If you like to cook, you have to be on the lookout for grease buildup on your kitchen walls, no matter how well the exhaust fan works. Make the cleanup as painless as possible by doing it often; once the walls start to look dingy, you need a stronger cleaner, and that could mean trouble for the wall finish. It's always best to try mild cleaners before you reach for heavy-duty ones, and you can make powerful grease-cutting solutions with household substances and avoid the need for strong detergents.
Mix a mild grease-cutting cleaning solution by adding an ounce of dish soap to a gallon of warm water. Wipe the greasy spots down with a nonabrasive cellulose sponge, moving the sponge in a circular motion. Work in sections, and wipe each section dry with a cloth before moving on to the next.
Add a cup of white vinegar to the mixture if you need a stronger cleaner. Vinegar is acidic and has the ability to dissolve grease. If it works better, but still not well enough, try adding more vinegar or a cup of ammonia.
Make a paste with baking soda and water. Scrub the greasy spots in corners or along the edges of trim with it, using your sponge. Wash the paste residue off with clean water, and dry the area with a cloth.
Heat a wet sponge in the microwave for about 30 seconds to clean grease off the woodwork. Put some vinegar in a spray bottle and spray it on the grease, and then wipe off the vinegar -- and the grease -- with the sponge. You can use citric-acid based cleaner in lieu of vinegar. Be sure to wear rubber gloves -- the sponge is hot.
Wash walls and woodwork with heavy grease buildup using a mixture of 1/2 cup trisodium phosphate to 1 gallon of water. TSP is a strong detergent, and you should use it only when nothing else works; it dulls the sheen of painted walls and finished woodwork.