Cleaning up: grinding, wire brushing, and spatter
Alright. So we've done the ground clamp, we've done wire, we've done matching settings, gas flow, standing at the table, striking the arc, pace, running a bead, and reading whether it's good or cold or burned through. Now you've got a weld sitting there and it looks... fine, I guess, but also kind of crusty, and you're wondering what you're supposed to do with it. This is that lesson.
First, what's actually on there
Every MIG weld comes out of the hood with some stuff stuck to it that isn't part of the weld itself.
- Spatter. Little balls of metal that flung off while you were welding and stuck to the surrounding metal. Sometimes right next to the bead, sometimes a couple inches away. Cold welds throw more spatter, in my experience, so if you've got a lot of it, go back and check your settings too.
- Slag-like crust or discoloration. MIG doesn't produce slag the way stick welding does, but you'll still get some soot and a dark oxide film around the bead, especially if your gas coverage wasn't great.
- The bead itself might have sharp little peaks or a ridge along the edge where it meets the base metal, which can be sharp enough to catch a finger if you're not careful.
None of this means your weld is bad. It's just what welding looks like before you clean it. I feel like new people see all that crust and assume they failed, and mostly they didn't, they just haven't gotten to this step yet.
Wire brushing
Start here, it's the gentlest option. Get a wire brush, and I'd get a dedicated one for steel and never use it on aluminum or stainless if you ever branch into that, cross-contamination is a real thing people warn you about for a reason even though I couldn't tell you the chemistry of why.
Brush along the bead, not across it, with some real pressure. You're knocking off soot and light spatter and the loose oxide film. You'll see the actual metal color come through underneath, usually a cleaner gray or silver depending on your metal. If it's still dark and crusty after a good brushing, that's a clue your gas flow or technique needs another look, not a clue to brush harder.
Wire brushes throw off tiny bits of wire bristle sometimes. Safety glasses stay on for this too, not just for welding. People forget that part.
Grinding
For spatter that's really stuck on, or for a bead you want smoothed down flush, you'll want an angle grinder with a flap disc or a grinding wheel.
A few things I've learned, some the hard way:
- Light passes, not one big gouge. You're not trying to remove metal, you're trying to clean the surface. Let the disc do the work.
- Watch your angle. Too steep and you'll dig a groove into the base metal around your weld, which weakens things and looks bad besides.
- Sparks go everywhere. Way more than welding sparks, and they travel further. Clear your bench, know where they're landing, and keep anything flammable well out of the way. I do this outside or in the corner by the vent fan Jan made me set up, never in a closed-up space.
- Gloves and a face shield, not just safety glasses, if you're grinding for real. Cutting discs and grinding wheels can grab and kick, and a stray spark down the collar is no fun either.
You don't need to grind every weld smooth. Honestly for practice beads on scrap, I usually just wire brush and call it good. Grinding's more for when a weld's going into something you'll actually look at or handle a lot, like a bracket or a cart.
Checking what you've got underneath
Once it's cleaned up, look at it again in good light. This is where you actually get to see your work, and it's kind of the payoff moment, if I'm honest.
I still remember the first time I got a bead that actually looked like the videos, like stacked dimes going down the whole length of it, even and consistent. I brushed it off in the garage and just stood there looking at it for a second because I genuinely wasn't sure it was mine. Then I hollered for Jan to come out and look. She came out, looked at it, said "that looks nice," and went back inside, and I was thrilled the rest of the day over one sentence about one weld. That's how big a deal it feels like when you finally see it clean and it's actually good.
That's the thing about this cleanup step nobody tells you: you don't really know what you welded until you clean it. The dirty version hides a lot, good and bad both.
Before next time
Take one of your practice beads from last time, wire brush it, and look at it in good light. See something you didn't expect, good or bad? Bring it up, I want to hear about it.