Even skilled welders occasionally encounter problems. From ugly beads to weak joints, welding defects can ruin your work, compromise safety, and waste time and materials.
Whether you’re a DIY welder or just getting started, learning how to spot and avoid the most common welding issues will help you get stronger, cleaner, and more reliable results.
Let’s break down the most frequent welding defects, how to recognize them, and (most importantly) how to prevent them.
1. Porosity (Tiny Holes in the Weld)
What it looks like: Small bubbles or pinholes on or inside the weld
Why it happens: Contaminated base metal, dirty filler, damp electrodes, or poor gas shielding. Other common causes include an improper gas nozzle, excessive arc length, or high humidity during welding.
How to avoid it:
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Clean the metal thoroughly before welding (remove oil, paint, rust)
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Use dry, properly stored rods or wire
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Check gas flow and shielding coverage if using MIG or TIG
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Avoid drafts in your welding area
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Don’t touch the filler wire with your bare hands
2. Cracks
What it looks like: Obvious fractures in or near the weld may appear immediately or after cooling
Why it happens: High heat input, rapid cooling, poor joint design, or wrong filler metal
How to avoid it:
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Preheat thicker materials before welding
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Use proper filler metal (especially for dissimilar metals)
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Avoid sharp corners—design joints with smooth transitions
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Control heat input to prevent overheating and shrinkage stress
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Don’t weld over dirty or contaminated surfaces
3. Undercut
What it looks like: A groove along the base metal at the edge of the weld bead
Why it happens: Too much heat, fast travel speed, poor electrode angle, or poor manipulation technique (such as incorrect weaving pattern)
How to avoid it:
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Lower the amperage if the weld is too hot
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Slow down slightly to allow for better filler deposit
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Keep your electrode or torch angle consistent (about 10–15° push for MIG)
4. Lack of Fusion
What it looks like: The metal doesn't bond properly across surfaces; the weld bead appears to sit on top of the base metal without fully melting into it.
Why it happens: Not enough heat, dirty metal, wrong technique
How to avoid it:
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Clean your base metal thoroughly
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Increase the amperage slightly or slow down the travel speed
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Maintain a short arc length (especially with TIG and Stick)
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Use the correct electrode or filler for the metal type
5. Incomplete Penetration
What it looks like: The weld doesn't extend deep enough into the joint thickness, often failing to reach the root, especially in thicker material.
Why it happens: Low heat input, poor joint design, or fast travel speed
How to avoid it:
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Use proper joint prep (groove or bevel for thick pieces)
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Adjust the amperage based on material thickness
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Consider multiple passes for thicker welds
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Keep your travel speed steady and not too fast
6. Excess Spatter (MIG/Stick)
What it looks like: Small metal droplets stuck around the weld bead
Why it happens: Incorrect voltage, poor technique, or wrong shielding gas
How to avoid it:
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Fine-tune voltage and wire feed speed on your MIG welder
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Use anti-spatter spray or gel if needed
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Maintain a consistent distance and angle from the workpiece
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Use correct gas mix—tri-mix or 75/25 argon/CO₂ for stainless or mild steel
7. Slag Inclusion (Stick or Flux-Core MIG)
What it looks like: Non-metallic material (slag) trapped inside the weld, leading to weak spots and potential failure.
Why it happens: Not cleaning between passes, improper rod angle, low welding current, slag trapped in deep grooves, overly fast travel speed, or poor joint preparation that prevents slag from escaping.
How to avoid it:
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Chip and wire brush all slag between weld passes
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Use proper rod angle (typically 10–15° drag for Stick)
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Maintain a steady, appropriate travel speed
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Ensure your amperage is high enough to keep the puddle fluid
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Prepare joints properly with clean bevels or grooves to allow slag to escape
Quick Reference: Common Defects at a Glance
Pro Checklist for Cleaner Welds
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Practice on scrap metal before tackling your final project
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Dial in your machine settings, every welder is a little different
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Inspect each weld visually before moving on
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Keep your workspace clean and well-ventilated
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Invest in proper safety gear and tools; they pay off over time
At the end of the day, welding is a skill, and mistakes are part of the learning process. But understanding what causes defects and how to prevent them will accelerate your growth and lead to better, stronger welds.
Looking for the right tools and consumables? Explore trusted brands like Miller, Lincoln, Canaweld, and ESAB at Canada Welding Supply, your premier source for welding equipment, filler metals, and accessories.