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What porosity in a stick weld looks like

Porosity is gas trapped in solidifying weld metal. On a stick weld, it may show up as pinholes on the bead surface, a rough crater at the stop, or cavities revealed after you chip the slag. A cluster of small pores is often called wormholing when the openings form elongated tracks.

Do not confuse every dark spot with porosity: leftover slag can look similar. Brush and chip the bead clean before judging it. Surface pores are a warning, not proof that the full weld is defective. But a porous weld can have less effective cross-section and may fail inspection or leak, so do not simply cover it with another pass.

Find the source before repairing

Porosity usually comes from contamination, moisture, poor shielding, or an incorrect setup. Check the whole joint and the area around it—not just the hole. Paint, oil, rust, mill scale, moisture, and residues from cleaners can release gas in the arc. Wind can disturb the shielding gas produced by the electrode coating, especially outdoors. A long arc, wrong polarity, damp electrodes, or an electrode being stored badly can also contribute.

Start with the basics: confirm the electrode type and polarity from its packaging, set current within the maker’s range, and keep a steady, short arc. As a rough reference, a 1/8-inch E7018 is commonly used around 100–140 amps, but the correct setting depends on position, machine, and electrode brand. Do not use that range as a substitute for the package instructions. If the defect appeared suddenly, suspect a changed condition—wet stock, a new rod container, wind, or a loose work connection—before changing several settings at once.

Make the repair safely

Let the work cool enough to handle, then remove slag and inspect the full affected area. Wear a welding helmet with the correct shade, safety glasses under it, gloves, flame-resistant clothing, and hearing protection when grinding or chipping. Keep sparks away from combustibles, and do not weld containers or enclosed parts that may hold flammable or toxic residues. Use ventilation appropriate to the material and coating; galvanized steel, for example, needs particular care because its fumes are hazardous.

For a critical structural, pressure, or code-regulated weld, follow the approved repair procedure and inspection requirements. Do not assume a visually tidy repair is acceptable. If you cannot identify the material or the required procedure, get qualified advice before grinding or rewelding.

Remove the porous metal

Grind or gouge out the defective weld metal until you reach sound, solid metal. A small surface pore may only require local removal, but a line of pores, repeated pinholes, or a cavity exposed beneath the surface calls for a wider excavation. Check the bottom and edges closely; pores left in the joint can reopen in the repair pass.

A 4-1/2-inch angle grinder with a suitable grinding wheel is adequate for many small repairs. A grinder is inexpensive and versatile, but it removes metal more slowly and can round edges if rushed. For longer or deeper excavations, an air carbon-arc gouging setup is faster, but it costs more, removes metal aggressively, and requires good control and hearing and eye protection. A 4-1/2-inch angle grinder is usually the practical choice for occasional shop repairs; gouging equipment makes more sense for frequent heavy work.

Use a fresh, uncontaminated grinding surface. Avoid using a wheel that has picked up oil or been used on a different alloy where cross-contamination matters. After excavation, brush and clean the groove, then inspect it under good light. The opening should have clean edges and enough room for the electrode to reach the root. Do not leave a sharp, narrow slot that traps slag.

Prepare and reweld

Remove paint, grease, rust, scale, and moisture from both sides of the repair area as far as practical. Use a clean wire brush and a suitable solvent only if it is safe for the material and fully evaporated before welding. Keep the work dry. If moisture is the suspected cause, do not try to compensate by turning up the amperage.

Choose an electrode suited to the base metal, position, and service. Low-hydrogen rods such as E7018 need dry storage and may require a holding oven after opening; follow the manufacturer’s instructions rather than guessing at a bake temperature. For occasional noncritical work, a properly stored general-purpose rod may be simpler, but it is not an interchangeable substitute where the job specifies low-hydrogen consumables. A low-hydrogen 7018 electrode is useful when the procedure calls for it, provided you can store it correctly.

Run a short, controlled pass with the arc close to the work. Keep a consistent travel speed and avoid stopping over the defect; fill the crater before breaking the arc. Chip and brush slag between passes, and inspect each layer before adding the next. If porosity returns, stop and troubleshoot rather than burying it.

Match the symptom to the likely cause

Verify the finished repair

After the final pass cools, remove all slag and inspect the bead and tie-ins for pinholes, cracks, undercut, and incomplete fusion. If a pore remains, grind it out and repeat the repair; a cover pass is not a fix. For noncritical work, a careful visual check may be enough. For pressure boundaries, lifting equipment, structural connections, or regulated work, use the specified inspection method and acceptance criteria—visual inspection cannot reveal every internal defect.

The cheapest reliable repair is usually the one that fixes the cause as well as the hole: clean metal, dry and suitable electrodes, stable arc conditions, and complete removal of unsound weld. Repeated grinding and rewelding without correcting those conditions wastes time and can leave the joint thinner than it was before.