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Why Does My Weld Look Porous?

March 2026 | By Dan Johnson

You finish a weld. It looks okay from a distance. But get closer and you see it: tiny holes. Small pits. Like someone poked a bunch of holes in your bead.

That's porosity. And it's the #1 defect beginners face.

What Porosity Actually Is

Porosity is gas pockets that get trapped in the weld metal as it cools and solidifies. The gas can't escape, so it leaves behind tiny cavities.

These holes weaken your weld. They're stress concentrators — the spot where cracks start. An inspector will fail a porous weld every time.

The Real Problem: You Can't Always See It

Here's the tricky part: surface porosity is easy to spot, but subsurface porosity is invisible.

You might run a beautiful-looking bead on top. But underneath, you've got a sponge. You won't know until an X-ray or ultrasonic test fails.

A photo cannot see gas pockets under the surface. DimeVision calls out visible porosity on a bead photo and what to change on the next pass. It is a practice aid, not an inspection.

What Causes Porosity in MIG Welding

1. Contaminated Base Metal

Oil, rust, paint, or dirt on the metal creates gas when heated. Clean your metal. Seriously. Every time.

2. Wet or Old Filler Wire

Filler wire absorbs moisture. Keep it sealed. If it's been sitting out for months, throw it away.

3. Improper Shielding Gas

Not enough gas flow (typically 25-35 CFH for MIG). Too much turbulence. A leak in the hose. Wrong gas mixture.

4. Drafts and Wind

Working near a door or fan? The shielding gas gets blown away before it can protect the weld pool.

5. Going Too Fast

Travel speed that's too fast doesn't give gas time to escape the pool. The result: trapped pockets throughout your bead.

How to Fix It

• Clean the metal. Wire brush or grind to bare metal. No oil, no rust, no paint.
• Check your gas. 25-35 CFH. No leaks. Right mixture (typically 75/25 argon/CO2 for mild steel).
• Store your wire. Keep filler wire sealed dry. Don't use wet or old wire.
• Shield from drafts. Set up a wind screen if you're working near a door or fan.
• Slow down. Give the weld pool time to release gas before it solidifies.
• Check your angle. Too steep an angle can blow gas coverage off the pool.

The AI Advantage

Here's the thing: you might think your weld looks clean, but porosity can hide below the surface.

DimeVision reviews a photo of the bead you can already see. It calls out visible porosity and what to fix on the next pass. It cannot see inside the weld, and it does not decide whether a weld passes.

The Bottom Line

Porosity is preventable. Clean metal. Good gas. Right speed.

And if you're not sure? Snap a photo. Get instant feedback. Fix it before it becomes a problem.

That's how you stop porosity from costing you.