Why did the black grout stain my tile?


I 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!


ANSWER - 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.

4 thoughts on “Why did the black grout stain my tile?

  1. EA Canning says:

    Hello, a bathroom install completed this week and yesterday noticed several of the porcelain tiles from Maravilla are turning brown around the edges. Grout is light grey and contractor said used a white thin set/. I’m so upset.

    • Donato Pompo says:

      Technically porcelain tiles are impervious that typically has an absorption rate of less than 0.1%. So it is unlikely it is absorbing a stain. If it is a glazed porcelain tile the glaze is also impervious, but sometimes they have micro fractures called crazing. Some manufactures do this intentionally to give a distressed look, but sometimes it happens unintentionally.

      If the glaze has fractures, then when tile is grouted the grout pigment can get imbedded into the fracture and it can be difficult to remove. That is why grout manufacturers always say use a grout release (sealer) prior to grouting when grouting with a contrasting color grout.

      In terms of removing it, first you need to determine if it is trapped pigment. If so sometimes a slightly acidic tile cleaning solution with a brush will remove it. You can try using a stone poultice to draw it out. Whatever you do it is trial and error. You have to test out the method before applying it to the entire application to make sure you will be satisfied with the outcome.

  2. Albert Fernandez says:

    I tested some glazed porcelain tiles for lead using testing swabs with sodium rhodizonate, which are supposed to change color if there is lead in the glaze. The swabs did not change color but purple showed up on the tile glaze itself. Does this mean that the glaze does contain lead? If you don’t know, could you refer me to someone who would? Many thanks.

    • Donato Pompo says:

      Whether your test protocol was performed was valid or not according to the appropriate ASTM test protocol, would have to be determined in order to determine the validity and meaning of your rest results. You should search for an Industrial Hygienist in your area to have them evaluate your findings.

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