Hi All, sorry to hijack this thread. Need so kind advice from the Guru and experts. My frd contractor forgot to instruct his guy to apply BLACK cement for the gap between the mosiac. His 2 toilet wall 50% is already applied with the white cement. Any way to acid wash alway the white cement so that they can reapply the black cement? Have done some googling and found that muriatic acid may help. Do you guys have any solution? Many Thanks. Regards