Made from clay and other natural materials fired to form a hard, stable product, bricks are porous, which makes them susceptible to stains from food, mold or even the errant permanent marker. To remove permanent marker stains, start with basic household cleaning products. If those don't work, though, consider using a power washer set at a very low setting. Angle the stream of water across the bricks, rather than straight at them, so you don't cause damage.
Dish Soap and Baking Soda
Mix dish detergent, baking soda or pumice, ammonia and enough hot water to make a thick paste. Brush it on the stains with a scrub brush.
Wait 10 to 20 minutes until the paste is dry. Scrub the area vigorously with a scrub brush.
Wipe the paste off with a paper towel and rinse it with clean water. Dry with a dry paper towel.
Mix 1/2 cup trisodium phosphate with 1 gallon hot water in a bucket.
Dip a scrub brush in the solution and vigorously scrub the stains.
Rinse with clean water and dry.
Mix 1/2 cup chlorine bleach with 1 qt. of hot water in a bucket.
Dip the scrub brush in the solution and soak the stain with it. Wait 10 to 20 minutes.
Rinse the area with clean water and dry.