One of my steam radiators has a small leak under the bottom. No hole is visible, but water drips out at a rate of a few drops per minute. Various websites suggest applying a 1 mm thick layer of J-B Weld after sanding and cleaning with acetone.
Does the fact that the radiator leaks necessarily mean that it is completely rusted from the inside and that leaks will soon appear elsewhere? Or is it likely that a slow leak is not due to rust, or that the rust is in only one place?
The radiator is decades old (perhaps even a century), but has been moved recently in order to repair the floor. The leak is clearly away from the valve.
Best Answer
I haven't had very good luck with repairing steam radiator patches from the outside (sample size: 2). Steam under pressure is very good at finding microscopic holes between patch and substrate, and enlarging them.
What I have done successfully is an inside patch with epoxy, using a wire brush and steel wool to prep the surface. Getting at the leak may be a challenge, particularly with a radiator that has more than 4 sections you may need to break the sections apart (if you do, this is an excellent time to get the exterior sandblasted and painted).
Simplest and most cost-effective solution is probably to find an architectural salvage shop and replace the radiator (they might take your old radiator as a partial trade).