Removing Rust Rings from Cast Iron?

Once rust starts on a cast iron tabletop, is it too late to stop it?

Could someone tell me how to clean rust and rings left by someone leaving glass on my table saw? It made a real mess and no one is admitting they did it. The rust is my fault. - Bob Bean

Rob Johnstone: As Neil Young says, rust never sleeps...but it can be prevented. Sadly, once a cast-iron top has been rusted, it will never look as it did before. You can get rid of the rust and smooth the surface, but some discoloration will remain. I attack it with WD40® and ultra-fine steel wool, and follow that with paste wax. That is the old school method, but there are some really great products that are more effective in dealing with the problem.

A good coat of cast-iron conditioning product and a layer of paste wax will do a lot to prevent rust from starting, but the number of cast-iron machine tops that I've seen without discoloration from rust is very small. Cast iron is tough and durable, but someday, somehow, it will get wet and rust.

Tim Inman: There is a pleasure in having and using a perfect, bright, shiny table top on our tools. It is often, sadly, a short-lived one. Those stains can be very very difficult to remove. A simple sanding with very fine wet-or-dry sandpaper (400- or 600-grit) will remove the roughness. A good paste waxing rubbed in with #0000 steel wool will make it slick again. But the chances are that you'll always be able to see that visual blemish. That said, I have many antique tools in my shop that aren's so much "lookers" as they are great to use. My late 1800s Crescent brand jointer is one example. It was salvaged from the Beloit Wagon Works factory, in Beloit, Wisconsin in the early 1980s. It had been relegated to a leaky storeroom and was just one huge rust bucket when I found it. It is now polished, painted, and fully functional - but the top shows the rust stains to this day. It also shows the hand scraper marks where the original top had been HAND worked flat and true; something no new tool in a wood worker's shop would show today. I wouldn't trade it for a shiny brand-new one, ever.

Chris Marshall:  We've got a big pond behind our home. When we first moved in, my shop was just a a dirt-floor pole barn, so it took some time to get that up and running. In the meantime, my cast-iron tools sat in the garage, and damp air from that pond turned those pristine tool tables a light brown in no time. After the anguish passed — I really like the bright, shiny top that Tim mentions — I bought a pump spray bottle of a product called Rust Free made by Boeshield. A few spritzes of the spray, and the rust wiped right off with a rag. The initial shine of my cast iron was diminished, and it's never been fully restored since, but the surfaces are easy to clean whenever I get a spot of sweat or some dampness on a cast table top. I chalk the gray discoloration up to "character." Sort of along the same lines as those dings and nicks on a well-loved piece of family furniture. You just need a good way to erase rust and then take it in stride.