Prep strategies to weld stainless steel

Using a Cleaning Routine to Eliminate Weld-Inhibiting Surface Residues

Table of Contents > 1. Impact of Surface Smut on The GMAW Process
2. The Intolerable Presence of GTAW Welding Contaminants
3. How To Clean Metal Before Welding
    3.1 Cleaning Prep Work On Aluminum Alloys
    3.2 Cleaning Prep Work On Ferrous Alloys
4. Stripping Away Galvanized Paint
5. Closing Thoughts on Welder Enacted Surface Cleaning
6. Using a Cleaning Routine to Eliminate Weld - FAQ

Let’s face it, even a seasoned welding professional can’t perform a strong, long-lasting joint if the surface of the workpiece is covered in rust or paint. Likewise, pro welders won’t achieve sought after work standards that will satisfy welding inspectors if the work is conducted on a contaminated metal, on a workpiece that’s buried under smut. That applies to galvanized paints and oxide coatings, too.

No matter the equipment, even if it’s one of our finest Tooliom machines, it won’t perform as it should if there’s an arc attenuating layer of muck in the way. To prove this statement, check out the effects of different material barriers on welding arcs.

Impact of Surface Smut on The GMAW Process

Typically a more forgiving technique, MIG welding arcs can only tolerate so much interference, as imposed by dirt or rust, paint or some oxide coating. Also known as GMAW, Gas Metal Arc Welding, the conductive circuit formed by the electrode and grounding clamp suffers due to poor conductivity. The arc wanders, the molten pool of metal fills with impurities, and the resulting weld lacks strength.

It gets worse, with spatter and flying debris endangering the welder’s safety. Paint and rust are both stubborn when exposed to arc energy, yet small quantities of their smutty materials will evaporate and enter the local area, only to be inhaled at some point in the process. Paint fumes are also loaded with toxic chemicals, any of which could cause health problems. Switching over to a workpiece covered in galvanized paint, the issue is exacerbated, with zinc particles leading to inhalation and the potential for “metal fume fever,” a condition that can lead to long-term health problems.
Dangers of Welding Fumes
Fusion completion defects, porosity headaches, lack of penetration and more, the problems form into a long list of bead weakening irregularities. Worst of all is this: all of these problems are avoidable if the welder stops to conduct a surface cleaning routine. And it doesn’t even take that long, not when done with the right tools.

The Intolerable Presence of GTAW Welding Contaminants

TIG welded joints, also known as Gas Tungsten Arc Welding, do not tolerate dirt or rust or paint. That’s one of the drawbacks of the process, but it’s one that’s more than made up for by the fact that TIG welds are applied with supreme precision. They cool as aesthetically pleasing joints, but that’s not possible if the weld zone is caked in smut.
Photo by @tig_welding_official(Ins)

Applied via a non-consumable tungsten electrode, the process is sensitive to surface contaminants. Again, the dirt and paint, rust or coatings vaporize to cause inhalation issues. Yet again, the materials become molten pool impurities, mixing with filler to undermine joint strength. Porosity in and around the bead is likely, as is cratering and brittle cracking.

Unique to tungsten welding, the electrode wears faster, requires more maintenance, and the expected clean, precise weld joint is marred by weld irregularities. Of course, the welder, one who isn’t conversant in cleaning techniques, might source a Tooliom TL-200M multi-process machine or some other high-efficiency model. They ramp up the arc to compensate for the wandering and poor conductivity issues, but that just creates more spatter. Even if the arc strengthens, the uncontrolled thermal load could deform the workpiece.

MIG/Stick/TIG Multi-Process Welder TL-200M 3 in 1 Welding Machine
MIG/Stick/TIG Multi-Process Welder TL-200M 3 in 1 Welding Machine|Tooliom

So far, then, joint compromising, health endangering workpiece smut is unacceptable in welding operations. As a worst case scenario, the hot flying debris engendered by work on a dirty part could cause a fire or chronic health issues. At best, the entire weld pool is polluted, so it’ll cool into a crack and porosity compromised joint that looks as ugly as it is weak. Preventative measures are simple - clean the workpiece first.
Porosity on TIG Weld
Porosity on TIG Weld

How To Clean Metal Before Welding

It all depends on the nature of the project. If the interfering smut is composed of dirt or paint, it’ll quickly become obvious to the welder what needs to be done. If the alloy is aluminum, then the film or coating attenuating the welding operation is less evident. Copper is another metal that tarnishes, by the way. It develops a coating, in the same way that aluminum does, that inhibits the formation of a welding arc. Coatings are insidious, forming on metals as thin films. They form when the metal is exposed to the atmosphere. Good storage practices can minimize this phenomenon, but there’s still likely to be some undesirable veneer.

Cleaning Prep Work On Aluminum Alloys

Leaving aside dirt and paint for the moment, the focus falls on aluminum. If the arc initiates, and that’s doubtful, it wanders and produces inclusions. The quality of the weld is substandard, and it only worsens when more energy is directed into the torch. Too much arc energy on aluminum ends up creating workpiece burnthrough. The job is ruined.

Instead of taking this road to ruin, an experienced welder pulls out a wire brush that’s reserved for the metal type. He gently scours away the dull coating. Afterwards, the alloy regains its metallic luster. The discolored, dull appearance is gone. If the workpiece is overly large, too big to clean with a small wire brush, there are other avenues available. Chemical solvents are one, with special alkaline solutions or alcohol based chemicals taking on the role of the solvent. The compounds dissolve the coating, leaving the surface metal in pristine condition. Last of all but every bit as effective, powered abrasive tools are applied with circular pads fitted. They spin at high speeds to abrade the film out of existence.

Metal Prep with Brush

Metal Prep with Brush

As for how to select the right approach to this issue, there’s no single answer to this question. Again, the areal coverage of the welding project matters, as does the thickness of the coating and its composition. For smaller projects, a simple wire brush is a viable option. On switching over to a large-scale job, abrasive tools are more practical. Beware if using chemicals, all due diligence must be taken when handling caustic chemical compounds.

Cleaning Prep Work On Ferrous Alloys

Before all else, don’t mix up wire brushes. If a tool has been used to clean an aluminum part, it’s never used for any other metal. Likewise, if a wire brush has been used to abrasively clean the site around a ferrous welding project, it can’t be applied to an aluminum job. To do so would be to invite disaster. Contaminating steel particles would pollute the joint and weaken it, leading to potential failure. It’s crucial to always keep separate brushes for different metals to ensure the integrity of the work. Additionally, cleaning prep work on ferrous alloys requires extra caution as these materials are prone to corrosion. Similar to aluminum, lightly use a dedicated wire brush or sandpaper to abrade the corrosion or dirt.

As ferrous alloys tend to accumulate tougher, grainier coatings of rust, a powered grinding tool will be required to scour off the worst of this contaminating layer. Just like how metal fabricators work with coarse then fine sandpaper grains, a switch to a fine-grained abrasive pad is recommended after the worst of the dirt and rust are gone. At this point, with the last traces of the surface irregularities cleaned away, the ferrous surface is restored to a smooth and semi-polished appearance.

Use a fine-grained abrasive pad to remove rust

Use a fine-grained abrasive pad to remove rust.

The chemical solvent path used specifically for ferrous surfaces takes on an even more rigorous aspect, with acids, dissolving gels and etching compounds coming to the fore. Stubborn deposits of rust often require the application of specialized corrosion removal agents, too. Again, when working with corrosive acids and solvents, pay attention to all safe chemical handling guidelines, please.


Use acid to remove rust.
Photo by @minute_of_dangle(TikTok)

Stripping Away Galvanized Paint

Designed to protect steel and other atmospherically reactive alloys from corrosion, zinc-based galvanized paints do a fine job of fulfilling their roles. However, what if the rust-protected metal needs to be welded? First of all, the job can’t be done as-is, not with zinc in the mix. The paint will cause undesirable defects. Worse still, it’ll evaporate and enter the atmosphere as a health endangering cloud of zinc particles.

Switch over to protective gloves and eye protection. Utilizing an angle grinder, the paint is scrubbed from the weld zone. Ideally, the zinc coating should be removed from an area that’s between 3 to 10 cm around the proposed joint. Chemical stripping can be used to gain the same results. Only, now there are two airborne hazards in play. Both the abraded, airborne zinc particles and the cloud of toxic chemical fumes are suspended in the atmosphere, ready to be inhaled. Mitigating this double-sided issue somewhat, ventilation and a respirator protect the welder from chronic health problems.

angle grinder removes paint

Angle grinder removes paint.

Treatment with muriatic acid removes thick layers of galvanized paint in a fraction of the time it would take using a powered tool, plus there are no airborne particulates to worry about when using chemicals. However, beware of getting this caustic solvent on exposed skin.

Closing Thoughts on Welder Enacted Surface Cleaning

Storage systems eliminate the need for most of these coatings scrubbing routines, at least that’s true if the welder is part of a team of metal fabricators working in the controlled environment of a factory. More than likely, however, welders will find themselves in hostile environments. The aluminum to be welded is already dull and filmed in aluminum oxide. Out in a boiler room or some other site that’s full of humidity, ferrous surfaces are caked in dirt and rust. A wipedown cloth removes the worst of the filth, then an angle grinder gets to work on the dirt and rust. Finally, an abrasive wheel removes the last of the rust. As can be observed here, the abrasive agents ramp downwards as each layer of the arc-subduing filth is scoured away, then the final layer is stripped off with a wire brush or sandpaper, thus respecting the surface integrity of the metal workpiece.

Every job is different. It’s part of a welder’s duties to evaluate the location of the job and adapt to that environment. If employed in a fabrication shop, much of this toiling is taken care of; the work metal is stored properly and locked away from contaminating elements. Even so, unless the storage area is a total vacuum, air will react with the metal. Aluminum oxide films will form. Expect a fabrication facility to have cleaning protocols in place. They’ll chemically remove the film or use angle grinders to prepare the job. The welder might even be able to sit out this phase of the job, waiting patiently for a fabrication technician to do the abrasive cleaning.



Out-on-the-job welders aren’t so lucky. They’re expected to do everything, although they may have a laborer accompanying them if the budget allows. Either way, job surfaces are going to experience a vast range of circumstantial factors. Some will be protected from rust, but that likely means galvanized paint is involved. Others will simply be rusty or covered in oils and regular paint. Of course, even regular paint can contain hazardous materials, this time in the form of lead. Again, don’t let lead into the air, use a chemical paint remover or a mask and ventilation. And know that, even without lead, binders and solvents in paint may cause inhalation irritation.

As part of their toolkit, wire brushes and angle grinders are kept light and mobile, ready to clean that metal and restore it to its lustrous best. Should a chemical solvent or something a little more caustic be needed, before firing up your Tooliom welding machine, remember to bring protective gloves, safety goggles and a respirator. The last piece of gear is for protection from that zinc-based paint.

TOOLIOM Tig Welding Gloves

TOOLIOM Tig Welding Gloves

Metal Surface Contaminant Cleaning Type Tools/Equipment Used
Rust Wire brush, abrasive tools, corrosion dissolving gels Angle grinders and wire brushes
Paint Wire brush, chemical strippers, abrasive tools Abrasive angle grinder (If not lead-based), otherwise, use a paint stripper chemical
Oxide Films Wire brush, chemical solvents, or abrasive tools Wire brush, mild alkaline solution, solvents, powered abrasive tools
Galvanized Paint Coatings Abrasive tools if small in scale and breathing apparatus or ventilation is on-hand Grinder, hammer & chisel, muriatic acid

Using a Cleaning Routine to Eliminate Weld-Inhibiting Surface Residues - FAQ

Q: What are some challenges that welding professionals face when working on a surface covered in rust or paint?

A: Welding on a surface covered in rust or paint poses challenges such as poor conductivity, interference with the welding arc, impurities in the molten metal pool, and weakened weld strength. Additionally, there are safety concerns related to spatter, flying debris, and inhalation of toxic fumes from paint or coatings.

Q: How does surface contamination affect Gas Metal Arc Welding (GMAW) or MIG welding?

A: In GMAW or MIG welding, surface contamination, such as dirt, rust, or paint, can lead to poor conductivity in the conductive circuit formed by the electrode and grounding clamp. This results in wandering arcs, impurities in the molten metal pool, and weakened welds. The presence of smutty materials can also contribute to health hazards when inhaled.

Q: Why is cleaning essential before Gas Tungsten Arc Welding (GTAW) or TIG welding?

A: TIG welding is sensitive to surface contaminants, and the presence of dirt, rust, or paint can lead to welding defects such as porosity, cratering, and brittle cracking. Tungsten electrodes wear faster, and the precision of TIG welds is compromised. Cleaning is crucial to maintaining the high precision and quality associated with TIG welding.

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