Understanding Stick Welding

Shielded Metal Arc Welding (SMAW), commonly known as stick welding, is one of the most widely used arc welding processes for repair and maintenance work. It relies on a consumable electrode coated with flux that decomposes during the arc to form a protective gas shield and a slag covering over the molten weld pool. The process is simple, portable, and highly effective for outdoor and field repairs where wind might disrupt gas shielding processes like MIG or TIG. Stick welding works exceptionally well on rusty or painted surfaces if properly prepared, and it can be used on a wide range of ferrous and some non-ferrous metals.

The electric arc generated between the electrode tip and the base metal reaches temperatures exceeding 5,000°F (2,760°C), melting both the electrode core wire and the base material. As the flux coating burns, it releases shielding gases that protect the molten weld from atmospheric oxygen and nitrogen, which would otherwise cause porosity and embrittlement. The slag formed from the flux settles on top of the finished weld bead and must be chipped off after cooling. This slag layer also slows the cooling rate, reducing the risk of cracking in hardenable steels.

Common Defects in Metal Structures

Before diving into repair techniques, it’s important to understand the types of cracks and defects you’re likely to encounter. Cracks in metal structures generally fall into two broad categories: hot cracks and cold cracks. Hot cracks occur at elevated temperatures during solidification or immediately after welding, while cold cracks develop at lower temperatures, often hours or days after welding, due to hydrogen embrittlement or residual stress. Other common defects include:

  • Fatigue cracks – Caused by cyclic loading, often starting at stress concentrators like sharp corners or weld toes.
  • Stress corrosion cracks – Result from combined tensile stress and a corrosive environment.
  • Porosity – Gas pockets trapped in the weld metal, weakening the joint.
  • Slag inclusions – Non-metallic particles trapped between weld layers.
  • Undercut – A groove melted into the base metal at the weld toe, reducing cross-sectional area.

Identifying the root cause of a defect is critical. For example, fatigue cracks often require removal of the crack tip beyond visible length, while stress corrosion cracks may demand a different filler metal or post-weld heat treatment to prevent recurrence.

Preparations for Stick Weld Repair

Thorough preparation is the single most important factor in achieving a durable stick weld repair. The original article outlines basic cleaning steps, but here we expand with industry best practices.

Surface Cleaning and Defect Removal

All contaminants—rust, paint, oil, grease, mill scale, and moisture—must be removed at least 1 to 2 inches around the defect. Use a wire brush, angle grinder with abrasive wheels, or a needle scaler for heavy rust. For oil or grease, wipe with a solvent like acetone or denatured alcohol and allow to dry completely. Moisture in the joint can introduce hydrogen, leading to cold cracking. If the base metal is wet, preheat to drive off moisture.

Defect Excavation and Groove Preparation

Cracks must be completely removed before welding. Use a thin grinding wheel (¼ inch or less) to create a narrow groove that follows the crack. A “U” or “V” groove shape is typical, with a root opening of about 1/8 to 3/16 inch for access. Techniques like drilling stop holes at both ends of the crack can prevent propagation during preparation. The hole diameter should be roughly 1/8 to ¼ inch. After drilling, grind out the crack from one stop hole to the other, ensuring all discolored metal is gone. Use dye penetrant or magnetic particle testing to confirm complete removal.

Preheating and Interpass Temperature Control

For carbon steel above 3/4 inch thickness, high-strength steels, or cast iron, preheating is essential to reduce cooling rates and minimize cracking. The preheat temperature depends on the carbon equivalent and material thickness; common ranges are 200°F to 600°F (95°C to 315°C). Use a temperature-indicating crayon, infrared thermometer, or thermocouple to monitor. Maintain the interpass temperature (the temperature between weld passes) within 50°F of the preheat value. This ensures consistent weld metal properties and reduces hydrogen cracking risk.

Selecting the Right Electrode

Electrode selection dramatically affects the success of a stick weld repair. The American Welding Society (AWS) classifies electrodes with a four- or five-digit number. For example, E7018 means a 70,000 psi tensile strength, all-position electrode with a low-hydrogen potassium coating. Low-hydrogen electrodes (E7016, E7018, E8018) are strongly recommended for repair of high-strength steels and when there is a risk of hydrogen cracking. For thin materials or vertical-up welding, E6010 (cellulose sodium) offers deep penetration and a fast-freezing slag, ideal for root passes and pipe welding. E6013 is a general-purpose electrode for sheet metal and easy-to-weld filler passes. E308/309 stainless electrodes are used for repairing stainless steel components, while ENi-CI nickel electrodes are specifically formulated for cast iron repairs. Always match the filler metal tensile strength to the base metal or use a lower-strength overmatch when the base metal’s exact grade is unknown.

Performing the Stick Weld Repair

With the work prepared and the appropriate electrode in hand, proper technique is the next critical step. The original article lists five steps, but a deeper technique explanation can greatly improve results.

Machine Settings and Arc Length

Set the amperage according to the electrode diameter and manufacturer’s recommendations. For a ⅛-inch (3.2 mm) E7018, the typical range is 90–130 amps, while a 5/32-inch (4.0 mm) E7018 uses 120–175 amps. Use DC reverse polarity (electrode positive) for E7018 and AC for many general-purpose electrodes. Maintain a short arc length—about equal to the core wire diameter—to prevent spatter and slag entrapment. A long arc increases heat input and can cause undercut and porosity.

Travel Speed and Manipulation

Travel speed must be steady and appropriate for the weld size. If you move too fast, the weld bead will be narrow and convex, with poor fusion to the side walls. Too slow creates a wide, flat bead with excessive slag coverage and potential slag inclusions. For filling a groove completely, use a stringer bead (straight travel) for root passes and shallow grooves. For wider gaps, a weave bead (oscillating motion) can cover more area per pass. A common weave pattern is a slight back-and-forth motion with a pause at the edges to ensure sidewall fusion. Keep the weave width no more than 2½ times the electrode diameter to maintain control.

Multiple Pass Technique

For deep cracks or thick sections, do not attempt to fill the entire groove in one pass. That would risk excessive heat input, distortion, and lack of fusion. Instead, use multiple passes, allowing each to cool below the interpass temperature if required. The root pass should penetrate fully into the groove bottom. Subsequent fill passes are deposited with a slight overlap of the previous bead. The final cap pass should be slightly convex and well-fused to the base metal edges. After each pass, chip off the slag and clean between passes with a wire brush.

Peening

Peening—the process of striking the weld metal with a blunt tool (e.g., a ball-peen hammer) while it is still hot—can help relieve tensile stresses and reduce the risk of cracking in high-restraint joints. Use moderate blows and avoid peening the root pass or the cap pass. Peening is most effective on intermediate fill passes. Always check the base metal type; too much peening on hardenable steels can cause work hardening and microcracking.

Post-Weld Inspection and Finishing

After completing the weld, immediate visual inspection is essential. Look for surface cracks, slag spots, excessive spatter, and undercut. Allow the weld to cool to room temperature, then perform non-destructive testing (NDT) as required by the application’s safety standards. Common NDT methods include:

  • Visual inspection (VT) – Check for surface discontinuities; use a magnifying glass for small cracks.
  • Dye penetrant testing (PT) – Apply a red dye then a developer; cracks show as bright red lines.
  • Magnetic particle testing (MT) – For ferromagnetic materials; cracks reveal themselves as lines of particles under magnetic field.
  • Ultrasonic testing (UT) – For subsurface defects; requires a trained operator.

If the repair is approved, finish the surface by grinding any reinforcement (cap) flush if a smooth surface is required, but avoid grinding into the base metal. For stress-sensitive joints, post-weld heat treatment (PWHT) may be necessary to relieve residual stresses and temper hardened zones. Typical PWHT temperatures for carbon steel range from 1,100°F to 1,250°F (595°C to 675°C), held for one hour per inch of thickness, then slow-cooled.

Troubleshooting Common Issues

Even experienced welders encounter problems. Below is a quick reference for common stick welding defects in repair work.

Porosity

If the weld bead has a spongy appearance or gas pockets, the cause is usually inadequate shielding. Check for strong air drafts, wet electrodes, or a dirty base metal. Use low-hydrogen electrodes (E7018) stored in a rod oven at 250°F–300°F (120°C–150°C) and limit exposure to air. Avoid dragging the electrode through moisture. If porosity persists, increase the arc length slightly to ensure gas coverage.

Slag Inclusions

Trapped slag in the weld metal often results from poor cleaning between passes or wrong manipulation. Make sure slag from the previous pass is completely removed with a chipping hammer and wire brush. Use a 45° drag angle and slightly shorter arc to push slag to the rear. A weaving motion may trap slag at the toes; stick to stringer beads if slag inclusions are frequent.

Undercut

Undercut is a groove melted into the base metal at the weld toe. It reduces the effective thickness and can initiate fatigue cracks. Undercut is caused by excessive heat input, too high a travel speed, or weaving too wide. Reduce amperage by 10–15%, travel a little slower, and pause at the edges during a weave to allow filler metal to fill the toe. If undercut appears, grind it out and deposit a smooth wash pass.

Cold Cracking (Hydrogen Cracking)

Cold cracks appear hours after welding, often in the heat-affected zone. Prevention requires a three-pronged approach: use low-hydrogen electrodes, preheat the joint sufficiently, and ensure slow cooling (or post-weld heating). Using a baking oven for electrodes (stored at 250°F for at least 2 hours before use) is critical. Also, avoid quenching the weld with water.

Safety Considerations

The original article notes basic PPE and ventilation. We expand here with additional safety details specific to stick welding repair.

Arc Radiation and Personal Protective Equipment

The welding arc emits intense ultraviolet (UV) and infrared (IR) radiation that can cause severe burns to the skin and permanent eye damage (arc eye). Always wear an auto-darkening welding helmet with a shade rating of 10–13 (11–12 for stick welding is typical). Protect all exposed skin with flame-resistant leather gauntlet gloves, a welding jacket or leather apron, and a dark-colored cotton shirt. For overhead welding, wear a beanie cap and ear plugs to protect from sparks.

Fume Management

Stick welding produces fumes containing metal oxides, fluorides, and other compounds. Long-term exposure can cause serious lung conditions. The American Welding Society (AWS) and OSHA recommend local exhaust ventilation (LEV) or a respirator when welding in confined spaces or when ventilation is poor. A half-mask respirator with P100 filters is a minimum for general fume protection. Avoid welding on coated metals (e.g., galvanized or painted) without extreme ventilation—zinc oxide fumes cause metal fume fever, an acute illness resembling influenza.

Electrical Safety

Stick welding uses high current (50–350 amps) at relatively low voltage (20–40 volts). The open-circuit voltage (OCV) can be 70–100 volts, enough to cause a dangerous shock, especially in wet conditions. Always use dry, insulated gloves. Keep the work clamp firmly attached to clean base metal, and never touch the electrode or electrode holder with ungloved hands while the machine is on. Inspect cables for frayed insulation. For outdoor work, use a ground fault circuit interrupter (GFCI) outlet if plugging into a portable generator or mains power.

Fire and Explosion Prevention

The welding arc can reach over 5,000°F, so it can easily ignite flammable materials. Clear the area of combustibles at least 35 feet from the work point. Keep a fire extinguisher rated for Class ABC fires within easy reach. Never weld on sealed containers or drums without proper venting—heat can vaporize residual contents and cause an explosion. For repair welding on tanks, pipes, or fuel systems, follow the National Fire Protection Association (NFPA) 51B standard.

Conclusion

Stick welding, when executed with careful preparation, correct electrode selection, and disciplined technique, provides a reliable method for repairing cracks and defects in metal structures ranging from farm equipment to industrial steelwork. The combination of proper cleaning, preheating, multiple-pass procedures, and post-weld inspection ensures that repairs restore the original strength and service life. With the expanded knowledge of troubleshooting and safety, welders can approach challenging repair jobs with confidence and produce long-lasting results. Continued learning and practice—along with adherence to standards from organizations like the American Welding Society and OSHA—will refine skills and ensure every repair meets the highest quality and safety standards.