Here in Pa oxalic acid will remove the stain from red clay. Most likely will work for you. First remove the "physical" clay,...Then mix 8 OZ. granular ox per gallon and apply with pump sprayer. It will disappear and then rinse.
Jeff
Half in half muratic let dwell on the brick 2 minutes rinse go home lol.Aluminum brighter on the door or f9 will come right off we see that here all the time.Tell them to put straw down or you will be back in 6 months.