Category Archives: Plastic

which epoxy is recommended? WEST SYSTEM 105 Resin and G-flex epoxies

105 or G/flex?

Take the quiz

By Don Gutzmer – GBI Technical Advisor

“Should I use the 105 System or G/flex® Epoxy for my project?” This is a great question. Here’s what a Technical Advisor thinks about when recommending one type of WEST SYSTEM® Epoxy over another. Let’s start by comparing the handling characteristics and mechanical properties of both the 105 System and G/flex. This will show you the advantages of each and when one system is better suited over another for your project. Continue reading

Big Red Gets His Smile Back

By Tom Pawlak

My neighbor Rollie is always coming up with these unbelievable deals along the highway between his home in Bay City, Michigan, and his cabin a couple hours north. The latest super deal was a big red garden tractor that was mechanically in near perfect working order—except the previous owner ran it into something and busted up the grille. He brought it over and asked if it could be fixed. Heres how we repaired “Big Red.” Continue reading

Azek® PVC Deck Boards

An option in boat construction or repair?

By Bruce Niederer

Wood has always been used in fiberglass boat construction, in stringers and oftentimes as core in high compression areas such as under cleats, stanchions and winches. Wood works great in these applications but we all know that the big problem with wood is the fact that it rots if it gets wet. Here at Gougeon Brothers, Inc. (GBI) we have spent long hours writing manuals and training people to use proper techniques using epoxy to keep wood dry and strong. Continue reading

Will It Stick?

By Mike Barnard

Many times each day we get questions about sticking to various substrates.  Most questions are on something that we have already tested, so we check our large database and advise on how best adhere to the surface.  Other times the request is unique and we are unsure if WEST SYSTEM® Epoxy will stick to it or not.  In the event we do not have any experience bonding to a material, we recommend testing adhesion.  Many times this means gluing a wood block to the surface, then pulling the Continue reading

A G/flex Modified Snow Shovel

By Tom Pawlak

This winter (2011) in Bay City, Michigan, we’ve seen a couple big snow falls and lots of small ones with 1″ to 2″ of accumulation. Not enough snow to bother breaking out the snow blower, so I usually shovel it by hand. About 10 years ago I fell in love with the plastic snow shovels that are lightweight and the snow slides off of them easily compared to the metal snow shovels that are heavy and snow clings to stubbornly.

My problem with plastic shovels is they wear out after one or two seasons at best because my driveway is made of fiber reinforced concrete. It is like a huge piece of 80-grit sandpaper waiting to devour my plastic shovels. 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

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

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.

 

Repairing a Royalex Canoe with G/flex Epoxy

By Bruce Newell and Stan Bradshaw

The wooden gunwales of Royalex canoes can rip a hull apart if left out in bitter cold temperatures. Somewhere south of freezing, the plastic body of the canoe shrinks while the dampish wooden gunwales expand. Unless the screws affixing the inwale and outwale are backed out, they pin a shrinking hull to an expanding gunwale, and something will give. That something is always the hull. Continue reading

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