I am learning stick welding and yet to learn how to make smooth welds without crevices.

But I already have quite a few now and wonder what to do with them. I tried to remove the slag inside them with a wire brush and drill bits, but there is always some slag left which seemingly prevents filling them with additional welds: molten steel does not seem to be eager to go in and seal them:

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Currently I have no better idea other than using drill bits to drill the slag out of them one by one, inevitably removing some steel, and trying to weld over again (and, perhaps, again).

Are there some better ideas/techniques?

If I knew for sure that I could just leave them I would happily do so (absolutely no desire to be drowned in perfectionism). But this piece is supposed to be coated with zinc paint (like this one), then with some epoxy primer and be buried in damp clay soil where I hope it will not rot for a few decades at least. These crevicies seem to possibly compromise the quality of coating and I think they could result into defects/holidays which will allow water in and thus ruin the effort. Or maybe not?

(Hot dip galvanising would have been ideal of course but it is not available in my area)

  • 1
    Slag is usually loose/not bonded well to the weld. Should have a welding hammer to bang most of the loose slag off and then use a wire brush. Need to remove the slag if you want put anything on top, more weld or paint.
    – crip659
    May 18, 2022 at 10:06
  • @crip659 Slag hanging on protuberant surfaces is easy indeed. It's the slag inside cavities/crevices that is difficult. It crushes into sand which sticks inside. I've been using vacuum cleaner to suck it out.
    – Greendrake
    May 18, 2022 at 10:14
  • When you are learning to weld, you should spend enough time welding together bits of scrap that are not "a project" to get to the point that you can run a decent bead before you start welding on projects. Weld them together, cut them apart, weld them together some more....
    – Ecnerwal
    May 18, 2022 at 11:05
  • @Ecnerwal That certainly makes sense. However, it also depends on how important a good smooth weld is for the project. Say if I could hot dip galvanise the welded object I would not worry about the inclusions of slag (so long as the weld is still strong enough) as the object will be underground and thus not (dis)pleasing anyone's eye.
    – Greendrake
    May 18, 2022 at 11:15
  • 2
    Ah, but just how weak can it be? Slag inclusions are very much weak spots and the cause (or starting point) of failures in welds, which is why they are forbidden in "real welding"
    – Ecnerwal
    May 18, 2022 at 11:32

2 Answers 2


So grind those holes out and re-weld.

Getting a good fill comes with practice, I found that if I was "pushing" the arc into the molten bubble you get the "wave" effect and keep sufficient material there. I found that moving too fast was the cause - for me anyway.

  • +1 = grind it (all) out and start over. Slag inclusions in the weld is 100% poor technique. Slag should be on the surface of the weld only, and you remove it with a chipping hammer/wire brush. Welding is very much a physical/manual skill that requires practice (and self-teaching is a hard way to get there.) Slag will float to the surface of the molten steel naturally, so you are not maintaining a good puddle if it's trapped in the finished weld.
    – Ecnerwal
    May 18, 2022 at 10:57
  • @Ecnerwal get it right, and the slag peels itself off, no hammering etc needed.
    – Solar Mike
    May 18, 2022 at 11:12
  • That depends on the rod number (and associated flux type.) Some will do that. others won't.
    – Ecnerwal
    May 19, 2022 at 0:05

Grind to remove imperfections as needed. The under cut, with or without slag , may be acceptable depending on the product. Industrial work generally requires X-ray to check the full thickness of the weld. Basically it requires a lot of practice to make good welds.

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