Tag Archives: Tom Pawlak

Gougeon 12.3 canoes

The Gougeon 12.3 Canoe

by Tom Pawlak

Epoxyworks 29

Cover Photo: A small sampling of the Gougeon 12.3 canoe family. Robert Monroe’s cold-molded canoe (foreground) came from a half-mold that eventually resulted in the a 12.3 mold (object directly behind first canoe) which has been used since 1989 to produce dozens of offspring that reflect a wide raged of tastes and technology.

The Gougeon 12.3 canoe represents several decades of experimentation by employees of Gougeon Brothers. Dozens have been built but no two are exactly alike. The evolution of the Gougeon 12.3 parallels our love of boating, passion for innovation and desire to build better boats—all of which contribute to the products we produce today.

It started 35 years ago with a personal project of Jim Gardiner, who was an employee of Gougeon Brothers at the time. He wanted to build the lightest solo canoe possible  Continue reading

Storm the Castle

By Tom Pawlak

A while back, my nephew Robbie, about 15 years old at the time, asked for help building a trebuchet (a form of catapult) for an upcoming Science Olympiad competition that his school was involved in. He had located a nice set of plans online that were based on a lattice-type structure using hardwoods. The website offered a fairly detailed plan and included project photos to help during the build. Continue reading

Quick Lawn Mower Repair

By Tom Pawlak

I hesitated to write this article because my friends accuse me of being a cheapskate. The text and photos to follow will only strengthen their argument. That being said, I can’t be the only person who would prefer to fix something rather than buy new. Besides, I can’t resist the opportunity to experiment with WEST SYSTEM® epoxy. 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.

 

D-Ring Pads and G/flex Epoxy

By Tom Pawlak

NEW POSSIBILITIES FOR HDPE BOATS

D-ring pads are often attached to flexible surfaces with urethane adhesives to gain load carrying capacity where there otherwise wouldn’t be any. They are used on waterproof fabric cargo bags, heavy tarpaulins and inflatable boats. They are also sometimes used on the decks of canoes and kayaks to hold cargo in place on long trips. D-rings are not typically used on polyethylene canoes and kayaks because the urethane glues are not recommended for use on HDPE (high density polyethylene) plastic. We decided to experiment gluing D-ring pads with G/flex 655 to HDPE plastic with that end-use in mind. Continue reading

Installing a Removable Hatch

By Tom Pawlak

Meade Gougeon installed the original hatches on his Gougmaran, but he wasn’t convinced he had selected the ideal locations. Prior to installation he thought about how difficult it would be to remove and relocate them if he used one of the flexible adhesive/ sealants made for this purpose. There had to be a better way, one that would allow hardware to be easily removed yet seal out water. Continue reading

WEST SYSTEM Launches G/Flex Epoxy

By Tom Pawlak

G/flex Epoxy is a toughened, resilient two-part epoxy engineered for a superior grip to metals, plastics, glass, masonry, fiberglass, and wet and difficult-to-bond woods. Introduced in June 2007, G/flex Epoxy is currently available in two consistencies: G/flex 650 Epoxy, a liquid epoxy, and G/flex 655 Epoxy Adhesive, a pre-thickened epoxy. Both have a 1:1 mix ratio.

G/flex Epoxy gives you 46 minute pot life and a long open or working time of 75 minutes at room temperature. It will reach an initial cure in 3–4 hours and a workable cure in 7–10 hours. Wait 24 hours before subjecting joints to high loads. Continue reading

Borate Salt Treats Decayed Wood

By Tom Pawlak

Sodium borate is used in a number of commonly used household products from laundry detergent to hand soap. It is also used to treat wood against insect and fungal attack. Sodium borate is refined from borax, a natural mineral, which is mined throughout the world. One of the largest deposits is in the Southwestern United States. (Think 20-Mule Team Borax™, Death Valley Days radio and TV shows).
Continue reading

Pot repair with epoxy

One-Shot Pot Repair

By Tom Pawlak

My wife Mary and I recently went to the local building center to purchase a large planter pot for our patio. After we had agreed on a nice large terra-cotta beauty, I noticed another large pot that had a serious crack. I asked the associate for a price on it, knowing it would be easy to repair with WEST SYSTEM® epoxy. He said I would be doing him a favor if I took it away. So we came home with two pots for the price of one. Continue reading