Cast iron tubs are revered for their durability and classic porcelain-enamel coating. Over time cast iron tubs can, however, fall into disrepair. Two common problems that occur with cast iron tubs are rust and surface nicks. Rust can spread and nicks can lead to rust. Remove rust and nicks to restore the appearance and to prevent further damage. Several companies sell kits for repairing nicks.
Things You'll Need
Mild abrasive cleaner
Porcelain repair filler
Porcelain primer/bonding agent
Porcelain-enamel refinishing paint
Clean the tub's surface by wiping it down with a rag dampened with acetone.
Remove surface rust spots by scrubbing them away with a mild, abrasive cleaner and steel wool.
Remove penetrating rust by scrubbing it away with a solution of half muriatic acid and half water, using a rag. Always add acid to water--not the other way around. Wear long sleeves, acid-proof gloves and safety glasses. Do not let muriatic acid go down the drain. Sprinkle the treated areas with a generous amount of baking soda to neutralize the acid so it can be rinsed. Ventilate the area for the release of gases.
Fill the nicks with porcelain repair filler, using a putty knife. Allow the putty to cure according to the drying time noted in the manufacturer's instructions.
Sand the patched areas smooth with 220-grit sandpaper. Wipe away the residual sanding dust with a damp rag.
Paint the patched areas with a coat of porcelain primer, using a small paintbrush. This may be referred to as bonding agent.
Paint the patched areas with two to three thin coats of porcelain-epoxy refinishing paint. Allow five minutes of drying time between coats. Allow the final coat to fully dry before using the tub.