In this video, This Old House plumbing and heating expert Richard Trethewey shows how to save an old, but elegant, cast-iron bathtub.
1. If the outside of the tub has been painted, use a paintbrush to apply a thick coat of paint stripper to the surface.
2. Once the stripper has softened the paint, scrape off the paint and stripper using a 3-inch-wide putty knife.
3. While wearing a dual-cartridge respirator, brush a thin coat of hydrofluoric acid over the entire interior of the tub. The acid will etch the surface, ensuring a good bond with the new epoxy finish.
4. While waiting for the acid to etch the tub, use small files, dental picks and sandpaper to clean all paint and grime from the tub's claw feet.
5. About 30 minutes after applying the hydrofluoric acid, scrub clean the interior of the tub with lots of water and paper towels.
6. Repair chipped enamel by first using a rotary tool fitted with a grinding stone to grind away any black carbon stains and to rough up the enamel around the perimeter of the damaged area.
7. Wipe the repair clean of all dust, and then fill the chipped area with auto-body filler.
8. Allow the filler to harden, then sand it smooth with 220-grit sandpaper, followed by 320-grit sandpaper.
9. Use a high-velocity, low-pressure (HVLP) paint sprayer to apply three coats of epoxy primer to the interior and exterior surfaces of the tub. Wait for the primer to dry completely before proceeding.
10. Use the HVLP sprayer to apply an epoxy topcoat to the interior and exterior of the tub. Allow the epoxy to fully cure before moving the tub or installing the faucet, spout and other hardware.