How to Read a Weld Bead: Defects & Fixes 

The weld bead is the most honest feedback you’ll ever get. It doesn’t soften the truth, it doesn’t spare your feelings, and it doesn’t care how long you’ve been welding. Every bead you run is a report card on what you did in the previous thirty seconds — settings, technique, travel speed, angle, and prep all written right there in steel.

Learning to read that feedback is one of the highest-leverage skills you can develop as a welder. It’s the difference between running twenty bad beads wondering what’s wrong and adjusting after three. Every experienced welder has internalized this — it’s a big part of what separates them from a beginner who’s been at it for the same amount of time.

This guide covers the most common bead defects, what each one tells you, and what to change to fix it. MIG examples are primary since that’s where most readers are starting, but the diagnostic logic applies across processes. Here is a quick setup guide to get you on the right track.

Pro Tip: After every practice bead, stop and look at it before you run the next one. Don’t just glance — flip it over, look at both sides if you can, run your finger along it (after it cools). One bead observed carefully teaches you more than ten beads run on autopilot.

What a Good Weld Bead Looks Like

Before you can diagnose problems, you need a reference point. Here’s what a correct MIG bead on mild steel looks like:

• Width is consistent from start to finish — no wide spots, no narrow spots
• Height is uniform — slightly raised above the base metal, convex but not piled up
• The edges (toes) tie in smoothly to the base metal with no gaps or undercut
• The ripple pattern is consistent — evenly spaced, similar in size throughout
• Color is a consistent silvery-gray — not black, not blue-purple in large patches
• Spatter is minimal — a few small balls around the bead is normal; a blast zone is not

That’s the target. Everything below is what happens when something is off, and what to do about it.

Bead Too Wide and Flat

What it looks like: The bead spreads out much wider than normal, lies flat or slightly concave against the base metal, and the toes may blend in aggressively or even undercut.

What it means: Too much heat. The most common causes are amperage set too high, travel speed too slow (or both). The puddle is too hot and too fluid, and it’s spreading out rather than building up.

What to change: Increase travel speed first — moving faster reduces heat input without changing machine settings. If the bead is still wide and flat, reduce voltage by one step. Do one thing at a time so you can isolate what’s actually causing it.

Pro Tip: Travel speed is the most underused adjustment in a beginner’s toolkit. Most new welders move too slowly, which puts too much heat into the part. If your bead looks wrong, try moving faster before you touch the machine settings.

Bead Too Narrow and Piled Up (Ropy Bead)

What it looks like: The bead sits high on the surface, narrow, and almost rope-like. The edges don’t tie into the base metal — the bead looks like it’s sitting on top rather than fused into the material.

What it means: Not enough heat. Low voltage, wire feed speed too fast for the voltage setting, or travel speed too fast. The metal is depositing without proper fusion into the base material.

What to change: Increase voltage one step. If the bead is still ropy, slow down your travel speed slightly. On a ropy bead where the edges clearly aren’t tying in, also check that your work clamp is making good contact — a bad ground causes erratic, cold-looking welds.

Porosity — Holes in the Bead

What it looks like: Small round holes visible on the surface of the bead, or you break a bead and see a Swiss cheese cross-section inside. Ranges from a few pinholes to severe internal voids.

What it means: Contamination. Gas porosity is caused by atmospheric gas (nitrogen, oxygen) getting trapped in the weld pool. Common causes: shielding gas problems (low flow, leak, blown away by wind), contaminated base metal (rust, paint, oil, mill scale), or contaminated wire or electrode.

What to change: MIG: check your shielding gas flow rate (15–20 CFH for most indoor applications), check for leaks at the regulator and gun connections, make sure there’s no air movement blowing the shielding away. Also clean the base metal thoroughly — porosity from contamination looks the same as porosity from gas issues and the fix is different.

Stick: E7018 porosity is almost always a moisture problem — the rods absorbed humidity from the air. Low-hydrogen rods must be stored sealed or in a rod oven. Switch to a fresh, properly stored rod and the porosity should clear up immediately. Another possible spot for porosity is at your start when you strike in. Common practice with 7018 is to strike in before your start, drag back to your starting location, then burn through your initial start to get any possible porosity out.

Fun Fact: Porosity was such a persistent problem in early industrial welding that the American Welding Society developed some of its first inspection standards specifically to define acceptable porosity limits in structural welds. The standards are still in use today — AWS D1.1 defines maximum allowable porosity for structural steel fabrication.

Undercut

What it looks like: A groove or channel along one or both edges of the bead — the base metal is eroded away at the toes of the weld rather than built up. Undercut looks like the bead has chewed into the surrounding material.

What it means: Too much heat at the edges, or gun angle is directing the arc into the base metal instead of into the puddle. Common with high amperage and fast wire feed speed, or with an incorrect work angle pushing the arc to one side. Could also be due to not holding your edges to let the metal fill in before moving on.

What to change: Reduce amperage or voltage slightly. Check your gun angle — for a flat bead, the work angle should be roughly 90° to the joint with a 10–15° drag angle (pointing back toward the completed weld). Slowing down travel speed can also help, as it lets the puddle fill in the eroded area before you move on.

Spatter — Everywhere

What it looks like: Small balls of metal stuck to the base metal around the weld, sometimes up to several inches away. Some spatter is normal in MIG — a blast zone isn’t.

What it means: Several possible causes: voltage too low for the wire feed speed (most common), running in short-circuit transfer at the edge of the operating window, contaminated base metal, or incorrect shielding gas. On stick, excessive spatter is usually an arc length problem — too long.

What to change: MIG: increase voltage one step, or decrease wire feed speed slightly. Make sure your liner and contact tip are in good condition — a partially blocked liner creates irregular wire feeding that shows up as spatter. Anti-spatter spray on the surrounding metal saves cleanup time but doesn’t fix the underlying issue.

Inconsistent Bead Width (Wandering, Wavering)

What it looks like: The bead changes width along its length — sometimes wide, sometimes narrow, with no apparent pattern. The ripple spacing may also be inconsistent.

What it means: Travel speed variation. This is almost always technique, not machine settings. The welder is speeding up and slowing down unconsciously.

What to change: Focus on body position and work support. The most consistent beads come from welders whose arms are well-supported and whose travel speed is controlled by body movement rather than just wrist movement. Practice on flat plate until your speed is consistent before moving to awkward positions.

Burn-Through

What it looks like: A hole through the base metal, or the material is clearly melted through and sagging or falling through.

What it means: Too much heat for the material thickness. Especially common on thin material (under 1/8″) with settings appropriate for thicker stock, or when welding over a gap that’s larger than the material can bridge.

What to change: Reduce voltage, increase travel speed, or both. On thin material, consider using a push technique (angling the gun forward in the direction of travel) rather than drag — it puts slightly less heat into the base metal. Stitch welding (short welds with gaps) also controls heat input on thin material.

Cold Lap (Lack of Fusion)

What it looks like: The bead appears to sit on top of the joint or previous pass without truly melting into it — the surface can look acceptable, but the metal underneath isn’t fused. It often only shows up when the joint is bent, machined, or stressed and the weld separates cleanly along the unfused line.

What it means: Not enough heat to melt the base metal (or the previous pass, on multi-pass welds) before new filler lands on top. Common causes: travel speed too fast, amperage or wire feed speed mismatched for the joint thickness, an incorrect gun angle that skates the arc across the surface instead of into the joint, or scale, oxidation, and slag left on the surface from a prior pass.

What to change: Slow down your travel speed first to give the arc more time to melt the joint. If the bead still isn’t fusing, increase voltage one step. On multi-pass welds, grind or wire-brush between passes to remove slag and oxidation — the new pass can’t fuse to a surface it can’t reach.

The Diagnostic Table

Quick reference for the most common bead problems:

The Sound of the Arc

Experienced welders read the arc by sound as much as by sight. MIG welding should sound like steady frying — the constant sizzle of eggs in a pan, consistent and smooth. That’s the sound of a stable arc in short-circuit transfer.

Popping, crackling, or stuttering sounds mean the arc is unstable. Common causes: wire feed issues (check tension, liner condition, contact tip), bad ground connection, or settings at the edge of the stable operating window.

A buzz or hum with good bead appearance means you’re in spray transfer (higher voltage and wire feed territory) — that’s fine and intentional at higher settings on thicker material and with the proper shielding gas.

Train yourself to hear the difference. Once you know what good sounds like, bad becomes obvious before you even look at the bead.

A Practice Plan for Bead Reading

Here’s a focused practice session for developing bead-reading skills:

• Cut 6″ x 6″ mild steel coupons from 1/8″ or 3/16″ plate — 10 of them if you can.
• Set your machine to normal settings and run a flat bead. This is your baseline.
• Deliberately change one variable — increase voltage by one step, run a bead. Decrease voltage, run a bead. Speed up travel, slow down travel. Run each bead on a fresh coupon or clearly spaced.
• Label each bead with a marker (masking tape on the back works) noting what you changed.
• Compare them side by side. The differences are dramatic once you’ve created them intentionally.

Deliberately creating bad beads to understand what they look like is one of the fastest ways to develop your diagnostic eye. Most beginners only see bad beads by accident — you’ll understand them much faster if you create them on purpose.

The Bottom Line

The bead doesn’t lie. Every visible defect has a specific cause, and almost every cause has a specific fix. Learn the language and you’ve turned a confusing frustration into a clear feedback loop.

The best welders are the ones who can look at a bead, know immediately what went wrong, and fix it on the next pass. That’s not talent — it’s pattern recognition built through deliberate observation. And you can build it the same way they did: one bead at a time, eyes open.

NEXT STEP: Ready to put this into practice? Our beginner practice project guide gives you a structured first project specifically designed to develop the fundamentals covered here.