G/Flex Vs JB Weld: What’s The Difference?
Both adhesives boast serious gripping power. For waterproof wood work, G/flex has the history and specialty. But JB Weld’s speed and strength makes it ideal for multi-material repairs. I took these two contenders through their paces – here’s my take on when each adhesive has the edge.
- G/Flex Vs JB Weld: Specs & Uses
- My Hands-on Test: G/Flex 650
- My Hands-on Test: JB Weld Plastic Bonder
G/Flex Vs JB Weld: Specs & Uses
⏰Cure Time
G/Flex: 7-10 hours
JB Weld: 30 minutes
🆚Heat Deflection Temperature
G/Flex: 127°F
JB Weld: up to 250°F
🛠️Common Uses
G/Flex repairs broken headphone headbands; fills and seals holes in plastic kayaks; Fixes mounting issues on carbon fiber mountain bikes; seals seams in aluminum boats; fixes vacuum cleaner cord.
JB Weld repairs high-density polyethylene (HDPE) tanks; bonds plastic nameplates on car trunk lids; Repair plastic car bumpers; fills stripped holes in plastic.
Technical Info
My Hands-on Test: G/Flex 650
✅Pros: G/Flex
Now, let’s talk about the versatility of this epoxy. (Glue Damp Woods, Wet Surfaces)
Versatility
One of the standout uses was when I repaired a hole in a plastic kayak. I was impressed by how well it held up, even when exposed to water. And believe it or not, it even came to the rescue of my carbon fiber mountain bike. I had a derailleur mount issue, and this epoxy fixed it without a hitch. Months have passed, and the repair is still going strong. I can confidently say that this epoxy is a reliable solution for various repair needs.
Repair a Delaminated XC Ski
The first time I used it was to repair a delaminated XC ski. Mixing and using it was reasonably easy, and the result was a tough and flexible fix. The long working time was a plus, although it meant I had to weight or clamp 
the work piece. Trimming and sanding the overflow was surprisingly straightforward. Encouraged by this success, I decided to tackle the broken headband on my son’s large headphones. Despite not being able to get a lot of epoxy into the broken area, I took the chance. To my delight, after several weeks of heavy use, it’s still holding well.
Strength and Bond
The strength and bond this epoxy provides are remarkable. When I used it on composite kayaks, the bond was potentially stronger than the laminate itself. It’s truly amazing stuff! Plus, it’s not limited to specific materials. This genuine epoxy bonds well to many different materials, making it suitable for a wide range of repair projects.
Ease of Use
In terms of ease of use, I found this epoxy to be strong and easy to work with. The 50/50 mix ratio takes away the hassle of figuring out the right proportions. I marked the bottles and poured an even amount from each, making the mixing process a breeze. The long cure time was a definite advantage, allowing me plenty of time to work before it set up. Additionally, the semi-hard state it spends time in was surprisingly easy to trim and smooth with a knife or razor.
A Little Tip
If you’re looking to enhance the performance of this epoxy, I highly recommend using a filler
like microlight. Not only does it improve the bond, but it also reduces sag and running, fills voids, and ultimately reduces the amount of epoxy needed for a job. It’s a cost-effective solution that enhances the overall result.
❌Cons: G/Flex
But let me tell you, I just wish the epoxy was available in smaller bottles. I don’t use it frequently, and most of the time, I only need a small amount. The 4oz bottles are just too much for my needs, although I must admit they do seal well.
FAQ: G/Flex
Q: What surface area can I cover with an 8 oz bottle? And approximately how many rivets can I cover with it?
A: The coverage area of an 8 oz bottle can vary depending on different factors, so it’s a subjective question. However, if used conservatively, it can easily cover more than 100 rivets.
Q: What is the recommended temperature range for applying G/Flex? I’m concerned about it hardening too quickly in warm weather while repairing a canoe in July.
A: I have used G/Flex at temperatures around +2°C and above. It takes a long time to dry, approximately an hour to set, and nearly 24 hours before it can be handled with confidence.
Q: I applied the epoxy, and it has hardened and cured. Now, after several days, I want to apply another layer. Is it possible to do so?
A: Yes, you can apply another layer. Make sure to clean the surface from any oil using 202 or acetone. You can also roughen it up with sandpaper before applying the additional layer.
Q: I removed an old transducer from the bottom of my fiberglass boat. Can G/Flex permanently fill and seal the resulting holes?
A: G/Flex epoxy is suitable for filling and sealing holes left by fastenings. However, for larger holes like the stem of the transducer, you may need to use
Bondo (bondo plastic metal instructions). Composite hulls typically consist of both fiber (glass or carbon) and resin. G/Flex epoxy only replaces the resin part, so for holes larger than 5 mm (3/16″) in diameter, both parts are required for a proper repair.
Q: What is the recommended ratio of hardener to epoxy for repairing a Royalex canoe?
A: The recommended ratio is a 50/50 mix of hardener to epoxy.
Q: Will G/Flex work for repairing a vacuum cleaner cord?
A: For repairing a vacuum cleaner cord, it’s recommended to use electrician’s tape, also known as black tape. There is also a liquid type available for such repairs.
Q: Can I dye G/Flex with black mica powder?
A: Adding black mica powder to the epoxy will give it a sparkling and shiny effect. However, if you want to dye or add color to the epoxy, you need to use a pigment.
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My Hands-on Test: JB Weld Plastic Bonder
✅Pros
It worked well and stuck firmly.
I wish I had a clamp to help with the application, but I managed without one. Any excess adhesive can be wiped off with an old damp cloth. So far, so good. I recommend this product, although I would have liked the applicator to be slightly larger.
Fix The Glass Door of the Toaster oven
I also used the adhesive on the glass door of our toaster oven, which had started to separate from the metal frame over the years. I applied about half an inch of the adhesive at the top of the door, and so far, it seems rock solid.
Fast Curing Time
It’s worth noting that the curing process begins fairly quickly, within about five minutes of mixing. So it’s important to have everything prepared and ready to go. To ensure a secure bond, I quickly taped the skirt down using several pieces of metal tape. Once in place, it was rock solid. After 30 minutes, I removed the tape, and the bond was incredibly strong.
JB Weld Vs Gorilla Glue
J-B Weld Original is steel reinforced, has a tensile strength of 5020 PSI and can withstand temperatures up to 550 degrees Fahrenheit (287 degrees Celsius); gorilla glue is nice for repositionable, gap filling, paintable, easy to dispense
Various Plastics
Now, let’s talk about the performance of JB Weld on various plastics. This product has an impressive ability to adhere to plastic surfaces. It’s not just for fixing broken plastic pieces; it can also be used to repair and rebuild parts or fill in missing sections. The viscosity of the product allows for easy application with minimal spillage. As it gradually hardens, it can be repositioned and adjusted.
❌Cons
It comes in a syringe-like tool and requires the mixture of two liquids. I found it easy to use, although it’s important to have a spare surface for mixing, like an old container. You can’t use it straight out of the tube; it needs to be mixed.
FAQ
Q: Will JB Weld be effective for repairing small gaps in an outdoor carpet that was installed with slight spacing between sections?
A: I have not personally used it on carpet, but Henry’s adhesive is highly recommended for carpet and has proven to be very effective in my experience.
Q: If I apply JB Weld to a large hole, will it be possible to drill into the cured adhesive in order to insert screws?
A: Once JB Weld has fully cured, it can be drilled and tapped to accommodate screws. However, the strength of the bond between the JB Weld and the hole will depend on how well the hole was prepared before applying the adhesive.
Q: Which adhesive is recommended for bonding a plastic nameplate back onto the trunk lid of a car?
A: In my experience, polyurethane adhesive like 
Sikaflex 291(3m 5200 vs sikaflex 291) has been the most effective option for bonding plastic nameplates back onto car trunk lids.
Q: Have users encountered any issues with JB Weld’s longevity on plastic car bumpers? Is an adhesion promoter necessary?
A: Users have reported successful repairs on plastic car bumpers without the need for an adhesion promoter. JB Weld is capable of providing excellent bonding for bumper repairs.
Q: Is it possible to bond leather using JB Weld?
A: While I have successfully used this product to bond plastic-to-plastic and plastic-to-metal, I have not personally tested it on leather. It is crucial to maintain a stable bond for at least 5 minutes.
Q: Although it is an adhesive, I would like to use it to fill a stripped hole in plastic and then drill a new hole for a screw. Is JB Weld suitable for that purpose?
A: Once JB Weld sets, it becomes similar to hard plastic. Although I have not attempted to drill through it, it appears feasible. I would recommend starting with a small drill bit for the initial attempt. Alternatively, you could apply the plastic bonder with the screw already in place, using oil or grease on the screw to facilitate its insertion.
I’m Ronald Stevens, a Mechanical Engineer obsessed with adhesives, glue, and all things sticky! My passion began in childhood when I’d always be the one playing with glue during arts and crafts. And I’d spend hours researching and experimenting. Happy reading, and remember: stick with the best, and you’ll never be stuck in a mess!
Feel free to contact me and join our discussion:
After G/Flex cures, does it have a rubbery or firm texture?
Once cured, the epoxy hardens into a firm coat. The hardness of the coat can vary depending on the mixing ratio. It offers flexibility and holds together well. If you use less hardener, it will provide more flexibility in the coverage. It has been successfully used to repair bows, yielding good results.
How can I ensure that paint adheres well to JB Weld? Currently, the paint tends to come off when scratched.
The approach to achieving paint adhesion may vary depending on the intended use of the JB Weld. However, if you desire a smooth surface for painting, it is recommended to apply a primer after using the JB Weld. This is a technique my father employed for his lawn mower with satisfactory results.