Welding a Cast Iron Bird Bath Back Together

A friend of mine gave me this little cast iron birdbath to fix after hearing that I got a welder. I've never tried to weld cast iron before, and I know that it has its peculiarities due to the metallurgy. Since the thing is already broken, and taking it to a professional to fix wouldn't really be worth the money, I'm going to attempt to fix it myself.

I did a bit of research online before starting the project, and identified a few key things. First, the metal needs to be clean before welding to avoid contaminants in the connection. This means grinding back to bare metal, and then cleaning with acetone to remove any particles.

Second, because cast iron has minimal ductility, preheat is important. If you introduce a lot of heat in a small area, such as what happens with welding, and then let the piece cool, cracking is very likely. Instead, a large area of the piece should be heated with a torch, and then the area in the weld zone should be heated to somewhere between 200°F and 750°F (100°C to 400°C). After welding, the piece should be cooled slowly to mitigate cracking.

I tried to clamp this together, but it's really squirrely and wasn't happening. So, using some welding magnets, I propped it up as best I could so that the parts mated.

I used a MAPP torch to preheat the stem of the birdbath, being sure to also heat the area around it.

With the thing preheated, time to stick it back together. I went for relatively minimal welds here to keep the heat input as low as possible.

After welding, I let it slowly cool, being sure to hit it with a torch every once in a while so that it didn't cool too rapidly. After the piece cooled (and happily, with no cracking), I ground off the blobby welds to make it look a bit more presentable.

To try and match the weathered patina of the birdbath, I used some rust activator I had from another project. This solution causes bare iron or steel to flash rust pretty quickly, and then over time and wet/dry cycles outside hopefully the repaired area will match again.

Luckily, it looks like I was able to salvage this broken birdbath for my friend and keep this cute little piece from being scrap.

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