- MIG
- TIG
How to Fill Holes In Your Weld
Sarah Mazlin
13 December 2021
When it comes to filling in holes, there are only really two types of holes you’re going to be faced with. Burn through holes and drilled holes. Both of these holes get filled in the same way (for the most part).
Just like with any welding, your metal should be clean. That includes the inside edge of the hole as well. If it’s a really thin piece of metal, it won’t matter so much, but where possible, run a grinder or sander over it so that it catches the inside and gets rid of anything that might contaminate your weld.
TIG Welding Holes
To fill a hole with TIG, you just dab, dab, dab in a circle around the edge of the hole to start building it up, trying to lead it so that it’s filling the inside edge rather than sitting on top.
It’s like welding on a fillet joint (which is exactly what it is if the hole backs onto another piece). You may need to go around a few times, but once it’s a small enough hole, you can hold your filler rod in the middle and fill in the rest.
The reason you want to go around the circle is to make sure you’re melting into all the edges. If you don’t, you could end up with air pockets in the weld.
Blasting it at the end might cause it to cave in, so as you end the weld, add a bit more filler to make it flush. It’ll only cave in if the backside is open, though.
If it does cave in, once you’ve filled the top side, flip your piece over and run the torch over the backside so the metal properly melts into the edges and there’s no undercut. When you end the weld, move your torch away from the centre, towards one side as you finish.
Now that you’ve finished the weld, go ahead and grind off any metal that protrudes to make it flush. If you’ve got any dips or missed spaces or spots that haven’t been filled properly, go ahead and add another layer of weld to fill it up.
If you add extra filler in, you can push it around with the torch while it’s still liquid and spread it around a bit and get it to ‘wash out’. This is extra helpful on thin metal, especially if you’ve already been blowing through it.
When there’s nothing to back the hole, and it’s not perfectly circle, you want to try and start on a solid or thicker part so you can create a pool and build up the edge. That way, you have a base to start on and can work up to bridging both sides.
If you’ve got an open hole, you can use a copper backer to help hold the weld pool in place. When TIG welding, just clamp the backer into place. The copper won’t stick to your weld, and it’ll keep it from caving in. However, depending on accessibility, it might not always be possible to use one.
MIG Welding Holes
To fill a hole with MIG, it’s the same process as it is with TIG. If you can, use a copper backer. For smaller holes, just a spot weld and it’s filled (with a backer). If it’s a larger hole, build up an edge and go around the hole, filling it in.
It’s best if you do the fill as a series of spot welds, just to keep the heat minimal. If you’re filling in a burn through, keeping your heat input down is best because you don’t want to make it wider.
If you’re using a copper backer, aim your weld at it, especially on thin metal. If you aim your weld at the edge of the metal, it could blow away instead because your settings are too hot and you’ll be left with an even bigger hole. Copper backers are great for MIG welding holes – especially burn throughs – because they’re heat sinks, so they’ll absorb excess heat.
When you use a backing plate, watch the weld doesn’t ‘sugar’ on the backside. Sugaring is most common in pipe welding when the back of the weld isn’t being shielded by gas.
Oxygen and other contaminants affect the weld, and it can look like it’s covered by a layer of sugar. If your weld sugars on the backside, you can take a grinder to it, get rid of the crystals, and weld that side so that the hole is fully filled and contaminant-free on both sides.
If you have a big hole, 1cm or more in diameter, and/or you can’t get to both sides of it, it’ll be easier to plug it. To plug a weld, cut out a circle that’ll fit snug, spot weld it in and grind it flush afterwards.
If the hole you’re filling is on a thicker piece of metal, cut your plug from a thinner piece of metal (around 5mm thinner). That way, you can tack in the plug and have room to fill in either side of the plug with weld metal.
If you’ve only got access to one side of the hole, cut your plug from metal that’s only 2mm-3mm thinner. You can grind everything flush once it’s done. Leaving space to fill with weld is just extra security to make sure your hole is properly sealed, and the plug has been fully melted into the outer edges.
You can plug holes of any size with both MIG and TIG, but it might be less time consuming to fill them with a weld if they’re small.
Filling holes in your weld might take a bit of patience, and sometimes it takes a bit of readjusting your settings if you’re burning through. But, once you’re done, most of the time (with a bit of grinding), you won’t be able to tell there was ever a hole in the first place.
Get The Free Ultimate Welding Guide!
Welding tutorials, tips, and settings in one eBook.