The method for repairing damaged porcelain on steel tubs depends on the extent of the damage. Apply a porcelain touch-up kit for minor surface scratches. If you have gouges or deep holes in your tube, you'll have to prepare the surface and use a filler or epoxy to replace the missing porcelain. Use a dust sheet to protect your tub and protective goggles or glasses for your eyes.
Mix equal parts of hardener and catalyst in the mixing cup. Stir using the provided stick.
Apply one coat and allow it to dry for about 30 minutes.
Apply a second coat and let it dry for the same amount of time. Two or three coats should provide a nice, shiny coat of porcelain.
Sand down the affected area by starting with 220-grit sandpaper to remove any loose porcelain flakes. Repeat the sanding process, each time using a finer grade sandpaper, until you reach 800-grit or 1000-grit. Sanding the damaged area in layers removes all of the imperfections.
Vacuum the loose debris and rub the immediate area with acetone, using a rag.
Fill the gouge with water putty--a waterproof filler--if the gouge is more than 3/8-inch deep. Apply the water putty with a plastic spreader and let it dry for several hours.
Apply the porcelain repair kit hardener and catalyst (see Touch-Up Kit section above).
Mix equal parts of epoxy activator and hardener, using the provided bowl and mixing stick.
Fill the holes with the epoxy mixture. The epoxy forms a strong base, replacing sections of missing porcelain. Let the epoxy dry for 48 to 72 hours.
Repeat the sanding process as described in the Porcelain Repair section.
Finish the job by using the porcelain repair kit from above. You may need more than one kit, depending on the size of the damage.