I also buy an expensive car and don’t drive it through the 0815 car wash... You remove the top coating of the stones with the high-pressure cleaner. As a result, the stone absorbs dirt, verdigris, etc., which you will never get out again. It’s the same with tiles and grout. If you clean it with chemical weapons like Bref, Cillit Bang, etc., the top coating dissolves and mold, discoloration from shower gel, shampoo, etc., settles more easily.