• Apply a drop of muriatic acid (swimming pool acid) to the underside of the material. The underside won't matter if it etches and is less likely to have a sealer on it that interferes with the test.
• If the drop fizzes, the material can be acid etched.

Still picture of acid fizzing on travertine limestone Video of acid fizzing on concrete

If your material is acid sensitive:

1. See Aldon "Grout Easy" before grouting to eliminate the need to clean grout residue with an acidic cleaner.
2. If it is too late and you have stains from the grouting process - test with Aldon "Grout Restoration" at highly diluted strength.

For other cleaning and stain removal - use only Aldon "Insta-Clean". It is non-acidic and will not cause damage, but test first.