Applying a Clear Coat to a Refurbished Cast Iron Radiator

I just had my steam radiators sandblasted. Question one: Do I have to paint them? If I do, is there a clear color paint to keep the beauty of the old radiator? Do you spray or brush on the finish? I want the radiators to stay as bare as possible because sandblasting wasn't cheap and I don't want to ever move these radiators again!

Thanks for your guide about painting radiators. I'm ready to strip and paint mine, which must be 100 years old, but I just want them to be natural (no color). I'm sure the metal has to be coated with something to prevent corrosion, right? Is this possible? If so, what should I use?

Of all the things that plague owners of old houses, refurbishing and refinishing cast iron radiators is right at the top of the list. No single issue surfaces here as frequently, and in fact these two queries arrived within a few days of each other.

Radiators need some kind of finish, not only to protect them from corrosion but also to make them easier clean. And the short answer is yes, cast iron radiators can be clear-coated once the old finish has been removed.

But let's start with a couple of finishes you should avoid: polyurethane wood finishes and at least some high-temperature coatings meant for auto parts and wood stoves.

Minwax makes a line of solvent- and water-based clear finishes that work beautifully on furniture, casework, and trim. As tempted as you might be to try them on your cast iron radiator, don't. The company says heat from the radiator discolors the coating, and because the finish is hard it may crack as the cast iron expands with heat.

Next, I called a manufacturer of high-temperature coatings used on auto engines, transmissions, diesel exhaust systmes, steam pipes, boilers, wood stoves, and barbeque grills. Clear coatings are available in aerosol cans. Perfect, right? Well, no. There's a catch. It won't cure properly in temperatures under 350 degrees F.

Hot-water radiators are unlikely to get much warmer than 180 degrees. Steam radiators get hotter than that, but nowhere near 350 degrees. So unless you can get the radiator into an oven once it's been coated, this finish won't work either.

I did, however, come across a company that strips radiators chemically before sealing them with clear lacquer. Bob Reed, the owner of the Stripping Workshop in Washington, D.C., says his techniques grew out of trial and error, and while the process is possible it's not simple.

After they are stripped of old paint, radiators are cleaned with wire brushes spinning on a flexible shaft. Then they're prepped with a separate chemical treatment and sprayed with pre-catalyzed lacquer. Any trace of corrosion remaining on the metal prevents the finish from adhering properly, Reed says.

Lacquers are extremely fast-drying finishes that should be applied with spray equipment in a properly equipped shop by people who know what they're doing. Most lacquers dry too quickly to be applied by brush, and the atomized finish is explosively flammable as it's applied.

So if you're really after a clear-coat finish for an old radiator, get it to a shop that offers this service and let them work their magic. This just isn't a good home handyman project. You have too much invested in removal, stripping, and re-installation to take a chance on botching the job.