Flux-cored arc welding splits into two distinct processes: self-shielded (FCAW-S) and gas-shielded (FCAW-G, also called dual-shield). Self-shielded wire generates all its shielding from flux compounds inside the wire and needs no gas bottle. Gas-shielded wire uses an external gas supply, typically 100% CO2 or 75/25 argon/CO2, in addition to its flux core. Choosing the right one depends on where you’re welding, what code requirements you’re under, and how much cleanup time you can tolerate.
FCAW-S dominates outdoor structural work and field welding. FCAW-G owns the shop fabrication world where gas protection isn’t disrupted by wind. The two processes use different polarity, different wire formulations, and produce noticeably different weld characteristics.
How Self-Shielded FCAW Works
Self-shielded flux-cored wire (FCAW-S) carries all its shielding agents, deoxidizers, and slag-forming compounds inside a tubular wire electrode. When the arc melts the wire, these flux compounds decompose. Some form a slag that covers the weld pool. Others vaporize into gases that displace atmospheric oxygen and nitrogen from the arc zone.
Common self-shielded wires include:
- E71T-11 (Lincoln Innershield NR-211-MP): All-position, general-purpose, DCEN polarity. The most popular self-shielded wire for small shops and field work. 0.030", 0.035", and 0.045" diameters.
- E71T-GS: All-position, single-pass only, DCEN. Found in most retail welding wire packages. Adequate for hobby use and light fabrication but not rated for multi-pass structural work.
- E71T-8 (Lincoln Innershield NR-232): Low-hydrogen, all-position, DCEN. Meets AWS D1.8 seismic requirements. Used for structural steel connections in earthquake zones.
Self-shielded wire runs on DCEN (electrode negative) polarity. This is the opposite of solid MIG wire and gas-shielded flux-core, which run DCEP. Getting the polarity wrong produces terrible welds with excessive spatter and porosity.
Characteristics of Self-Shielded Welds
Self-shielded FCAW produces more smoke and fume than any other common arc welding process. The arc is louder. Spatter production is higher. The slag coating is thicker and harder to remove. Weld appearance is rougher compared to gas-shielded or solid MIG wire.
Despite the cosmetic downsides, FCAW-S penetrates well on heavy steel and tolerates surface contamination like mill scale, light rust, and primers better than solid wire. Deposition rates of 4-10 lbs/hour are typical with 0.045" wire in all positions.
How Gas-Shielded FCAW Works
Gas-shielded flux-cored wire (FCAW-G) uses external shielding gas to protect the arc zone while the internal flux provides additional shielding, slag, and deoxidizers. The gas does most of the atmospheric protection work, so the flux formulation can focus on metallurgical properties and slag characteristics.
Common gas-shielded wires include:
- E71T-1 (Lincoln Outershield 71M, ESAB Dual Shield 7100 Ultra): All-position, DCEP polarity, 75/25 or CO2. The workhorse wire for structural fabrication shops. Available in 0.035", 0.045", 1/16", and 5/64" diameters.
- E70T-1: Flat and horizontal only, DCEP, 75/25 or CO2. Higher deposition rates than E71T-1 since it doesn’t need the fast-freeze slag for out-of-position work.
- E81T1-Ni1: 1% nickel for improved low-temperature toughness. Used where Charpy impact requirements go below -20F (-29C).
Gas-shielded wire runs on DCEP (electrode positive) polarity, just like solid MIG wire. Shielding gas is either 100% CO2 or 75% argon / 25% CO2. Pure CO2 gives deeper penetration but more spatter. The 75/25 mix produces a smoother arc with less spatter and better bead appearance.
Characteristics of Gas-Shielded Welds
Gas-shielded FCAW produces a smoother, more stable arc than self-shielded. Spatter is moderate, roughly between solid MIG wire and self-shielded flux-core. The slag is thinner and easier to remove. Weld appearance is significantly cleaner. Fume and smoke levels are roughly half of self-shielded wire.
Deposition rates with gas-shielded wire are impressive. With 1/16" E71T-1 wire in flat position, rates of 12-20 lbs/hour are common. That’s 2-3 times what solid MIG wire deposits at the same amperage.
Head-to-Head Comparison
| Factor | Self-Shielded (FCAW-S) | Gas-Shielded (FCAW-G) |
|---|---|---|
| Shielding Gas | None required | 75/25 or 100% CO2 |
| Polarity | DCEN | DCEP |
| Common Wires | E71T-11, E71T-GS, E71T-8 | E71T-1, E70T-1, E81T1-Ni1 |
| Wind Tolerance | Excellent, 30+ mph | Poor, similar to MIG |
| Smoke/Fume | Very high | Moderate |
| Spatter | High | Moderate |
| Weld Appearance | Rougher, heavy slag | Smoother, lighter slag |
| Deposition Rate (0.045") | 4-10 lbs/hr | 8-14 lbs/hr |
| Penetration Profile | Broad, shallow | Deeper, finger-type with CO2 |
| Typical Applications | Field, outdoor, structural erection | Shop fabrication, heavy plate, structural |
| Equipment Cost | Lower (no gas system needed) | Higher (gas bottle, regulator, hose) |
| Operating Cost per lb | Wire costs more per lb | Wire cheaper, but gas adds cost |
Penetration Differences
The penetration profile differs significantly between the two processes. Self-shielded FCAW on DCEN produces a broader, shallower penetration pattern. The heat spreads across a wider area rather than digging deep. This works well for general fabrication joints where you want good fusion without excessive dig.
Gas-shielded FCAW on DCEP with CO2 gas produces a narrower, deeper penetration profile, sometimes called “finger penetration.” The concentrated arc digs into the root of the joint. This is an advantage on heavy plate and multi-pass groove welds where deep root fusion matters. With 75/25 gas, the penetration is still deeper than self-shielded but slightly less aggressive than pure CO2.
For thick steel (3/4" and up), gas-shielded FCAW for heavy plate is the standard approach in most fabrication shops.
When to Use Self-Shielded
Self-shielded FCAW is the right choice in these situations:
Outdoor and field welding. Wind kills MIG and gas-shielded flux-core by blowing away the shielding gas. Self-shielded wire doesn’t care about wind because it generates its own protection. Construction ironworkers, pipeline welders, and structural erectors run self-shielded FCAW almost exclusively outdoors. See flux-core outdoor welding for technique specifics.
Remote locations without gas supply. If you’re welding on a ranch, in a mine, or at a remote construction site where gas bottle delivery isn’t practical, self-shielded wire is the answer.
Portable MIG welders. Small 110V and 230V MIG machines often ship with a spool of E71T-GS self-shielded wire. For hobbyists and occasional welders, running self-shielded flux-core means no gas bottle expense and simpler setup.
Code-required low-hydrogen in the field. E71T-8 self-shielded wire meets AWS D1.8 seismic welding requirements. When the code demands low-hydrogen deposits in the field where gas-shielded welding isn’t practical, E71T-8 fills the gap.
When to Use Gas-Shielded
Gas-shielded FCAW is the right choice in these situations:
Shop fabrication on heavy steel. The higher deposition rates, cleaner welds, and better mechanical properties make dual-shield the default process for structural steel fabrication shops. Multi-pass groove welds on 1/2" to 2" plate are where this process really shines. For more on this, see dual-shield welding explained.
Structural welding to AWS D1.1. Gas-shielded E71T-1 and E71T-1M are pre-qualified under AWS D1.1, making procedure qualification straightforward. Many structural fabricators standardize on E71T-1 with 75/25 gas.
High-production environments. The deposition rate advantage of dual-shield, especially with 1/16" and 5/64" wire diameters, translates directly into reduced labor hours on large fabrication projects.
Better weld quality requirements. When the job calls for cleaner welds with less cleanup, less spatter, and better mechanical properties (especially at low temperatures), gas-shielded wire is the clear choice.
Polarity: The Critical Setup Difference
Getting the polarity wrong is the most common FCAW mistake, and it produces terrible results. The rule is simple:
- Self-shielded (FCAW-S): DCEN (electrode negative, wire connects to negative terminal)
- Gas-shielded (FCAW-G): DCEP (electrode positive, wire connects to positive terminal)
On many MIG/flux-core machines, switching polarity requires swapping the cable connections inside the machine. Some machines have an external polarity switch. Check your machine’s manual for the procedure.
Running self-shielded wire on DCEP causes excessive spatter, porosity, and poor penetration. Running gas-shielded wire on DCEN causes an unstable arc, excessive spatter, and weld defects. If your welds suddenly look terrible with a new spool of wire, polarity is the first thing to check.
Drive Roll and Feeding Considerations
Flux-cored wire is softer than solid wire because of the tubular construction. Crushing the wire with the drive rolls compresses the flux core and causes feeding problems.
For self-shielded wire: Use knurled (V-knurl) drive rolls. Set tension just enough to feed reliably without crushing the wire. If you see the wire flattening at the drive rolls, reduce tension.
For gas-shielded wire: Use V-knurl drive rolls for small diameters (0.035" and 0.045"). For larger diameters (1/16" and up), some manufacturers recommend standard V-groove rolls. Follow the wire manufacturer’s drive roll recommendation.
In both cases, keep the gun liner and contact tip sized for flux-core wire. A liner that’s too tight restricts the softer wire. A contact tip that’s too large causes arc wander. For guidance on managing the other major annoyance of FCAW, see spatter reduction techniques.
Stick-Out (CTWD) Differences
Contact-tip-to-work distance (CTWD), commonly called stick-out, differs between the two processes:
- Self-shielded: 3/4" to 1-1/4" (19-32mm) is typical. Longer stick-out increases resistance heating of the wire, which affects deposition rate and penetration.
- Gas-shielded: 3/4" to 1" (19-25mm) is typical. Shorter than self-shielded because the gas nozzle needs to be close enough to the arc for effective shielding.
Consistent stick-out is critical for both processes. Changing stick-out changes the amperage. A 1/4" increase in stick-out can drop amperage by 20-25 amps. For detailed settings by wire diameter, see flux-core welding settings.
Smoke and Ventilation Requirements
Self-shielded FCAW produces more welding fume than any other common arc process. The volume of fume can be 3-5 times what MIG welding produces and roughly double what gas-shielded flux-core generates. This is a real occupational health concern.
In a shop setting with self-shielded wire, you need aggressive ventilation: fume extractors at the source, overhead hoods, or a supplied-air respirator. Outdoor welding dissipates the fume naturally, which is one reason self-shielded wire and outdoor work pair well.
Gas-shielded FCAW generates less fume, but still more than solid MIG wire. Standard shop ventilation (source capture or general dilution) handles gas-shielded fume in most situations.
Cost Comparison
Self-shielded wire costs more per pound than gas-shielded wire. A 10 lb spool of E71T-11 in 0.045" runs about $35-50, while E71T-1 gas-shielded in the same diameter costs $25-40 per 10 lb spool (prices at time of writing). However, self-shielded welding has no gas cost.
A 300 CF cylinder of 75/25 shielding gas costs $30-50 to refill and lasts roughly 8-12 hours of actual arc time at 35-45 CFH flow rate. A CO2 cylinder costs less to fill but the flow rate is similar.
For occasional welding, self-shielded wire saves money because there’s no gas expense or cylinder rental. For production work, gas-shielded wire’s higher deposition rate and less cleanup time make it cheaper per foot of weld.
Common Problems and Fixes
Porosity with self-shielded wire: Usually caused by excessive stick-out, wrong polarity, or welding over heavy oil or paint. Clean the base metal, verify DCEN polarity, and keep stick-out at 3/4" to 1".
Worm tracking (herringbone lines in the weld): Gas entrapment in the slag caused by painting over hot slag or welding over contamination. Clean the joint and let each pass cool enough for slag removal before the next pass.
Excessive spatter with gas-shielded wire: Check polarity (must be DCEP). Verify gas flow at 35-45 CFH. Voltage may be too low for the wire feed speed. See flux-core wire selection for correct parameter ranges.
Incomplete slag removal: Self-shielded slag is harder to remove than gas-shielded. Some wires produce self-peeling slag, others need aggressive chipping. If slag stubbornly adheres, your heat input may be too low. Increase voltage or slow your travel speed slightly to let the weld pool wet out fully before the slag solidifies.