Tips For Rust Management

No woodworker who takes pride in his tools wants to see them discolored or damaged by rust, but the battle against this red devil can be a never-ending one. This is especially true for anyone living in oceanfront areas or in regions with big fluctuations in humidity and temperature levels throughout the year.

Short of moving to southern Arizona, most of us have to take preventive measures occasionally to keep rust at bay. For hand tools such as chisels or plane irons, the issue is more a cosmetic one because regular honing or grinding of the cutting edge keeps the business end of the tool in good shape. The idle portion of the blades can be sprayed with lacquer or clear polyurethane, or wiped down with a light machine oil.

The cast iron surfaces of machinery present a bigger challenge because they can’t be wrapped or stored in cases or drawers. They also have much more thermal mass than a small hand tool and so can attract much more moisture condensate. More on this later.

Certain conditions, such as having your shop in a damp basement or an unheated garage, are an invitation to rust. But not all of us have options for relocating our woodworking tools, and in those situations we have to use a mix of strategies:

• If you are uncrating a new machine with cast iron tables, it may have oil-soaked paper stuck to the table, or a brown gelled grease. Use mineral spirits and acetone to dissolve the grease, and wipe repeatedly until no residue is visible. Then either place the machine in sunlight or use a heat lamp to warm up the surface; grease residue will continue to “sweat” from the surface for a short period and it must also be cleaned off with solvents.

• Next, apply a protective layer to the exposed surfaces. Paste wax is a traditional and reasonably effective option, but don’t use automotive waxes containing water or oily additives. These are really for painted surfaces, and they can transfer residue onto workpieces and cause finishing problems later. There are industrial sealants designed specifically for rust prevention on steel and cast iron surfaces. These are designed to seal the surface and dry-cure rather than leave an oil residue the way machine oil or a product like WD-40 might do. Avoid sealers that contain silicone, as they too can leave residues on wood surfaces and interfere with glues and finishes.

• If the cast iron surfaces already have some light rust or oxidation, use fine steel wool, a scrubbing pad, or a rubber abrasive block to remove it. Regular maintenance to remove light rust is critical; if left unchecked, heavy rust will cause a blistering effect on the surface as the large iron oxide molecules displace the smaller iron molecules; if this has already happened, regrinding the table is often the only way to remove the damaged portion of the surface.

• Try to control the shop climate. In basements, run a de-humidifier to remove excess moisture vapor from the air. In garages, try to keep the space heated so the cast iron tables don’t become large thermal sinks that will stay cold for days or weeks after the weather begins to warm up. Spring warming typically brings more humidity, which will condense on the cold machine surfaces and promote rust. If you can’t heat the entire garage effectively, try storing your machines together in one corner and using a small ceiling- or wall-mounted electric infrared heater to keep the tables warmer. Infrared heat warms objects, not the air, so the tables will capture and hold the heat. This is a relatively inexpensive rust-preventive measure and has the added benefit of allowing you to use your shop in colder weather.

• Finally, don’t let moisture sit on the surfaces. This means don’t place a cold drink on your table saw and let it drip condensation onto the cast iron. Also, your own sweat will accelerate rusting in spots, because of the salt content in perspiration. Wipe sweat drops up promptly, and re-apply table sealants on a monthly basis to ensure good protection.