Stick welding porosity usually comes from gas trapped in the weld metal before the puddle freezes. With SMAW, start with the electrode, base metal, arc length, amperage, polarity, and technique before blaming the welder. Pinholes after slag removal, wormholes in the bead, rough starts, popping arc behavior, and scattered pits usually point to moisture, contamination, long arc length, wrong rod handling, or welding over paint, oil, rust, zinc, primer, or damp steel.
The repair path is simple: stop welding, identify whether the porosity is surface-only or through the bead, clean the joint to bright metal, switch to known-good electrodes, shorten the arc, verify amperage and polarity, and run a controlled test bead on clean scrap. For low-hydrogen rods, especially 7018, porosity must be treated as a storage and hydrogen-control issue, not only a bead appearance problem. See the related WSP guide on 7018 rod moisture contamination when damp rods, sticking, or cracking risk are present.
Common Symptoms
| Symptom | Likely Cause | First Check |
|---|---|---|
| Small pinholes after chipping slag | Moisture, contamination, or long arc | Try dry rods on clean scrap |
| Wormholes or tunnels in bead | Severe contamination or trapped gas | Grind out and clean joint |
| Porosity starts after rod change | Bad rod batch, damp coating, wrong rod storage | Compare against sealed rods |
| Porosity only at starts | Poor restart, long arc, damp rod tip | Clip/restrike properly and shorten arc |
| Porosity on rusty or painted steel | Surface contamination burning into puddle | Remove coating and re-test |
| Porosity with 7018 plus sticking | Low amperage, damp coating, bad arc length | Check storage and amperage |
Likely Causes
Moisture in electrodes: Damp coating can release hydrogen and other gases into the weld pool. Low-hydrogen electrodes are especially sensitive. Opened 7018 should be stored according to the electrode manufacturer, code, and WPS requirements.
Dirty base metal: Oil, grease, paint, primer, rust, mill scale, cutting fluid, galvanized coating, and moisture can create gas pockets when heated. Stick welding is more tolerant than TIG or MIG, but it is not immune to contamination.
Long arc length: A long arc can reduce shielding from the electrode coating and pull air into the arc zone. This is common with new operators trying to see the puddle.
Wrong rod manipulation: Excessive whipping with low-hydrogen rods can cause porosity. Some cellulose rods tolerate whip-and-pause technique, but 7018 should normally be run with a short, steady arc.
Wrong amperage or polarity: Too-low amperage can leave a cold, sluggish puddle that traps gas. Wrong polarity can create instability, spatter, poor penetration, and porous starts. If the symptom includes sticking, review 7018 rod sticking causes and solutions.
Quick Checks
- Use fresh, known-good electrodes from sealed or properly stored packaging.
- Clean the weld area to bright metal at least 1/2 in beyond the weld zone.
- Remove oil, paint, primer, zinc, moisture, rust, and grinding dust before welding.
- Shorten the arc until the puddle is controlled and the arc sounds steady.
- Verify polarity: 6010 commonly requires DCEP, while many 7018 rods run on AC or DCEP depending on formulation.
- Check amperage against the rod diameter, position, and manufacturer chart.
- Run one test bead on clean scrap with one change at a time.
Root Cause Analysis
If porosity disappears on clean scrap with fresh rods, the welder is probably not the root cause. The problem is usually the workpiece surface, electrode condition, or joint environment. If porosity follows one rod container but not another, quarantine the suspect rods. If porosity appears only in vertical or overhead work, look at arc length, travel speed, rod angle, and slag control.
For rod selection, the difference between cellulose and low-hydrogen electrodes matters. WSP’s 6010 vs 7018 guide explains that 6010 is used for digging penetration and root work, while 7018 is used for low-hydrogen structural welds. Do not store or run them the same way. Mixing 6010 and 7018 in the same oven or job box can create wrong-rod and wrong-storage problems.
Inspection Steps
- Chip and wire-brush the weld. Confirm whether holes are isolated surface pits or continuous porosity.
- Grind one defect open. If holes continue below the surface, remove the weld until sound metal is reached.
- Inspect rod coating. Reject rods with cracked, swollen, oily, soft, rusty, chipped, or wet coating.
- Check base metal. Look for paint, oil, water, galvanizing, primer, heavy rust, cutting fluid, and laminations.
- Check machine setup. Confirm amperage, polarity, lead connections, work clamp contact, and cable condition.
- Check technique. Look for long arc, excessive weave, whipping with low-hydrogen rods, or travel speed too fast for gas escape.
- Make a comparison weld using clean scrap and fresh rods. If the test is sound, return to the workpiece and correct cleaning or joint conditions.
Test Procedures
Use a clean scrap coupon of the same material when possible. Run three beads: one with the suspect rod, one with a fresh rod from sealed storage, and one after changing arc length and amperage. Keep polarity, rod diameter, and base metal consistent. If only the suspect rod creates porosity, remove that rod batch from critical work. If all beads are porous, inspect work clamp contact, machine output, arc length, and surface preparation.
For 7018, test beads are not proof of low-hydrogen compliance. A rod can make an acceptable-looking bead and still be unacceptable for code, pressure, structural, lifting, or restrained work if exposure history is unknown. Follow the WPS, inspector, electrode manufacturer, or engineer requirement.
Visual Wear Indicators
- Electrode coating cracks: moisture cycling, impact damage, or old stock.
- Soft or powdery coating: moisture damage; do not use for critical welds.
- Rust on exposed core wire: storage failure or aged rods.
- Oily rod surface: contamination that can create porosity and fumes.
- Blackened start pits: poor restart, contamination, or arc instability.
- Glassy irregular slag on 7018: possible damp coating or incorrect settings.
Compatibility Notes
Verify electrode classification, rod diameter, polarity, amperage range, base metal, position, and storage requirement before ordering or welding. E6010, E6011, E7014, E7018, E7018-1, E7018AC, stainless electrodes, nickel cast-iron rods, and hardfacing electrodes do not share the same storage, polarity, or technique rules. When the rod is unknown, label it Unknown (Verify) and do not use it on critical welds.
What To Verify Before Ordering
- Exact electrode class and brand required by the WPS or repair procedure.
- Rod diameter that matches material thickness, position, and available amperage.
- Machine output and polarity compatibility.
- Whether 7018AC is required for an AC-only transformer machine.
- Whether low-hydrogen storage, sealed cans, rod oven, or quiver control is required.
- Base metal condition: clean mild steel, rusty repair work, galvanized, coated, cast iron, hardfacing, or unknown alloy.
Common Wrong-Part Mistakes
- Using old open 7018 from a toolbox on a structural repair.
- Buying standard 7018 for a machine that only runs AC poorly.
- Using 6010 because it burns through contamination instead of cleaning the joint.
- Running a specialty electrode like nickel or hardfacing without checking polarity and procedure.
- Assuming porosity is always caused by amperage when the rod is damp or the base metal is contaminated.
Field Fix vs Proper Fix
| Condition | Field Fix | Proper Fix |
|---|---|---|
| Pinholes with 7018 | Try fresh dry rods on clean scrap | Correct rod storage and follow WPS exposure limits |
| Porosity over paint or rust | Grind test area clean | Remove coating from full weld zone before welding |
| Long arc porosity | Shorten arc and reduce travel speed | Retrain technique and verify settings |
| Damp rods in the field | Use sealed fresh rods for noncritical testing | Use approved oven/quiver procedure or discard |
| Wormholes in finished weld | Stop and mark defect | Grind out to sound metal and reweld under corrected conditions |
Related Failure Paths
Porosity often travels with rod sticking, slag inclusions, lack of fusion, undercut, arc blow, cracking, and failed visual inspection. A bad ground or unstable arc can make the operator hold a longer arc, which then creates porosity. Damp 7018 can create porosity and increase hydrogen-cracking risk. Poor fume control is also common when welding dirty, coated, or contaminated steel; review welding fume extractor troubleshooting when smoke is not being captured at the arc.
Safety Notes
Do not weld over unknown coatings, paint, solvent residue, oil, galvanized coating, plating, or contaminated steel without identifying the hazard. Use ventilation, fume extraction, correct helmet shade, dry gloves, fire watch, and electrical safety practices. Keep your head out of the plume. Do not use wet rods, improvised rod heating, torch-baked electrodes, microwave drying, or truck-dash drying for low-hydrogen work.
Sources Checked
- Washington Alloy electrode catalog sections on 6010, 7018, low-hydrogen welding tips, and porosity warnings related to whipping low-hydrogen electrodes.
- Lincoln Electric consumables storage and handling guidance for covered electrodes and moisture-resistant packaging.
- Weld Support Parts stick welding support articles on 7018 moisture contamination, 7018 sticking, 6010 vs 7018 selection, and fume extraction troubleshooting.
