JB Weld Epoxy Review and Guide

JB Weld Epoxy Review and Guide
By Bill Wyatt
November 6, 2020
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J-B Weld can be found in every mechanic’s toolbox. There’s no better way to repair metal without welding.

Let’s take a look at this unique and interesting adhesive and see what it’s capable of.

Quick Overview

JB Weld is a steel reinforced two part epoxy resin which once cured forms a permanent bond. 

It’s one of the best ways to repair metal (other than welding) but it also works on other materials including plastic and wood. 

J-B Weld works on most surfaces, forming an extremely tough and permanent metallic bond, which can withstand high pressure and extreme heat, making it perfect for automotive repairs, even in the engine.

Once cured, J-B Weld can be ground, filed, painted and drilled just like a regular metal.

Pros

  • Easier than welding
  • Works on more than just metal
  • Metallic color (silver/grey)
  • Extreme temperature resistance
  • Can be ground, filed or drilled like metal
  • Resistant to Gasoline and Oil
  • Non Toxic
  • Cheap to buy

Cons

  • Takes a while to cure
  • Does not bond certain plastics
  • Does not bond to flexible materials

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Product Features

J-B Weld is a useful tool to have around the house as well as in a garage or shop.

The unique strength and durability of J-B Weld make it extremely versatile, used in everything from plumbing and marine repairs to arts and crafts. 

J-B Weld is able to handle some projects that a regular glue just wouldn’t be able to handle, such as engine case repairs – thanks to the steel infused formula providing a solid and temperature resistant final cure.

Easy to use (Much easier than welding!)

J-B Weld is a little bit more tricky than some other adhesives, especially because you need to prepare the surface quite thoroughly, but it’s a lot easier than welding.

Forms a permanent bond

Once J-B Weld cures, it becomes a permanent bond. 

The only way to remove it after it’s cured is to grind it away with a drill or a dremel tool.

It’s as strong as metal and just as durable.

Extreme temperature resistance

The reason auto mechanics love J-B Weld. It won’t melt when used in high temperature engine repairs or other high heat projects.

J-B Weld can withstand constant high temperatures of up to 550ºF (287 ºC) once it’s fully cured.

As well as high temp, J-B Weld has also been tested all the way down to -67 ºF (-55 ºC), so it’s great for outdoors and indoors use alike, even in the winter.

Super durable and versatile

Once cured, J-B Weld is waterproof, extremely temperature resistant, electrically insulating, and will not degrade when exposed to petroleum products (including gasoline, diesel, and engine oil) and most solvents.

Even acetone, which is used as a solvent for most adhesives doesn’t degrade J-B Weld.

In fact, the only way to remove J-B Weld is mechanically.

It’s perfect to use outdoors or indoors, in any conditions.

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How to use JB Weld (Instructions)

J-B Weld is simple to use, but there are some important steps you need to follow to prepare the surface, otherwise you’re going to end up with a weak bond.

1: Prepare the surface beforehand

Especially with automotive repairs, it’s important to remove any oil, paint, dust, dirt or moisture from the surface before you apply any J-B Weld.

Use rough grit sandpaper or a grinding tool to grind the surface down to bare metal.

Use acetone, isopropyl alcohol, or some other degreaser for the best results.

JB Weld is permanent and a pain in the behind to remove, so make sure you don’t skip this step so you get a good strong bond first time.

For non-metallic surfaces, use sandpaper to roughen smooth surfaces as this will provide better adhesion.

2: Mix the two parts in a 1:1 ratio

Open both tubes and squeeze them out on to a disposable surface. A scrap piece of cardboard or plastic will be fine.

Mix the white and black tubes together with a disposable mixer until it’s a uniform dark grey color.

Whatever you use to mix it up will be ruined, so don’t use your wife’s cutlery! Use an old scrap piece of wood or a matchstick or something.

3: Apply the epoxy in an even coat

Apply the JB Weld to the surface(s) you are going to repair.

After you’ve mixed the J-B Weld, you’ve got around 10 minutes before it starts to become tacky, so ensure your repair is in the correct position straight away before you leave it to cure.

J-B Weld can be used to repair cracks or leaks, or to bond separate parts together.

4: Allow 15 hours for the bond to cure

J-B Weld will be dry enough to handle after 4-6 hours, however the manufacturer recommends you leave at least 15 hours before putting any repaired object back in to regular use, to ensure the bond has a chance to fully cure.

J-B Weld is quite runny, so you may wish to position your repair in a way that prevents runs. (Or place down a newspaper to catch any drips and prevent mess)

What is JB Weld used for?

J-B Weld is best for metal, but it works on other materials too including wood, brick, concrete, and fiberglass.

It won’t work well on plastic, leather, rubber, vinyl or any other flexible and/or oily surfaces.

J-B Weld is good for:

  • Wood
  • Concrete
  • Brass
  • Iron
  • Brick
  • PVC Plastic
  • Stone
  • Aluminium
  • Fiberglass
  • Ceramic
  • Copper
  • Plus most other metals

It’s not great for:

  • Polyethylene and Polypropylene Plastics
  • Flexible materials like leather or rubber

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FAQs

Does JB Weld work on Aluminum?

Whether you’re bonding aluminum to steel, aluminum to aluminum, or aluminum to any other metal, JB Weld has you covered.

Most cast aluminum repairs are easily fixed with JB Weld, without the need for welding equipment.

JB Weld Cure Time / Dry Time

JB Weld will be tacky within about 20-30 minutes, depending on how much you used.

Once it gets to this point, you can mold it with a suitable tool and it will stop running.

The drying time for JB Weld is around 4-6 hours until it becomes solid enough to handle, however the cure time is from 15 to 24 hours, depending on how much you use and the humidity and temperature when you apply it.

JB Weld cure time vs temperature:

You can decrease the cure time by increasing the temperature of your working environment. JB Weld works best at room temperature, so if possible keep your repairs indoors if the weather is cold until it gets a chance to cure.

Is JB Weld Conductive? (Does JB Weld Conduct Electricity?)

In spite of being partially made from steel, JB Weld is an electrical insulator, meaning it does not conduct electricity.

I was surprised to learn this when I was researching this article. I had always assumed JB Weld was a conductor like steel, but it turns out the epoxy resin the steel is in is an insulator, and there is a lot more resin than there is steel, so the final cured JB Weld is not conductive.

Does JB Weld work on Copper?

JB Works well on Copper, but it’s important to note it will be very visible on Copper, as it dries a dark grey color once it’s fully cured.

Copper is often used in electrical applications, so (depending on your project) it may also be important to keep in mind that JB Weld is not conductive.

JB Weld for Exhaust repairs?

JB Weld is great for automotive repairs, but it may not be the best tool for an exhaust repair.

The manufacturer specifically advises against using JB weld for exhaust repairs, however depending on the nature of the repair it can be a good temporary solution until you can replace or have your exhaust welded.

JB Weld can deal with extremely high temperatures, up to 550 ºF, so for any car or truck, no matter what the model is it’s going to be perfect for repairing small holes or cracks in your exhaust tailpipe.

Where it might not be a great idea to use JB Weld is when you have a broken exhaust manifold or catalytic converter, which can get extremely hot in some engines, hot enough to weaken the strength of the bond JB Weld creates.

Is JB Weld suitable for Plastic?

JB Weld can bond some hard plastics like PVC and solid polystyrene (Not polystyrene foam), but it can’t bond any flexible materials, or any oily plastics like HDPE/LDPE (Polyethylene) or Polypropylene.

JB Weld for Wood:

JB Weld works fine for wood, but it’s only really recommended where you have to attach metal to wood.

For wood to wood applications, you will get a stronger and more wood-like bond using a PVA wood glue. Some wood glues like Titebond III or Elmer’s Wood Glue MAX are also completely waterproof just like JB Weld and are easier to work with for woodworking projects.

Safety Data Sheet

If you’re looking for the MSDS Safety Data Sheet for JB Weld, I’ve attached a link to it below. 

JB Weld Safety Data Sheet (MSDS)

Can I use JB Weld for Gas Tank Repairs?

Gasoline, diesel and motor oil don’t degrade JB Weld once it’s cured, so it’s great for all kinds of auto repairs, however I would not recommend the average person even attempt to repair their gas tank with JB Weld.

Firstly, your gas tank is important. If the bond fails and your fuel leaks while you’re out driving somewhere, you could end up stranded or worse.

In an emergency, sure. It can be used to get you to the garage to get it welded or replaced.

How to Remove JB Weld

JB Weld advertise a permanent bond, and for once it’s not just marketing talk.

JB Weld really is permanent and there’s no easy way to remove it once it’s had a chance to cure.

Solvents don’t work on it, the only thing that works for JB Weld removal is some good old fashioned elbow grease.

If you need to remove JB Weld, you’re going to have to crack out the drill, dremel, sander, or file  just like you would with a metal.

JB Weld for Radiators

If you have a radiator leak and you need to repair it quickly, JB Weld is a great option.

While regular JB weld will be able to hold most repairs, JB Weld have a special kit specifically designed for radiator repairs (JB Weld Radiator Repair Kit) which is designed to fix holes of up to 3/8 inch diameter, or cracks up to 4 inches long. 

It’s a completely different product from regular JB Weld, it comes in a putty format with fiberglass cloth. You apply the fiberglass cloth first, and build up the putty over the top like you would if you were layering fiberglass with epoxy. 

The fiberglass gives the JB Weld more tensile strength, which is especially important in radiator repairs because of the high pressure.

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