QUESTIONI just had porcelain tile (Montalcino Crescendo White) with a charcoal grout. All of the tiles appear to have damp pinholes which are now filled with the charcoal grout. I have tried vinegar, but it is not working. Contractor said he has never seen this before and the tiles are defective and will need to completely redo all of the work. Please advise!
ANSWERANSWER - Some glazed tiles have micro fracturing or even pin holes from off-gassing during the manufacturing process. It is always recommended to use a grout release to protect the tile from staining before you grout. The stain is normally caused from the color pigment of the grout. A grout release use to be type of sealer that could be washed off the tile surface during the grout cleaning process. Sometimes sealers are used as the grout release.
Some tiles intentionally have this crazing or crackled finish. It isn't normal to have pin holes in the glaze that you can see. There can be microscopic pin holes that you can't see.
Don't use vinegar or any acidic material or it can make it worst. I would try using a floor cleaning detergent added to water and soaking it in for 10 minutes or so. Then get a scrub brush on an extended handle to scrub the tile surface. Afterwards use a wet vacuum to pick up the dirty water. The rinse the floor with clean water and pick that up with the wet vacuum. Experiment first to see if this will give satisfactory results or not.