While WEST SYSTEM® epoxy has a long shelf life, age will eventually affect its handling characteristics and cured strength. When stored for very long periods, hardeners may turn darker (reddish to purple), become thicker and give off more odor. 105 Resin may lose some clarity and also become slightly thicker. Use extra care when mixing age-thickened products (stir extra thoroughly), and don’t use old epoxy if color or clarity is crucial to your project. Continue reading
BY MIKE BARNARD
In this article I’ll describe our standards for testing epoxy and how we test epoxy to determine its handling characteristics and cured physical properties.
These are the standards we follow no matter which epoxy we are characterizing.
Two-week room temperature cure
After proper metering and thorough mixing epoxy will continue to cure after it has solidified, until all amines have paired up. Over years of testing we have found that two weeks of curing at room temperature, which we define as 72°F (22°C), is a good indication of its full strength. Continue reading
By Tom Pawlak
G/5 Five Minute Adhesive is a fast curing two-part epoxy that allows 3-5 minutes of working time. It has an ideal viscosity which allows it to penetrate porous surfaces yet is viscous enough to bridge gaps when gluing broken objects. It adheres to a number of surfaces including wood, ceramic, metal, leather, plaster, stone, fiberglass, glass, cork, some plastics and paper. G/5 is an excellent choice for quick repairs around the house, high-end crafts and much more. Continue reading
by Grace Ombry
WEST SYSTEM®, Chesapeake Light Craft (CLC) and nine family groups joined forces at the 2010 WoodenBoat Show at Mystic Seaport in Connecticut this June to build nine Sassafras 16 kit canoes. With only a blue and white striped rental tent to shield them from the unseasonably hot weather in Mystic that weekend, everyone labored hard to get their boats a long way toward completion in just three short days. Continue reading
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
At two-part adhesive in a convenient, self-metering cartridge for permanent, waterproof structural gap filling and gluing.
Six10® Adhesive gives you the strength and reliability of a two-part WEST SYSTEM epoxy with the convenience of a single part product. Six10 is dispensed with a standard caulking gun. Non-sagging Six10 bonds tenaciously to wood, metals, fiberglass and concrete. It cures in temperatures as low as 50°F. Working time is 42 minutes at 72°F. Cures to a solid in 5–6 hours and will take high loads in 24 hours. Cure time is faster at warm temperatures and Continue reading
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 Continue reading
By J.R. Watson
The WEST SYSTEM® Six10 cartridge is comprised of the cartridge body, removable nose plug and a threaded retaining nut. A 600 static mixer is included with the cartridge. (It’s called a static mixer because it has no moving parts.) The cartridge fits into any standard caulk gun—manual, cordless or pneumatic—and allows simultaneous dispensing and mixing of the two-part epoxy. Manual caulking guns are graded by mechanical advantage (MA) in relation between the travel of the pistol grip and the plunger. When using he static mixer, resistance Continue reading
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 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.
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.
GLUING PLASTIC WITHG/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 and splits 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.
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.
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.
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 we send them 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.