Address mold prior to painting a bathroom wall by removing any visible spores, sealing in remaining mold and adding mold-deterring chemicals or fixtures. Because invisible mold spores can spread throughout the room, apply this process throughout the bathroom even if the mold is not visible. Use safety glasses, rubber gloves and a ventilator mask.
Ventilate the area
Ventilate the bathroom as well as possible, either by opening windows or running a functioning and effective bathroom exhaust fan.
Remove fixtures and repair leaks
Take out and wash any removable fixtures, such as towel racks and hooks. Look for and repair any mold-causing leaks.
Mix borax and white vinegar solution
In 2 cups of very warm to hot water, mix together 2 tablespoons of borax and ¼ cup of white vinegar.
Apply borax solution
Scrub or spray all bathroom surfaces, including the ceiling and floors, with the borax and vinegar solution.
Apply a mold-sealing primer
After sanding and preparing the walls, apply a mold-sealing primer to prevent any remaining spores from spreading.
Use an anti-mildew paint
If possible, use an anti-mildew paint on the walls to stop mold from returning. To prevent new growths, install a dehumidifier to prevent condensation and enhance ventilation.