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What ER70S-6 Can—and Cannot—Do
ER70S-6 is a common solid MIG wire for mild and low-alloy steel. Its higher levels of manganese and silicon help it deoxidize the weld pool, so it can handle light surface rust or mill scale better than lower-deoxidizer wire such as ER70S-3. That makes it a sensible default for repair work on steel that is clean in spots but not perfectly prepared.
“Better on dirty steel” does not mean “weld through anything.” Heavy rust, thick scale, paint, oil, and galvanizing can still cause porosity, inclusions, poor fusion, or hazardous fumes. Remove loose scale and contamination before welding. ER70S-6 is a forgiving wire, not a substitute for preparation.
Which Wire to Buy
For most home and shop work, buy ER70S-6 in the diameter that suits your welder and material. A 0.030-inch spool is a versatile choice for sheet and general fabrication; 0.035-inch wire can be more comfortable on thicker stock and higher-output machines. Check your machine’s drive rolls, contact tip, and recommended wire range before ordering. A small 2-pound spool is practical for occasional repairs, while a 10- or 11-pound spool usually costs less per pound if you weld regularly.
For a general-purpose spool, compare 0.030-inch ER70S-6 MIG wire with the wire diameter your machine is set up to feed. If you routinely weld heavier material, look at 0.035-inch ER70S-6 MIG wire. Brand matters less than correct classification, a sealed spool, and consistent feeding; an unknown spool with poor packaging or uneven winding can cause more trouble than a modest price difference.
Wire and Process Comparison
| Option | Best fit | Trade-off on rusty or scaled steel |
|---|---|---|
| ER70S-6 solid wire, shielding gas | Indoor shop work and clean-to-lightly-scaled steel | Good deoxidizing action and low spatter when set up well; wind or poor gas coverage can cause porosity. |
| ER70S-3 solid wire, shielding gas | Clean steel and controlled fabrication | Often fine and sometimes cheaper, but less tolerant of surface oxidation than ER70S-6. |
| Gasless flux-core wire | Outdoor work or places where shielding gas is impractical | Handles drafts better, but produces slag and more cleanup; use the correct wire polarity and settings. |
Solid ER70S-6 usually runs with a mixed shielding gas such as 75% argon/25% carbon dioxide, or with carbon dioxide where appropriate. Use the gas specified for the wire and machine. Gasless flux-core wire is not ER70S-6 solid wire: it is a different consumable with different polarity, setup, and weld cleanup requirements.
Prepare the Steel and Set the Machine
Brush or grind away loose rust and scale, then remove oil, paint, and other coatings from the joint area. For a butt joint, clean both sides where accessible; contamination on the back can still affect the weld. A practical starting point is bare metal for roughly 1/2 inch (12 mm) on either side of the seam, expanding that area if the coating or scale continues. On galvanized steel, remove the coating from the weld zone and provide strong ventilation; zinc fumes are hazardous.
Use the machine’s wire-feed and voltage chart as a starting point, not a guarantee. Voltage, feed speed, wire diameter, joint fit-up, and material thickness all interact. Make a test weld on matching scrap, then check for steady feeding, an even bead, and fusion at the toes. On thin sheet, too much heat can burn through; on thicker steel, low heat or poor travel technique can leave a bead sitting on top without proper fusion.
Keep shielding gas flow near the range recommended for your setup—often about 20–30 cubic feet per hour indoors, though nozzle size and drafts change what works. Excessive flow can create turbulence and draw air into the shield. If a porous bead appears, check for gas leaks, a blocked nozzle, drafts, dirty base metal, and worn consumables before assuming the wire is defective.
Common Problems and Trade-offs
ER70S-6 can leave a thin silicon-rich film or small glassy islands on the bead. This is normal for many solid-wire welds, but it can interfere with a second pass or paint adhesion; brush or grind the surface before coating or welding over it. More spatter may point to poor settings, an excessive stickout, dirty steel, or unstable gas coverage rather than a need to buy a more expensive spool.
For lightly rusty material, ER70S-6 is often worth the small premium over ER70S-3. For clean, well-prepared steel, the cheaper ER70S-3 can be perfectly adequate. For heavy scale or rust, neither wire eliminates the need to clean: welding over thick contamination risks a weak joint even when the surface bead looks acceptable. If the work is structural, safety-critical, or governed by a welding procedure, follow the specified consumable and preparation requirements instead of choosing wire by convenience.