JB Weld: Duct Tape in a Tube

Product Review

JB Weld: Duct Tape in a Tube?

"What is he talking about? How could any product be compared with the time-honored-fix-everything Duct Tape"? Even as I sat down to write this review, I had my reservations about drawing a comparison to the most used product in the U.S., but... when it comes to tractors, you have to face it... Duct Tape begins to lose it's usefulness. How about a replacement that handles the short term and permanent? There is a product that is used on nearly every tractor at one time or another and for which people seem to find no end to its applications. It can be used like Duct Tape to make quick repairs but unlike Duct Tape it can also make permanent long term repairs and solve problems that could not be conveniently solved any other way. Those with a history of working on tractors will have already guessed that I am talking about JB Weld (Oh Ok, it comes two tubes, not one, but the title sounded better that way).

JB Weld is basically an epoxy glue that does an exceptionally good job of bonding to cast iron and steel along with several other materials. As I mentioned, it is so common that I have yet to buy a tractor that did not have JB Weld used somewhere. It is sometimes used so well you can't tell its there and other times used as a sloppy quick fix. Finding where and how it can be used correctly is key to whether you are using it as an "inelegant hack" or an integral solution to difficult and expensive problems.

The Making of a Believer

Somehow I managed to get through 35 years without ever using or thinking about JB Weld. I came across it on my first serious working tractor. In wanting to get the machine working and looking perfectly so I could "just use it" for many years, I tore apart my newly purchased machine and began to use an angle grinder with wire brush (this is prior to the day I discovered the sand blaster) to take off 40-plus years of paint in preparation for putting on new coats. As I was taking the torque tube down to bare metal, I came to a place where it felt and looked different. To my amazement, someone had plugged, with a gray epoxy, what appeared to be a casting-flaw-gone-bad or where possibly the Power-Director (Allis Chalmers late 50s hand clutch) had come apart and spun a component through the casting. It was a small one-quarter inch hole and the job was so good that it had never leaked nor, due to careful finishing, was it visible until I removed the first coat of paint. This was not only my first experience with metal epoxies but also tainted my viewpoint to the plus side of using them. I figured "It has been there at least 15 years and hasn't failed so what the heck", I carefully sanded off the wire brush marks and painted over it. Obviously, this was an example of an appropriate use of the product and a good job to boot. Practically speaking, replacing the torque tube would have been not only extremely expensive but would have been difficult to locate. This repair was in a non-stressed location so it worked and could be called permanent.

This experience was followed by a succession of other experiences that made me realize that not all JB Weld repairs were handled so professionally. It is not so much where I found it used as it is how the jobs were done. Clearly if an epoxy repair has lasted many years, it is being used in the right place and the surface had been prepared correctly. If not it would have broken or cracked and would not be present on the tractor I purchased. Simple logic right. The most common problem is sloppy application and finish work that makes the repair obvious and for those of us coming along later means redoing the work or replacing the component. More on that later. In using the product, you need to think about:

  • Where should it be used (and a close relative, What it can't do)
  • How should the surface and epoxy be prepared
  • How should it be finished to be imperceptible to the eye while remaining strong

Where will it work? (where will it fail?)

Listing off all possible uses for JB Weld is a futile gesture since it bonds to darn near everything. The key to finding good applications, is stress. Is the part stressed? If so, you better consider real welding since the chances are good that it will fail. I did several tests in my "laboratory" (I mean the laboratory with the big barrel wood stove, greasy concrete floor and tools scattered in every nook and and cranny). I knew that JB Weld would work fine in any unstressed steel or cast iron hole-filling application, but would it work on moderately stressed components. I decided to see how it would work in mating two chucks of light bar stock by carefully preparing the surface, evenly spreading the epoxy on a three-inch overlapping area of both chunks and then allowing it to sit smashed in my vise for two days. The results were surprising in that I could not break the bond with my hands even when placing one end in the vise and pulling hard on the other. This bond was still short-lived since the next test involved grabbing the 36 ounce ball pein off the wall and ferociously attacking the side not in the vise. It broke right off after 2 hits. There was a purpose to this test. Ford Balers from the mid-50s to the mid-60s used a nut with handle welded on that turns down a spring to pressure the bale chute. This keeps pressure on the bale while it is being formed. I did this test to see how well JB Weld would hold at hand pressure and possibly allow me to put the nut and handle arrangement back together. When bonding the handle to the bolt, I could easily break off the handle. What I concluded from all this was that any application involving light stress would most likely succeed if there was sufficient surface area to the bond (Ok, maybe I am bit slow but the test was valuable to me in understanding the product). You might think that the above rules out bonding any two pieces of steel that are perpendicular but not so, I have seen several examples contrary to this that work fine. Again it is the surface area and successful use involves building the bead (just like real welding) out in a 45 degree angle. There is an example of such successful use below (gas tank mount).

Here is a woefully inadequate list of possible uses:

  • Plug a Radiator hole - on a working tractor this is a good fix that will tide a radiator over until you finally replace it. Seams begin to get "iffy" but I do have one that doesn't leak with a repair on a seam (or was it the "stop leak" that keeps it from leaking).
  • Steering wheel - This was a real surprise. If the steering wheel coating is simply cracked where the spokes meet the wheel, you can fill the cracks in, sand it down and avoid a major recovering. This works well and as a side benefit, if you don't want to paint it, the JB Weld tends to take on the black of the cover as you sand if sanded while drying (give it several hours). The end result looks like a recover job.
  • Gas Tank - Even when coating the inside of the tank with tank sealer, I like to first plug the pin holes from the outside with JB Weld. Another use on the tank is to put the mounts back together on a working tractor. I have an early Allis Chalmers C that uses the mounts protruding from the bottom of the tank at a right angle. The previous owner obviously did not want to weld the tank (for good reason) and used a healthy bead of JB Weld to bond the mount back on. It works and since it can't be seen is a good alternative to attempting to replace the more rare early tank (the more common later ones use only a top mount).
  • Engine Blocks - Along with my torque tube example above, the Cast Iron engine block can be epoxyed with JB Weld. I had a Case VAC with a freeze crack on the side. The previous owner had ni-rod welded the crack. It always seeped anti-freeze when hot. An Allis Chalmers C with a similar crack had been JB Weld'ed, it didn't leak. Realistically, I would have used the Ni-rod followed by brazing as my first choice but point is the JB Weld worked.
  • Carburetors - Carb bodys are expensive. If you crack one that is otherwise good, this is worth trying since it can't be used as a trade in anyway. The JB Welded carb I have works fine. Someone overtightened the incoming gas fitting and cracked it. They JB Welded the crack and as long as non-hardening Permatex is used it seems strong enough and does not leak.

As I said, this is not a complete list but may give you some ideas. As you may have noticed, even if an epoxy repair will work, there are sometimes better approaches such as mentioned with the engine block crack. Another good example that I have is a manifold that has been filled. It seems to handle the heat but any unforeseen stresses on a component with that much heat expansion will likely cause a leak. Real welding would be a better choice. Here is a "Nevers use it for..." list that goes beyond avoiding stressed repairs:

  • Components that spin - Never epoxy anything that may fly off if it fails. For example, you might use it on a pot-metal governor case but never on the governor fly-weight mounts.
  • Components that relate to safety - Never epoxy safety or protection guards. Things like PTO guards must be truly welded.
  • Weight Bearing Components - If it bears weight, use a real weld, especially in cases where suspension is involved. It won't be satisfactory anyway, so why risk it.


"Clean and Dry Surface". That's what the instructions say and I will add "take it to Bare metal". JB Weld will adhere to paint, but the paint will come off taking the bond with it! Make sure you take the surface to be bonded right down to bare metal. Cast Iron is even more difficult since it is porous and traps oil and dirt in the pores. Degrease the surface to ensure that you get a good bond and with cast iron, heat it up to open the pores and allow a thorough degreasing. You can figure that you should spend at least 10 times as long preparing the surface as you will actually applying the JB Weld (applying it only takes seconds anyway).

Mixing up the goop is easy. Equal parts hardener and bonding agent. Make sure you mix these on a hard non-porous surface (a clean and dry plastic coffee can lid works great) that won't "contribute" new elements to the mixture (e.g., mix up the JB Weld on a piece of wood and you will be including sawdust in the bond). Once mixed, application is easy. Again use a non-porous plastic tool of some kind to apply. The trick will be using as little as you can get by with and as much as is necessary for strength. Obviously on joining right-angled materials such as the tank mount mentioned above, you will have to use a significant amount to build a bead and get sufficient surface area covered. Since you will have to sand off any rises and bumps, try not to create them in the first place. Application at the recommended ambient temperature will help to insure that such bumps and rises smooth out during drying, but try to keep them to a minimum. If at all possible, best results will be achieved with items that can be held together under slight pressure for the first 24 hours. Be creative with wood working, strap, or bar clamps. It can help.

Finish Work

This is where most uses of JB Weld seem to fall down. I assume that since folks think they are doing a quick fix, there is no reason to clean up the surface when done. Welders take pride in their work, applying a bead without spatter, attempting evenly spaced circles from the molten pool, eliminating all slag, redoing holes that form, and even using an angle grinder to clean up spots that may look bad. If you are trying to use JB Weld as a permanent fix, you should do the same. The tools are a file and various grades of sandpaper. If possible the end result should be nearly undetectable though in practice many applications require that you leave a bit of material protruding. Even so, the surface can be made smooth and even.

Knowing when to use it and when to go to the welder is important. Also keep in mind that the purpose of the tractor impacts whether it is appropriate to use this type of repair. Spending $20,000 on a perfectly restored rare antique tractor may not jive with doing a epoxy weld. Use it correctly and appropriately and it will rank highly as an important weapon in your arsenal for keeping a tractor working.

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