What SMAW is and why welders use it

SMAW stands for Shielded Metal Arc Welding, a process where an electrode — a metal rod coated in flux — melts to join two pieces of metal together. The flux coating burns away as you weld, creating a gas cloud that shields the molten metal from oxygen and other elements in the air. Without that shield, the weld would become brittle and weak. SMAW is one of the oldest and most widely used welding processes in construction, structural steel work, pipeline fabrication, and maintenance repair.

The process is popular because it works outdoors in wind and rain better than some alternatives, requires relatively straightforward equipment, and can join thick metals that other processes struggle with. A welder holds a handheld electrode holder connected to a power source, strikes an arc between the electrode and the workpiece, and moves the electrode along the joint while the metal pools and cools behind it. The slag — the hardened flux residue — must be chipped away after each pass to see the weld underneath and prepare for the next layer.

Key Takeaways

  • SMAW uses a coated metal electrode that creates its own shielding gas as it burns, making it effective in outdoor and windy conditions where other processes fail.
  • The process requires striking an arc, maintaining proper travel speed and angle, and removing slag between passes — skills that take practice to develop consistently.
  • Equipment needs include a power source (AC or DC), electrode holder, ground clamp, and a variety of electrode types matched to the metal being welded and the joint position.
  • SMAW produces stronger welds in thick materials and can work on rusty or dirty surfaces better than processes like MIG or TIG welding.
  • The main drawback is the slag removal step and lower deposition rates compared to newer processes, which makes it slower for high-volume production.

The equipment you need to run SMAW

A SMAW setup starts with a power source — either AC (alternating current) or DC (direct current). AC machines are cheaper and work well for general structural work. DC machines offer better arc stability and are preferred for pipe welding and precision work, but cost more. The power source connects to an electrode holder (the handheld clamp that grips the electrode) and a ground clamp (also called a work clamp), which attaches to the workpiece to complete the electrical circuit.

You also need a steady supply of electrodes — the consumable metal rods that do the actual welding. Electrodes come in different diameters (typically 1/16 inch to 5/32 inch) and are classified by their flux coating and the type of metal they deposit. A 6010 electrode, for example, deposits mild steel and works well for vertical and overhead positions. A 7018 electrode deposits mild steel with a low-hydrogen coating, preferred for structural work where strength matters most. The electrode classification tells you what metal it deposits, what positions it works in, and what current type and range to use.

Personal protective equipment includes a welding helmet with a dark lens (shade 10 to 14, depending on amperage), welding gloves, a leather apron, and steel-toed boots. The helmet protects your eyes from the intense ultraviolet and infrared radiation the arc produces — looking at an unshielded arc causes arc eye, a painful burn to the cornea that can happen in seconds.

How the arc is struck and maintained

Striking the arc is the first skill a SMAW welder learns, and it takes repetition to do smoothly. You position the electrode tip about 1/8 inch above the workpiece at a slight angle, then either scratch it across the surface (like striking a match) or tap it lightly downward until the arc ignites. Once the arc is live, you pull the electrode back to maintain a gap of roughly 1/8 inch — too close and the electrode sticks to the workpiece; too far and the arc dies. The arc temperature reaches about 6,500 degrees Fahrenheit, hot enough to melt both the electrode and the base metal into a molten pool.

As you move the electrode along the joint, you must maintain three things at once: the correct travel speed (fast enough to avoid a wide, weak bead, slow enough to fuse properly), the correct angle (usually 15 to 45 degrees depending on position and joint type), and the correct arc length. Beginners often move too fast, creating a thin, ropy bead that lacks fusion. Others move too slowly, building up too much heat and causing the base metal to sag or burn through. The welder's hand and arm do most of the work, while the body stays stable and the eyes stay focused on the arc and the pool shape.

Slag removal and multi-pass welding

After each pass — each single run of the electrode along the joint — the flux coating has turned into slag, a hard, glassy layer that sits on top of the weld bead. This slag must be removed before the next pass can be laid down, or the new metal will not fuse properly to the old. Removal is done with a slag hammer (a small hammer with a flat face and a pointed or chiseled end) and sometimes a wire brush. The welder chips away the slag, then brushes the bead clean so they can see the weld surface and prepare for the next layer.

Thick materials often require multiple passes — sometimes five, ten, or more layers of weld metal stacked on top of each other. Each pass must be cleaned and inspected before the next one begins. The order and pattern of passes matters: for a thick butt joint (two pieces joined end-to-end), the first pass might be a small root bead that penetrates deep into the joint, followed by fill passes that build up the height, and finally a cap pass that smooths and finishes the surface. This layering ensures the weld is strong throughout its depth, not just on the surface.

SMAW versus other welding processes

SMAW differs from MIG welding (Metal Inert Gas), which uses a wire electrode and an external shielding gas. MIG is faster and produces less slag, but it does not work well outdoors in wind because the gas shield blows away. SMAW's self-shielding flux makes it the standard for field work and outdoor construction. SMAW also differs from TIG welding (Tungsten Inert Gas), which uses a non-consumable tungsten electrode and a separate filler rod. TIG produces cleaner, stronger welds and works on aluminum and stainless steel, but requires more skill and is slower than SMAW.

For thick structural steel, heavy pipe, and outdoor repair work, SMAW remains the most practical choice. It handles rusty, dirty, or painted surfaces better than MIG or TIG because the flux helps clean the joint as it melts. The downside is the slag removal step and lower deposition rates — you lay down less metal per hour than with MIG or flux-core processes. In high-volume fabrication shops, faster processes often replace SMAW. But for one-off jobs, field repairs, and situations where equipment portability and weather resistance matter, SMAW is still the industry standard.

Common mistakes and how to avoid them

New SMAW welders often strike the arc too hard or at the wrong angle, causing the electrode to stick to the workpiece instead of igniting cleanly. The fix is practice: strike with a light tap or scratch, not a heavy blow. Another common error is moving the electrode too fast, which leaves a thin, weak bead with poor fusion. Slowing down and watching the molten pool — it should be roughly the same width as the electrode diameter — helps. Conversely, moving too slowly causes excessive heat buildup, which can burn through thin material or create a bead that is too wide and weak.

Improper electrode angle is another frequent problem. The electrode should be angled slightly into the direction of travel (pushing angle) for most flat and horizontal work, or angled back slightly (dragging angle) for vertical and overhead positions. Holding the electrode perpendicular to the workpiece (straight up and down) often produces poor fusion and a weak bead. Finally, failing to remove slag thoroughly before the next pass traps flux residue inside the weld, creating voids and weak spots. Taking time to chip and brush each bead clean, even though it slows the work, produces stronger, more reliable welds.

Electrode selection and current settings

Choosing the right electrode depends on three factors: the type of metal being welded, the position of the joint, and the thickness of the material. Mild steel electrodes like 6010 and 7018 are the most common. The 6010 is versatile and works in all positions but produces a rougher bead. The 7018 is low-hydrogen, meaning it produces fewer hydrogen-related defects, and is preferred for structural work where code compliance and strength are critical. For stainless steel, you would use a stainless electrode like 308 or 316. For cast iron, a nickel-based electrode like ENiFe-CI is needed.

Current settings — the amperage — depend on the electrode diameter and type. A 1/16-inch electrode typically runs at 40 to 80 amps, while a 5/32-inch electrode might run at 150 to 200 amps. The electrode packaging always lists the recommended amperage range. Too little current and the arc is weak, the bead is thin, and fusion is poor. Too much current and the electrode melts too fast, the arc becomes unstable, and the base metal can burn through. Most power sources have a dial or digital display to set the amperage, and experienced welders adjust it slightly based on how the arc sounds and feels — a good arc has a steady, crackling sound and a stable pool.

Frequently Asked Questions

What does the coating on a SMAW electrode do?

The coating, called flux, serves multiple purposes: it creates a shielding gas as it burns to protect the molten metal from oxygen, it helps clean the joint surface, it stabilizes the arc, and it produces the slag layer that protects the cooling weld. Different flux types produce different properties — some are fast-freezing for vertical work, others are all-position, and some are low-hydrogen for high-strength applications.

Can SMAW be used indoors?

Yes, SMAW works indoors and outdoors. However, the slag and spatter it produces require good ventilation to avoid fume buildup. In enclosed spaces, a fume extraction system or good air circulation is necessary. Outdoors, SMAW is preferred because it is not affected by wind like gas-shielded processes.

How long does it take to become proficient at SMAW?

Basic competency — striking an arc, running a straight bead, and producing sound welds in flat position — typically takes a few weeks of practice. Mastery of all positions (flat, horizontal, vertical, overhead) and ability to pass certification tests takes several months to a year of regular practice and formal training.

What is the difference between AC and DC power for SMAW?

AC (alternating current) is cheaper and works well for general structural work. DC (direct current) offers better arc stability and control, especially for pipe and precision work, but costs more. Some electrodes work on AC only, others on DC only, and some on both — the electrode packaging specifies which.

Why does slag need to be removed between passes?

Slag is a non-metallic residue that does not bond to the base metal or the next pass of weld metal. If left in place, it creates a weak layer inside the weld that can cause the joint to fail under stress. Removing it ensures each new pass fuses properly to the previous one.