If your let graffiti or spilled spray paint sit on a surface for too long, it can soak deep into the wood where it will be almost impossible to remove. Prevent this by removing the spray paint as soon as possible. Use a homemade spray paint remover if you are concerned about introducing strong chemicals into the environment.
Pour 1 cup of borax into a bucket.
Add 1 cup of ammonia.
Add 1 cup of washing soda. Be aware that washing soda is different from baking soda. Washing soda is sodium carbonate, while baking soda is sodium bicarbonate.
Add 2 cups of water to the bucket, and mix until all the ingredients are thoroughly combined.
Brush the solution over the spray paint. Leave it alone for 10 minutes.
Scrub the area with a scrubbing brush until you've removed all the spray paint.