Category Archives: Techniques & Tips

Six10 Thickened Epoxy Adhesive

Practical Tips for Using Six10

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

Testing, Testing, 123

By Julie Van Mullekom

By now most of you know that we are the manufactures of WEST SYSTEM® Epoxy. But you may not know what is involved in the manufacturing and more specifically, the formulating of WEST SYSTEM. It’s not just slapping some chemicals together and then packaging it up into a pretty box. To date we have performed thousands of tests, generating thousands of test results. 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

Toughness of G/flex Epoxy

Fasteners Demonstrate G/Flex Toughness

By Randy Zajac

It all started when I got a tech call from somebody asking if WEST SYSTEM® 105/206 would accept a nail pounded in, after it was cured, with no pilot hole. I confidently said that it would not work well and in most cases cause a fracture in the epoxy. Just for fun, I went out in the shop and tried it because even though every tech advisor agreed it wouldn’t work, nobody had ever actually done it. Well, we were right—the nail caused a “brittle” failure.

Then I saw a 1/8″ thick piece of cured G/flex 650 epoxy sitting on my work bench that I had Continue reading

G/flex 650 and 655 Epoxies

Mixing G/Flex With Other West System Epoxies

By Jeff Wright

WEST SYSTEM 105 Resin-based epoxy is a very versatile system. For years, experienced users have been blending the various products in countless ways. For example, users may blend 205 Fast Hardener and 206 Slow Hardener to make a hardener with a modified cure speed. Different uses of 410 Microlight® Filler provide a further example. Many customers assume that the only use of 410 is to make a fairing compound—it is added to thicken epoxy to a peanut butter consistency to create a light, easily-sanded filler. However, 410 Microlight can be used in other ways. Jon Staudacher in Epoxyworks 22 described how he applied a “runny” mixture of epoxy and 410 to fill the weave on a composite part and reduce the Continue reading

Moisture Exclusion Effectiveness (MEE)-comparison

Moisture Exclusion Effectiveness

By Bruce Niederer

I get mad at my computer fairly often these days when it takes more than a few seconds to open a file from an obscure site on the other side of the planet. Who has that kind of time to waste? Don’t even ask about photo files. There’s no point in arguing about it—we live in an accelerated world. We hate waiting for anything. Putting the social implications of this aside, a business involved in technical applications and products cannot afford to wait for real time field test results. We need data and we need it yesterday!

The focus of this article on accelerated testing will be how we test the ability of a coating applied in a relatively thin film to resist water transmission. This test is called Moisture Exclusion Effectiveness (MEE). It is based on a method developed by the 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

Understanding Flexible Properties

By Jeff Wright

The Technical Staff at Gougeon Brothers, Inc. regularly discuss material properties in a variety of applications. For example, it is not uncommon for us to discuss with a customer how to use carbon fiber to stiffen a structure, such as the shaft of a kayak paddle, and then within minutes discuss with another how to bond a dimensionally unstable wood, such as oak, and ensure precautions are taken so that the relative movement of the wood will not cause a failure.

For the kayak paddle, the customer’s concern is that the epoxy will allow the stiff carbon fiber fabric to be as rigid as possible. For bonding the unstable wood, the Continue reading

Positive displacement epoxy pumps

Tools for Measuring Epoxy Quantities

303 and 305 High-Capacity Positive Displacement Pumps

 
305 Metering Pump

 

 

 

Updated Spring 2016

For measuring epoxy accurately, Gougeon Brothers, Inc. has introduced high-volume epoxy pumps that are extremely robust. These pumps dispense epoxy faster than any pump the company has previously offered.  The 303 and 305 Positive Displacement Pumps work by trapping a fixed amount of resin and hardener, then forcing (displacing) that trapped volume into the discharge pipe or system.  The mechanics of this setup mean that increases in resin viscosity due to temperature changes will not slow dispensing speeds. Positive latching lids help prevent contamination of resins and hardeners.

The new 303 Positive Displacement Pump is calibrated for WEST SYSTEM 3:1 ratio epoxies (105 Resin with 207 Special Clear Hardener or 209 Extra Slow Hardener) and is easily identified with a red base. The new 305 Positive Displacement Pump is calibrated for 5:1 ratio epoxies (105 Resin with 205 Fast Hardener or 206 Slow Hardener) and has a blue base.

Positive Displacement Pumps are also available with drum fittings.  These connect directly to WEST SYSTEM Resin and Hardener drums so there is no need to decant materials.  This setup conveniently streamlines the metering process for high-volume users, saving both time and money.