MMA welding: how stick welding actually works

Process 111 in the EN ISO 4063 numbering, SMAW in the American one, and "stick" everywhere else. The oldest arc process still in daily use, and on site still often the best one.

What happens at the arc

An arc burns between the metal core of the electrode and the workpiece at roughly 6000 °C. The core melts and crosses the arc as droplets. The coating melts too, and it is the coating that does the clever work: it releases gas that displaces air from the arc, it forms slag that floats on the pool and protects it while it cools, it stabilises the arc electrically, and it carries alloying elements into the weld.

That is why a stick electrode is not simply wire with a covering. Change the coating and you change the process: its penetration, its hydrogen level, the positions it can work in and the current it wants.

The coating decides everything

Rutile electrodes strike easily, run on AC or DC, give a smooth bead and slag that peels off almost by itself. They are the ones to learn on and the ones for general fabrication. Their weakness is hydrogen: they carry more of it than basic types.

Basic electrodes give tough, low-hydrogen weld metal and are what structural and pressure work calls for. They also strike badly, need DC+, run a stiffer arc and must be kept dry. Every welder who has cursed at an electrode that would not light was probably holding a damp basic one.

Cellulosic electrodes make a deeply penetrating, violent arc that can be run downhill at speed. They are the pipeline root-run electrode and almost nothing else.

The differences are set out in full in electrode coating types.

Setting up

Current comes from the diameter — 30 to 40 A per millimetre, less for vertical and overhead. The current calculator applies the corrections, and the table gives the same figures for the wall.

Arc length is the parameter nobody sets on the machine and everybody controls with their hand: keep it roughly equal to the core diameter. Too long and the arc pulls air in, giving porosity and spatter; too short and the electrode freezes into the joint.

The travel angle is 5 to 15° from vertical, dragging — the electrode leans back the way you came, so the arc force pushes the slag behind the pool instead of over it. Slag that runs ahead of the pool gets trapped and becomes an inclusion.

When MMA is still the right choice

Outdoors and in wind, because there is no gas shield to blow away. On rusty, painted or galvanised steel, where a basic electrode will still make a sound weld. On site, where the equipment is one box and two leads and nothing needs a trolley. On repairs, where the exact grade of the parent metal is unknown and a forgiving process matters more than deposition rate.

Where it loses is productivity: arc-on time is 25 to 35 % because of electrode changes and slag removal, against 40 to 55 % for MIG/MAG. In a shop with repeat work that difference decides the process, and the cost per metre makes it visible.

The four mistakes that show up in every weld test

• Current too low. A narrow, high bead sitting on the plate, slag that will not release, and an electrode that keeps sticking.
• Arc too long. Spatter everywhere, a wide flat bead and porosity from the air pulled into the arc.
• Wrong angle. Slag running ahead of the pool, which ends up trapped in the weld as an inclusion.
• Damp electrodes. Porosity on the surface and, on restrained joints in higher-strength steel, cold cracks a day later.

Updated: 13 August 2026