Cracking, burn-through, and spatter are common SMAW weld defects you should understand.

Welding is part art, part science, and a whole lot of hands-on feel. If you’ve spent time in a shop, you’ve seen what a good weld looks like and you’ve also spotted the weak spots—the little flaws that can grow into big problems. When people ask, “What’s the most common weld defect?” the quick, honest answer is a bit of a head-scratcher, because there are a few frequent troublemakers. Still, cracking often tops the list as a curb-stopper for joint strength. Let’s unpack why that is, and what else tends to show up in everyday welding.

Cracking: the quiet, stubborn enemy

Cracking is exactly what it sounds like—a fracture that appears in the weld metal or the heat-affected zone (HAZ). It can feel sneaky because it might not be obvious right away. You heat, you melt, you join, and if the conditions aren’t right, a crack can form as the metal cools and tightens. There isn’t just one flavor of crack either. You’ll hear about hot cracks, which show up while the metal is still hot; cold cracks, which appear after it’s cooled; and reheat cracks, which can show up when the welded piece is later heated again during service or post-weld processes.

Why does cracking happen? There are several contributing factors, and they often work in concert:

• Thermal stresses. Metals expand when hot and contract when cool. In a welded joint, the metal next to the weld heats up fast and wants to expand, but the cooler surrounding metal resists that change. The mismatch creates tensile stresses that can pull the material apart.

• Material fit and quality. If the base metal and filler metal don’t play nicely together—think different strengths, different grain structures, or incompatible chemical makeup—the joint can become a weak link that cracks under stress or during cooling.

• Hydrogen-related cracking. Hydrogen can migrate into steel during welding if certain conditions aren’t controlled (moisture, damp coating, or overly long arc exposure, to name a few). Hydrogen embrittlement shows up as cracks that can travel through the weld or the surrounding heat-affected zone.

• Restraint and geometry. A joint that’s tightly restrained or has unusual geometry can trap stress. Think about a fixed plate welded to another piece with little room to move as it heats and cools; those stresses have nowhere to go but into the metal itself.

Understanding cracking isn’t about fear—it’s about awareness. If you know cracking is a risk, you’re better prepared to prevent it. And here’s the good news: many root causes are addressable with the right technique and preparation.

Burn-through and spatter: the other two culprits we notice

Burn-through is exactly what it sounds like—metal holes created by too much heat. When the heat input is excessive for the thickness of the material, the weld can burn through, leaving a hole that compromises the joint. It’s a sign you’ve pushed the heat input a notch too high relative to the workpiece, or you’ve held the arc in a place a touch too long.

Excessive spatter is the other common nuisance. Molten droplets landing outside the weld pool create a rough, pitted surface and can interfere with fit-up, corrosion resistance, and aesthetics. Spatter isn’t usually a threat to the joint’s strength, but it’s a sign that the process isn’t well controlled. It can also lead to adhesion issues if you’re coating or painting over the weld later.

Spotting these defects on the shop floor isn’t just a matter of a quick glance. It’s about reading the signs and knowing what to adjust. Burn-through shows up as holes or thinning in the base metal right at or near the weld. Spatter shows up as scattered metal beads on the surface and, if left, can trap moisture or debris. A careful eye also notes porosity, improper fusion, or undercut—each defect with its own story and its own fix.

How to tell a good weld from a not-so-good one

Let me explain how you can develop a sixth sense for weld quality, because seeing is believing in this trade. A strong weld should feel solid to tapping, have a consistent bead with uniform ripples, and present a smooth face without cracks or pits. The bead should feather into the base metal rather than leave a jagged edge. If you poke at it with a file and you’re suddenly chasing a rough surface or a visible gap, that’s a sign to slow down and reassess.

Here are some practical checks you can perform in a typical shop setting:

• Look at the bead. Is it uniform in width and height? Do the ripples look even along the joint? A wavy bead or a bead with inconsistent width often points to issues with travel speed or current control.

• Check the root. For many SMAW joints, proper penetration is essential. A shallow root or excessive lack of fusion at the root can be a red flag that heat input or technique needs adjustment.

• Inspect for cracks and porosity. Hairline cracks may be easy to miss at first glance; a bright light and a careful feel with a chisel or a file can reveal hidden flaws. Porosity shows up as small voids or gas pockets in the weld metal.

• Surface blemishes. A bit of spatter is common, but heavy spatter or drips indicate improper arc length, improper amperage, or poor electrode selection for the material/position.

• Mechanical checks. If you can, perform a simple bend test or cross-section the joint to view the fusion line. While this isn’t always practical on every job, it’s a powerful diagnostic tool when you’re learning.

Prevention: tuning the process for reliable joints

The line between a flawless weld and a flaw is often a line you can redraw with a few careful adjustments. Here are some practical tactics that work across many SMAW tasks:

• Heat input control. Too much heat is a sure-fire path to burn-through and cracking. Too little heat, and you risk poor fusion. The trick is finding the middle ground for the material thickness and the electrode you’re using. This means selecting the right amperage, travel speed, and electrode angle for each weld.

• Preheating when needed. For thick sections or certain steels, preheating can dramatically reduce the risk of cracking by slowing the cooling rate. Preheat isn’t a sign you’re doing something wrong; it’s a smart move to keep the joint from becoming brittle as it cools.

• Interpass temperatures. Some steels crave a specific window between passes. If you let the joint cool too much between passes, you can set yourself up for cold cracking later in service. A controlled, moderate interpass temperature helps keep the metal ductile enough to absorb stress.

• Joint fit-up and cleanliness. A clean, properly gapped joint is a foundation stone. Dirt, oil, oxide, and misalignment all increase the risk of poor fusion and defects.

• Electrode choice and condition. Electrodes aren’t one-size-fits-all. The coating composition, cellulosic vs. rutile types, and storage condition all influence the heat characteristics and hydrogen content of the weld. Keep electrodes dry, out of humidity, and up to date with the right type for the metal you’re welding.

• Technique and consistency. A steady hand matters, but so does the cadence of your travel and the arc length. A consistent travel speed and a stable arc help produce uniform beads and fewer defects.

The human side of welding: practice, but with purpose

Welding isn’t only about the machine and the metal; it’s about how you think through the joint from the moment you start the arc. It’s a bit of problem-solving mixed with a careful craft. You measure, you predict, you adjust on the fly. And yes, you can develop a good eye for when the heat feels off, or when a joint isn’t fitting together as it should.

For many students and new welders, those early sessions can feel like a dance you’re still learning. You’ll experiment with angles, you’ll test different electrode types, and you’ll learn to read the telltale signs of a developing flaw. That learning curve is normal. What matters is you’re building a mental checklist you can rely on—one that lets you decide when to slow down, when to change technique, and when to re-check fit-up before you strike again.

Analogies that keep it human

Think of a weld like a bridge between two shores. The base metals are the shoreline; the filler metal is the bridge deck. If the land on one side shifts or the deck isn’t continuous, the bridge won’t hold its load. Cracking is like a crack in the deck or the arch—the first sign that stress found a weak point. Burn-through is the hole in the deck where too much heat carved through. Spatter is the gravel that lands on the road, making the ride rough and needing extra cleanup before traffic can pass.

In the shop, these are not just defects; they’re messages. They tell you something about heat, speed, and how well the materials interact. If you learn to read those messages, you’ll catch problems before they become costly repairs or, worse, safety concerns.

A few closing reminders that stick

• Cracking is common enough to take seriously. Understanding the forms and why they happen helps you prevent them.

• Burn-through and spatter are telltale signs that heat control and technique could be improved. Don’t ignore them; use them as diagnostics.

• Preparation beats correction. Cleanliness, fit-up, and correct electrode choice set you up for success before you even strike the arc.

• Preheating and interpass temperature aren’t excuses; they’re practical tools in the right situations.

• Practice with purpose. Each weld teaches you something about heat, metal, and how they behave as a pair under stress.

A quick stroll through real-world welding life

If you’ve ever watched an experienced welder at work, you’ll notice the obvious: there’s a rhythm, a cadence, and a sense of when to push forward and when to pause and re-check. The best welders aren’t the ones who push hardest; they’re the ones who manage heat and time with intention. They know when to switch to a different electrode for a better fusion, when to back off a touch to avoid burn-through, and how to clean the joint properly so nothing derails the bead.

And yes, you’ll hear stories about strange cracks showing up in places you wouldn’t expect—stories about thick welds in highly restrained joints or about steels with tricky alloying elements. Those moments become lessons: a reminder that materials aren’t just blocks of metal; they carry histories, microstructures, and a whole set of rules that influence how they behave in the heat of the moment.

Bottom line

In the world of SMAW, cracking stands out as a common and impactful defect, but it’s not the only one. Burn-through and spatter show up with their own fingerprints and consequences. What ties them together is the thread of control: control of heat, control of fit, control of technique, and control of cleanliness.

If you’re making your way through welding school or just starting out in a shop, keep this simple compass in your pocket:

• Watch the heat like a hawk. Too much or too little both spell trouble.

• Fit and clean your joints. A good base makes your welds stronger.

• Choose the right electrode for the job and keep it dry.

• Look, listen, and feel. The bead tells you a lot about what’s happening in the metal.

With that mindset, you’ll be building joints that aren’t just welded—they’re strong, reliable, and ready to take on whatever work comes next. And when you do spot a crack or a spatter pattern, you’ll know what to adjust, how to fix it, and why it matters for the whole piece.

If you’re curious to hear more about how different metals interact in SMAW, or you want a few real-world examples of how a slight tweak in heat can change a weld’s outcome, I’m happy to share. After all, welding is as much about learning from what you see as it is about wielding the arc.