Milk splashes may go unnoticed for a long time, particularly on white walls. Once the milk dries, it leaves a tough, sour-smelling stain that can't be removed with a simple wiping. You can soften and pick up dried milk with a bit of persistence and normal household cleaning products.
Gently scrape off as much as the stain as possible, using a butter or putty knife.
Mix 1 quart cold water and 1/4 teaspoon liquid dish soap in a bucket or large bowl to make a sudsy solution. Do not use warm or hot water, as this will cook the proteins in the milk, causing it to coagulate.
Dampen a washcloth with the solution and blot it onto the stain.
Spray warm water on the stained area and blot dry with a clean washcloth.
Continue washing, rinsing and drying the area until the milk stain disappears. If the stain won't budge, switch to an ammonia solution.
Dilute 1 part ammonia with 10 parts water in a bucket. Blot the stain with the ammonia solution using a washcloth.
Spray warm water on the stained area and blot it dry with a clean washcloth. Continue washing, rinsing and drying the area until the milk stain disappears. If the stain won't budge, replace the ammonia solution with a 3 percent hydrogen peroxide solution or 1 part chlorine bleach diluted with 10 parts water and continue the cleaning, rinsing and drying process.