Acid Etching
This generally is of a hydrofluoric, phosphoric or hydrochloric solution that eats into the surface increasing the surface roughness and micro-porosity to some degree. Care must be taken that the surface does not discolour and cleaning regimes may need to be modified. Ultimately, acid-etching often degrades the surface visually and structurally and during treatment, you cannot allow public access so the premises may have to be closed entirely depending on location and purpose.