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G/flex is a new epoxy introduced by WEST SYSTEM in mid-June 2007 . G/flex is a tough, resilient epoxy engineered for a superior grip to metals, plastics, glass, masonry, fiberglass, and wet and difficult-to bond woods. It is currently available in two versions: G/flex 650 Epoxy, a two-part (resin and hardener) liquid epoxy, and G/flex 655 Thickened Epoxy Adhesive with a thickening agent already added. G/flex is easy to use with a simple 1:1 mix ratio. It has a long open working time of 45 minutes at room temperature. G/flex reaches a working cure in 7-10 hours and a full cure in 24 hours.

Even as we introduce the new G/flex, we want to emphasize that our existing WEST SYSTEM 105 Resin with any of our 200-Series Hardeners is hard to beat for versatility and reliability. WEST SYSTEM 105 Resin mixed with the appropriate hardeners and different additives allows you to create an epoxy for a variety of applications like gluing, sealing, fairing, and sheathing. No other epoxy is more reliable for such a huge spectrum of end uses.

However, as a marine-grade glue that can be mixed in small batches, G/flex offers important features.

  • Toughness and Flexibility G/flex has been toughened. This gives G/flex the ability to make structural bonds that can absorb the stresses of expansion, contraction, shock, and vibration. G/flex is resilient and impact resistant. With a modulus of elasticity of 150,000 psi (WEST SYSTEM 105 Resin/205 Hardener has a modulus of elasticity of 450,000 psi), G/flex is more flexible and can deflect further than WEST SYSTEM 105/205, while being much stiffer than typical adhesive sealants.
  • Bonds to wet and damp surfaces G/flex has the ability to glue damp woods. It can be used on wet surfaces, even underwater when applied with specific techniques.
  • Excellent adhesion to hard-to-bond woods G/flex adheres tenaciously to difficult-to-glue hardwoods, both tropical and domestic varieties. This is important since many of the exotic and tropical species now being used to replace traditional woods present bonding challenges.
  • Bonds well to a variety of materials G/flex is ideal for bonding a variety of materials, including dissimilar ones. G/flex has a superior grip so that it can be used to bond to metals, plastics, glass, masonry, and fiberglass. G/flex is ideal for repairs to aluminum boats and polyethylene and ABS canoes and kayaks. It can also be used to wet out and bond fiberglass tapes and fabrics.
  • Ease of use G/flex is a simple two-part epoxy system. Resin and hardener are mixed in a 1:1 mix ratio by volume. For added convenience, a pre-thickened version, G/flex 655 Thickened Epoxy Adhesive, is also available. G/flex provides a relatively long open working time of 45 minutes. It cures in 7-10 hours and can be used in cool temperatures. Because it is simple to mix and use, G/flex is an excellent starting point for customers new to epoxy use.
  • Versatility G/flex can be modified with WEST SYSTEM fillers and additives if you need to meet particular bonding needs. Adding G/flex to other WEST SYSTEM epoxies can improve their toughness and flexibility.

Development of G/Flex Epoxy
G/flex is the result of years of WEST SYSTEM experimentation to develop a formula for a toughened epoxy. We wanted something that was simple to use, viscous enough not to drain out of a joint, and adhered tenaciously to a variety of materials under difficult conditions. However, material properties of an epoxy form a complicated web. When you formulate for specific end properties (like high elongation), you usually have to give up other properties in order to achieve it. Some of us thought that if you formulate an epoxy with five to six times the tensile elongation of WEST SYSTEM 105 Resin with any of our 200-Series Hardeners, the new product would be poor at dealing with constant or long duration loads. Yet when we tested G/flex under long duration loading with our exclusive Creep Test, it performed admirably--nearly matching WEST SYSTEM 105 Resin and our 200-series Hardeners. We worried that an epoxy with this much elongation is likely to perform poorly in heat resistance. Yet ASTM-D648 (Heat Deflection Under Load or HDUL) revealed G/flex performed even better than WEST SYSTEM 105 Resin with our 200-Series Hardeners. (G/flex like all WEST SYSTEM resin/hardener combinations can handle temperatures up to 200°F repeatedly but at this temperature will be more flexible and less strong than at room temperature. It returns to full strength as it approaches room temperature.) Well, what about through cure? Usually flexible systems take days to achieve the majority of their physical properties. Our testing revealed that G/flex’s 24 hour through cure is similar to that of WEST SYSTEM 105 Resin and 205 Fast Hardener. When we asked our chemists how that can be given that G/flex has a longer pot life than WEST SYSTEM 105 Resin and 206 Slow Hardener, they just smiled and said, “It’s magic.”

Adhesion Testing
How does G/flex adhere to woods and metals? Adhesion testing using the PATTI (Pneumatic Adhesion Tensile Test Instrument) on the same pieces of wood (with the wood sanded parallel to the grain with 80-grit sandpaper but no solvent wash) revealed that G/flex adheres to wood at least as well as WEST SYSTEM 105 Resin with our 200-Series Hardeners. With hardwoods and the often difficult to glue species such as white oak, Ipe, teak, greenheart, purpleheart and salangan batu, G/flex performed as much as 30% higher.

Adhesion testing with G/flex epoxy on metals also yielded excellent results, typically exceeding the adhesion results achieved with WEST SYSTEM 105 Resin and our 200-Series Hardeners.

We also discovered that 655 G/flex Thickened Epoxy Adhesive adheres to wet and damp surfaces admirably well. Obviously gluing to wet surfaces, especially when dealing with absorbent substrates like wood, is less than ideal because water is taking up the spaces where epoxy otherwise would find its way in; however, G/flex worked surprisingly well. Technique plays an important role in how effective a wet surface adhesion (even underwater repairs) will be. To displace the water to ensure a good bond, pre-thickened 655 G/flex Adhesive (or 650 G/flex that has been thickened with 406 Colloidal Silica to a toothpaste consistency) is needed.
G/flex kit instructions include a number of short “how to” sidebars on gluing to damp and wet surfaces, performing underwater repairs, and repairing plastic boats including crack repairs and making skid plates for worn ends on plastic canoes.

Using G/flex to expand the versatility of the WEST SYSTEM product line
G/flex can also be used as an additive for WEST SYSTEM 105 Resin with our 200-Series Hardeners. Adding it to WEST SYSTEM 105 Resin with any of our 200-Series Hardeners epoxy improves toughness and tensile elongation. Using it this way expands the utility and versatility of the WEST SYSTEM product line even further.

G/flex can also be used with WEST SYSTEM G/5 Five-Minute Adhesive to extend the working time. The more G/flex added to G/5, the slower the cure and the tougher the cure properties become.

When do I use WEST SYSTEM 105 Resin and the 200-Series Hardeners?
With all the attributes and improved properties of G/flex, you might be asking yourself “when do I use WEST SYSTEM 105 Resin and the 200-Series Hardeners?” The answer is that G/flex can’t do some things as well as WEST SYSTEM 105 Resin and our 200-Series Hardeners.  Examples include barrier coating and fiberglassing with heavier fabrics. Although G/flex flows nicely when spread out on a surface, it is less than ideal as a coating because of its higher viscosity. WEST SYSTEM 105 Resin with any of our 200-Series Hardeners is better for wetting out fiberglass cloth, and our 207 Hardener works especially well for clear finish projects like wood strip canoes and kayaks. WEST SYSTEM 105 Resin with any of our 200-Series Hardeners is also a better base for creating fairing putties because its lower viscosity allows you to add more low-density filler to it. This translates into a fairing putty that sands and carves more easily because of the higher filler loading.