Field Repairs for a Cast Iron Radiator

Scott Gibson

Editor's Note: See Scott Gibson's follow-up to this article, Radiator Repair Won't Hold Water - Replace it.

We just finished renovating an old house full of radiators. My husband spent many hours restoring the radiators to their full beauty. Getting our heat turned on has been the last thing we've been waiting for after two years of work. The men who were getting the heat turned on discovered a leak in the bottom of one of the cast iron radiator fins. How can we fix the leak? It's the only thing keeping us from turning on the heat. It's getting cold and we're out of money!

This note came from a woman in Washington, D.C., and my first thought was the leaky fin could be removed and repaired, or simply removed and the radiator put back together with one less fin.

cast iron radiator

That should be straightforward, but it would require that the plumber drain the radiator, pull it apart, and reassemble it when the repair was complete. Old radiators can be stubborn, and the labor would have been an unwelcome expense at the end of a two-year project that no doubt cost more than the couple anticipated.

And then there's that delay while all this goes on.

Which leads us to JB Weld, a brand of epoxy revered by shade tree mechanics and desperate do-it-yourselfers since the late 1960s.

Sam Bonham developed JB Weld in his Texas machine shop, and later went on the road with his wife Mary to sell it to auto parts stores. Sam has passed away, but JB Weld is still produced by the family owned company he started.

Like other epoxies, JB Weld is a two-part adhesive that consists of a resin and a hardener. But this one, when cured, behaves more or less like metal. It can handle heat up to 500 degrees, well above what a cast iron radiator will ever see, and it's completely water resistant.

It sticks tenaciously to metal. The only way to get it off is mechanically--with a grinder or file--or by heating it to more than 600 degrees.

Surface preparation is key. The area to be patched can't be wet, and should be cleaned with acetone or lacquer thinner. Anything that would leave a petroleum-based residue behind won't work.

On paper, it sounds like JB Weld is perfectly suited for patching a small leak in a radiator.

The leak here wasn't serious, producing a few drops of water every half-minute or so. The couple's contractor drained the water out of the radiator and planned to use a marine epoxy followed by JB Weld to stop the drip.

Last we heard, the repair was holding and the leak had stopped.

Using epoxy instead of disassembling the radiator may not be a perfect solution. But that's sometimes the nature of fixing old things. Expediency does have its place, and if you don't think your forebears would have taken any short cuts when they had to, take a closer look at your old house.

You'll probably find evidence they did.

If this small drip isn't completely solved not much has been lost. A more complete repair can wait until the weather, and finances, allow. And if it's a permanent fix? So much the better.


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