Tag Archives: G/flex

So Stands the Mighty Oak

By Bruce Niederer

People have been building boats using white oak for centuries, sacrificing blood, sweat and tears to engineer wonderful and enduring vessels of all shapes and sizes.

Oak was often used because of its desirable properties and behavior. It is dense, strong, rot resistant, holds fasteners well and can be steam bent. In the days before glues and adhesives, oak planking was used because it would swell considerably which resulted in tight and sound hulls, meaning little leaking and dry interiors. Of course, time marches inexorably forward and eventually builders began using adhesives to augment or, in some cases, replace mechanical fasteners.

We’ve been debating the issue of gluing oak ever since. Continue reading

Repairing a Plastic Hatch with G/Flex

By Tom Pawlak

A local sailor stopped by our shop with an old plastic hatch that was slightly warped and badly cracked. He hadn’t been able to find a similar hatch to replace it. He wondered if we had an epoxy that could be used to repair the hatch. I said G/flex would likely work but to know for sure we needed to do a bit of adhesion testing. Continue reading

Make Your Own Soft Eye Pads

By Tom Pawlak

If you look closely at some of the photos in the Bufflehead article, you will notice small pad eyes in strategic locations inside and outside of Hugh Horton’s Bufflehead. Hugh makes these lightweight carbon or Twaron™ reinforced nylon line pad eyes for his sailing canoes.

He glues them onto the decks or inside his sailing canoes—wherever they’re needed to hold supplies in place or hold flotation inside the hull. The pad eyes are easy to make and are amazingly strong. Continue reading

Attaching Guide Lines to Fly Rods with G/flex

By Tim Veale

Fly fishing, particularly for Atlantic Salmon, has been my lifelong hobby. The fly rod itself has an ancient past but its technical prowess as an instrument to launch line and fly to a designated spot on the river was epitomized by the arrival of handcrafted split bamboo rods in the late nineteenth century. Continue reading

Plastic Engine Cover Repair

By Jeff Wright

My wife’s 2000 Audi TT has a very sleek shape, and these smooth lines are carried under the hood with molded plastic engine covers that provide a very clean looking engine. Unfortunately when I was servicing a burned out bulb, I attempted to remove the covers in the wrong sequence which caused a tab to snap off.   Continue reading

Camper Panel Repair

By Tom Pawlak

Todd Lynch, one of our valued employees, brought in a damaged plastic panel from the back end of an 11-year-old pop-up camper and asked if it was worth fixing. It came from his hunting camper which had been rear-ended. He just wanted it to be functional. The impact had made cracks at nearly every screw hole for holding the panel in place, making it doubtful it would last another trip down the highway. Continue reading

Using G/5 Five Minute Adhesive

G/5 Uses and Tips

By Tom Pawlak and J.R. Watson

Spot prime metals with G/5 in place of slower drying paint primers for indoor applications prior to applying latex paints. Latex paint can be applied to G/5 about ten minutes after the epoxy is applied and while the epoxy is still soft. G/5 provides a thin barrier and prevents rust that otherwise forms in latex paint when it dries over bare steel.

Model railroad set builders create natural looking surfaces by applying a film of G/5 adhesive and then sprinkling small objects onto the surface while it is still uncured. These Continue reading

Understanding Six10 Properties

By Jeff Wright

WEST SYSTEM® Six10 is a two-part, pre-thickened epoxy adhesive formulated with properties that make it perfect for many adhesive applications. Compared to other ready-to-dispense adhesives, its particular physical properties make it ideal for stitch and glue boat construction, fiberglass laminate repair and general bonding. This new formulation has a good balance between the elongation and toughness of G/flex® and the strength and stiffness of our 105 Resin-based epoxies. You can use it with as many materials as possible including wood, metals and composites. The long working time with fast thru-cure and unique shear thinning are additional characteristics formulated into Six10 that contribute to its ease of use. Continue reading

G/flex Saves the Race

By Grace Ombry

Robert Patenaude had ten miles left to reach the finish line in the Bermuda One-Two offshore race when a 30-ton whale hit Perseverance, his C&C 41, seriously damaging the rudder. Not content to drop out of the competition, he called on his racer friends to help him remove the 160 lb, 9′-long rudder from the boat while it was still in the water. He reasoned that if the contenders in the Puma or Vendee Globe races could make major repairs without dropping out of a race, he could too. Continue reading

Gluing Plastic with G/flex Epoxy

By Tom Pawlak and Jeff Wright

One of our goals for G/flex® was an ability to bond to a variety of plastics. This was an ambitious goal because 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 different surface preparation techniques on the adhesion of G/flex 655 Epoxy to various 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

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. Our Fiberglass Boat Repair and Maintenance Manual discusses 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 often helps minimize the chance of a peel failure, which is a common way adhesives can fail on plastic surfaces. Testing has demonstrated that the same technique improves bonding strength in plastic panels and reduces the chance of a repair failing in peel.

Beveling and rounding the edges of the joint increases the bonding surface and reduces concentrations of stress on the joint.

 

This joint style in an edge-glued, 1/8″ thick HDPE strip holds tight when deflected.

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 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. The article Repairing a Royalex™ Canoe with G/flex Epoxy used this same joint style.

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.

Making a fillet on the test sample billet of polyethylene. Fillets are used to increase the surface area of the joint.

The billet cut into individual, consistently prepared test samples.

USE FILLETS

Bonding surface area can be optimized with the use of fillets. Fillets are used to increase the surface area of the joint and reduce the stress concentration. The reduced stress concentration can help deal with off-axis loads which 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 (photos right). The samples that used fillets required almost 100% more force to pull apart.

A test sample with a filleted butt joint in the test fixture, before failure.

The same test sample with a filleted butt joint and after failure.

REACHING OUR GOAL

Our formulating efforts were successful. We had an epoxy that would bond to plastics and we had a strategy for making plastic boat repairs.

As word of G/flex spread, we 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 (below). Repairing a Royalex™ Canoe with G/flex Epoxy demonstrates the effectiveness of those repair techniques on a severely cracked canoe made of ABS plastic.

To flame treat a plastic surface, hold a propane torch so the flame just touches the surface and move it across the surface at a rate of 12 or 16 inches per second. Keep the torch moving and overlap the previous pass slightly. When done correctly, the surface will not discolor or burn in any obvious way. This technique oxidizes the surface and improves adhesion. For best adhesion, bond to the surface within 30 minutes of treatment.