Put on rubber gloves to protect your hands. Unlike chemical paint strippers, washing soda is not harmful to your respiratory system, but it burns skin.
Mix ¾ cup of washing soda with 2 cups of hot water. Stir the two ingredients well to form a thick, doughlike paste. If the paste mixture looks watery, stir in additional washing soda until it is thick enough.
Spread a thick layer of the paste onto the painted item with a trowel. Let the paste sit on the paint for five or six hours, and then scrape off the remaining paint with a wire brush or scraper. Rinse the area with warm water. Let it air-dry for three or four hours.