealable package.

G/flex has been available since 2007. Enthusiasm for this toughened epoxy continues to run high within our company and in the field because of the unique properties that G/flex offers. This product has proven popular with canoe and kayak liveries repairing molded plastic boats, including normal wear and tear on the bottoms near the bow and stern as well as cracks and splits that occur in the hulls.

Plastic Boat Repair with G/flex

Plastics historically have been used as mold release surfaces for epoxy, allowing it to release from the plastic when cured. While developing G/flex, we tested adhesion to a number of plastics with a variety of surface prep methods. We discovered that some plastics need only be abraded for good adhesion to take place. Other plastics required additional surface prep involving a flame treatment to form dependable bonds. We discovered that a few plastics, like polypropylene and acrylic and their molecular cousins, are difficult to glue reliably no matter how we prepared the surfaces.

Effectiveness of surface preparation methods for adhesion of G/flex 655 Epoxy to plastics
Plastic	Surface Prep	Tensile Adhesion (psi)
ABS	Sand w/ 80-grit	1,854
	Sand w/ 80-grit + Flame treat	1,813
	Alcohol wipe + Flame treat	3,288
PVC	Sand w/ 80-grit	1,780
	Sand w/ 80-grit + Flame treat	1,813
	Alcohol wipe + Flame treat	2,081
Polyethylene	Sand w/ 80-grit	400
	Sand w/ 80-grit + Flame treat	1,890
	Alcohol wipe + Flame treat	2,312
Polycarbonate	Sand w/ 80-grit	1,870

G/flex Adhesion Testing

Adhesion with G/flex to properly prepared plastics (other than polypropylene and acrylic) varies from about 1,700 to 3,300 psi, depending on the plastic and the surface prep used. We tested these bonds with the Pneumatic Tensile Test Instrument (PATTI). The table above shows average adhesion achieved by G/flex 655 Epoxy to various plastics with different surface prep. In many cases the adhesion is not enough to exceed the strength of the plastic, but it is considerably better than bonds between plastic and other epoxy formulations. The chart also shows the advantage of flame treating (especially in the case of polyethylene) and the advantage of alcohol wiping over sanding before flame treating.

Joint Design

It takes more than good adhesion to make a successful repair. We all know how well epoxy bonds to plywood, but it is common practice to use a scarf joint or butt block instead of a straight butt joint. Plastic joints should be treated much like plywood joints. The WEST SYSTEM Fiberglass Boat Repair and Maintenance Manual covers the importance of grinding the proper bevel when repairing a hole or major crack in a fiberglass skin. The shallow bevel angle reduces the stress concentration between the repair and the original surface and increases the amount of surface area for adhesion. Reducing the stress concentration minimizes the chance of a peel failure, which is a common way adhesives can fail on plastic surfaces. The same technique improves bonding strength in plastic panels and reduces the chance of a repair failing in peel.

 

Gluing Plastic with G/flex

G/flex has been available since 2007. Enthusiasm for this toughened epoxy continues to run high within our company and in the field because of the unique properties that G/flex offers.

Bevel and Round the Edges

To repair 1/8″ to 1/4″ plastic, we recommend increasing the surface area along the joint by beveling and rounding the edges to be glued. This strategy is effective for repairing cracks in plastic canoes and kayaks. To test G/flex for this type of repair, we simulated splits in the bottom of a thermal-formed plastic hull by edge gluing 1/8″ thick high-density polyethylene (HDPE) sheets.

By beveling and rounding the edges of the joint with a sharp object, sanding, and flame treating the surface with a propane torch, we effectively glued this plastic together. Figure 3 shows plastic being tested under deflection after repair.

Consider Stiffness

The thickness of a material has an exponential effect on stiffness. When repairing small plastic boats, the relatively thin hull helps reduce the stress in the repair because the entire bottom or side will often deflect a significant amount under a small load. Although the plastic hull shell has deflected significantly, the overall stress in the material is low.

A thicker, and stiffer panel can generate much higher stresses as it deflects and put more stress on the edges of the glue joint. Repairing stiffer (thicker) plastic parts requires more attention to the possible cleavage and peeling loads.

Use Fillets when Bonding Butt Joints

Fillets are used to increase the surface area of the joint and reduce the stress concentration, which in turn helps handle off-axis loads that can cause the joint to cleave apart. We recently performed a tensile test on polyethylene butt joints by pulling apart samples with and without fillets. The samples that used fillets required almost 100% more force to pull apart.

Filleting Basics

1. Shape and smooth the squeezed-out thick epoxy into a fillet by drawing a rounded filleting tool (mixing stick) along the joint, dragging excess material ahead of the tool and leaving a smooth cove-shaped fillet bordered on each side by a clean margin. Some excess filleting material will remain outside of the margin. Use the excess material to re-fill any voids. Smooth the fillet until you are satisfied with its appearance. A mixing stick will leave a fillet with about a 3/8″ radius. For larger fillets, an 808 Plastic Squeegee, cut to shape or bent to the desired radius, works well. Apply additional thickened epoxy to fill voids or make larger fillets. Apply the mixture along the joint line with the rounded mixing stick, using enough epoxy mixture to create the desired size of fillet. For longer or multiple fillets, empty caulking gun cartridges or disposable cake decorating bags can be used. Cut the plastic tip to lay a bead of thickened epoxy large enough for the desired fillet size. Heavy-duty, sealable food storage bags with one corner cut off may also be used.
2. Clean up the remaining excess material outside of the margin by using a sharpened mixing stick or a putty knife. Fiberglass cloth or tape may be applied over the fillet area before the fillet has cured (or after the fillet is cured and sanded).

Designed with Plastic Boat Repair in Mind

G/flex 655 Thickened Epoxy Adhesive bonds to plastics, and works with the above strategy for plastic boat repairs.

Word of G/flex has spread and we’ve received lots of calls from canoe and kayak liveries. They had damaged boats made of molded plastic that needed to be repaired quickly because their season was about to begin. The damage ranged from normal wear and tear on the bottoms near the bow and stern, to cracks and splits that appeared randomly on the hulls.

The G/flex Epoxy kits come with an instructional brochure that explains a variety of repair techniques including plastic canoe and kayak repairs and the technique for flame treating.