Can you weld over rust? It’s one question most beginner welders ask. The good news is that welding rusty metal is possible. But the bad news is that the weld won’t look as aesthetically pleasing as welding polished steel. However, with the right welding rod, some patience, and a good welder, you can weld over rust to create a strong joint.
The truth is that welding rusty metal is challenging for any welder. But it’s a skill to learn. This is because sooner or later, you’ll be faced with a situation where you must weld metal that is rusty. Sometimes, you may not have the right equipment required to remove the rust to get the job piece back to bare metal. There is a limit to how much rust is acceptable, if the rust is more than .5mm thick I would advise not to proceed with welding this job.
But before you take the welding gun to weld a rusty work-piece, there are a few things to remember.
- The first is that you shouldn’t weld rusty metals for critical applications.
- Second, welding over rust creates more fumes.
- Lastly, don’t expect perfection.
So, now you know what to expect, let’s explore the best ways to make a successful weld over rust and get the best results. In addition, you’ll get the top “welding rusty metal” tips from the experts.
Can You Weld Rusted Metal?
It is possible to weld rusted metal if you clean as much rust as possible, use the correct consumables, and use the proper process. For example, welding rods 6010 and 6011 are the best ones to weld over rust. Also, use a stick or flux-cored welding techniques for the best results.
Of course, the answer to the question — “can you weld rusted metal?” — depends on the amount of rust. Ideally, you should clean the metal to remove the rust. But unfortunately, it will be impossible to fix the rust problem if the rust layer is so thick that there is little bare metal left. Additionally, you cannot, or should not, weld rusted metals if it’s for a critical piece of structural steel.
Can You Weld Over Rust Safely?
Stick or flux-cored welding is the way to go if you want to safely create a strong weld over rust. Therefore, when welding rusty material, don’t forget to wear safety gear — goggles, gloves, ear protection, and protective clothing. However, even more, important is excellent ventilation. Rods for welding rust emit lots of fumes.
Therefore, the best way to weld over rust safely is to remove the corrosion. You can prepare the metal with a wire brush to remove the rusty bits. Or, if it’s a thick piece of rusty metal, use a grinder or wire brush to expose as much bare metal as possible. Sometimes, you can weld over rust by cleaning the metal surface with acetone.
What 7 Problems Are Likely When Welding Rusty Metals
The problems with welding over rust can be lower tensile strength, poor weld, and a poor flow of electricity. Unfortunately, the issues when making a weld on rust will cause increased spatter and a stiff, slow puddle. You end up with a weak weld that also looks less than desirable.
But as the adage goes: “to be forewarned is to be forearmed.” So, you can make the best job of welding rusted metal by knowing the type of problems you’re likely to encounter.
Here are seven effects of rust on welding to look out for.
1. Rust in welded metal causes poor tensile strength
Welds on rusted metal won’t have the same strength as polished, bare metal free from contaminants. Rust is an iron oxide and creates oxygen in the weld pool. This causes a chemical reaction reducing the number of alloying elements in the weld.
2. Welding over rust can result in a lack of fusion
Another issue with welding rusted metal is that the two pieces of metal don’t fuse properly. The fact is that rust impedes heat and doesn’t allow the filler material to mix with the base metal. The result? A weak weld and superficial joint that will fail under pressure.
3. Rust in metal causes an unstable arc
Trying to weld over rusted metal results in lots of spatters due to an unstable arc. A smooth welding process requires metal pieces to be free from impurities. Contaminants on the work-piece cause an erratic arc. This has the effect of welding with lower amperage.
4. Trying to weld rusted metal causes poor electrical flow
Apart from causing an unstable arc, the rusty metal could prevent the arc from starting. Rust on metal causes corrosion, reducing the conductivity of the connection between the electrode and the ground clamp. And thick rust on the work-piece may mean it’s impossible to start the arc.
5. Rust in welds affects the weld puddle
Rust contaminates the weld puddle, which makes it difficult for the molten metal to flow smoothly. This means that the pool becomes stiffer and flows slower. To avoid this issue, decrease the welding speed or increase the amperage. Otherwise, the unsightly weld won’t fill the weld joint and will be narrow.
6. Welding rusty metal causes porous welds
The effect of rust in the weld puddle creates oxygen and microscopic bubbles. The result? The final bead will not be as dense as it should be and will have poor weld quality. This means that the joint can break easily under mechanical or thermal pressure — not something you want in critical pieces.
7. Welding over rust results in ugly welds
Trying to weld rusted metal is not great if you need to create an aesthetically pleasing weld. Apart from not being uniform, the bead will become discolored and bumpy and may have an asymmetrical, convex shape.
Preparing Rusty Metal for Welding
Preparing metal for welding is key to avoiding common issues when trying to weld over rust. What does preparation involve? It’s necessary to remove as much of the corrosion as possible. This increases your chances of a strong well that holds up under pressure and looks nice.
Your first task is to check the work-piece to assess the amount of rust damage. Typically, there are three stages in the rusting process. These range from superficial rusty spots to deep corrosion that has penetrated the metal plate. The extent of rusting determines your prep method.
Stage one rust:
You’re likely to see reddish-brown marks on the surface of the metal. These will be randomly distributed without any clear patterns here. Stage one rust is superficial, and you should be able to get rid of it without too much trouble. Using steel wool or a wire brush may be enough to clean the surface.
Stage two rust:
Rust has penetrated the surface, and slight scaling or peeling may be evident. There is usually enough unaffected base metal at this stage to weld the piece. Therefore, you should use a grinder or a wire brush to remove the scale from the surface of the work-piece.
Stage three rust:
The worst type of rust. This is where rust has penetrated almost the entire depth of the metal, and extensive scaling occurs. As a result, the metal piece may not be structurally sound. Depending on the thickness of the steel, the rust may cause partial or complete weakening of the metal. If you remove the corrosion completely, you might end up creating holes in the metal.
The most common tools you can use to prepare rusty metal for welding:
· Steel wool: This is typically used to remove superficial rust from metal. You can also use steel wool to polish metal and get it ready for welding after grinding it.
· Sandpaper: Sandpaper is excellent for getting rid of some rust before welding. However, it’s good to remember that it can leave scratches on the surface.
· Wire brush: This tool is ideal for removing light rust and preparing metal pieces for welding that show signs of scaling. You can use a hand wire brush or a motorized one.
· Angle grinder: An angle grinder is essential for any serious welder. You can use this powerful tool to remove rust entirely and smooth out rough edges. You could use a flapper disc for less aggressive but thorough cleaning.
· Sandblasting can be a great option for larger jobs although great care is necessary.
· Cloth and solvent: The last step in preparing rusty metal for welding is to clean the joint or welding surface with acetone or lacquer thinners. This ensures no oily residue could interfere with the welding process.
How to Weld Rusty Metal
Stick welding, or Shielded Metal Arc Welding (SMAW), is the best option for welding rusted metal. This is because stick welding uses flux-coated electrodes that burn through the rust. In addition, the welding rods for rusty metal contain de-oxidizers that help to neutralize contaminants in the weld.
Here are the basic steps to welding rusty metal:
Assess the metal: First, examine the metal to see its thickness, the extent of rust damage, and if there are other surface contaminants. It’s also crucial to make sure it’s structurally sound.
Preparation: Prepare the rusty surface for welding by cleaning the surface to remove as much rust as possible. If you can remove the rust entirely, you could then choose MIG welding.
Set the weld: Now that the work piece is ready for welding and you’ve cleaned as much rust as possible, it’s time to set your weld. So, clamp the work-pieces and put the ground clamp in place, ready for welding.
Make the first pass: Check the electrode to ensure you have the correct welding rod for rusty metal. Thinner electrodes are better for preventing burn-through on rusted metal. You’ll also need to check the amperage to ensure it is the right setting.
Check the integrity of the weld: After making the first pass, it’s vital to check the weld. You must look for signs of issues that commonly happen when welding over rust. Clean the bead with a wire brush and look for the following:
· 1/ Porosity: Are there small pinholes in the bead? If so, oxygen has compromised the weld. This means the joint is weak and fragile. You’ll need to grind the weld back and redo it.
· 2/ Penetration: Are there signs of good penetration? You can be happy if it’s smooth and uniform. But you’ll need to start again if the welding arc didn’t burn through or undercut the metal.
Make the final weld: If everything looks as it should, then you can make your final welds — happy in the fact that you know how to weld over rusted metal.
Welding Rod for Rusty Metal
Welding rods E6010 and E6011 are the hands-down best welding rods for welding rusty metal. These sticks are ideal because they have a high cellulose content (as indicated by the last two digits) and create a hot arc. In addition, these are fast freeze rods — not ideal for rust, but still the best type of welding rod for rust.
But there are a few things to remember when choosing the right stick electrode for welding rusty metal. First, the 6010 only runs on DC. So, check your welder has a direct current option. If your welder only has AC, then choose the 6011 electrodes.
Alternative welding rods for rusty metal include the following:
The disadvantage of these sticks is that they cannot weld thicker material with many layers of rust.
How to Repair Rusty Metal
To repair the rusty metal, you must remove all signs of corrosion. This requires rust-removing tools like sandpaper, a wire brush, and an angle grinder. Then, clean the surface to expose the bare, shiny metal. Then you can repair the once-rusty piece of metal by welding a new plate over the hole.
Which Type of Welder Should I Use When Welding Rusty Metals?
A stick welder is the preferred welding process method when welding rusty metal. You should use a 6010 or 6011 flux-coated welding rod and clean the rust from the work piece surface. The flux-cored wire creates an aggressive arc and deposits de-oxidizers in the weld puddle.
Can you use MIG welding for rusted metal? Of course, you can, if the metal corrosion is superficial and there is only basic surface rust. But you must clean all the rust and other contaminants from the surface. The best MIG wires to use are ER70S-6, ER70S-2, or ER70S-3.
Welding Rusty Metal — In Conclusion
It is possible to weld over rust if you clean the surface and use the proper equipment and the correct welding process. But it’s crucial to remember that there are limitations when welding rusty metal. And if you cannot remove all the rust, you should never use the piece in critical applications.
However, with patience and practice, you will be able to successfully learn the necessary skills to weld over rust.