Why did the porcelain tile under my rugs turn dark?


I installed rectified Spanish porcelain tile in late 2014 on the entire first floor of my condo. Both the dining room and living room have area rugs with separate non-slip padding underneath. Lo-and-behold when I removed the area rug recently I realized that the covered area is now much darker than the rest. Same on the other area rug. Not sure if the rest of the tile has faded or as I was told by someone, the humidity under the area rug and non-slip pad has turned the tile darker. Have you ever heard of something like this, or is it even possible?


ANSWER - Porcelain tile is not known to fade.  It is not uncommon to find that the tile color under rugs that have been in place a long time are a different color or shade.  Normally it is that the tiles under the rugs are clean and the tiles outside of the rugs are not.  Normally the tiles under the rugs would be a lighter color and not darker.

Porcelain tiles are impervious so they can't significantly absorb, so I doubt that it has to do with moisture.  Although you can get a moisture meter and test the moisture conditions.  Normally the tiles under a rug will tend to have a higher moisture level to a degree, but it should not be extreme.

It could be that the rug padding could have stained the tiles.  Although porcelain tiles are impervious they do have microscopic pores that can trap stains.  Or perhaps if the tile has been subjected to acid washing that could possibly etch the tile and give it a different appearance.

You will need to experiment and trouble shoot through trial and error to understand what has caused these conditions and then to determine how best to remediate it.  Do a deep cleaning of both tiles that were under the rug and those not under rugs.  See what the differences are .  Do moisture testing.  You should be able to


2 thoughts on “Why did the porcelain tile under my rugs turn dark?

  1. R. Mistretta says:

    I am not a business, but I am desperate for help as no one seems to know the problem I am having with my ceramic tile in my home. Somehow moisture is getting under my ceramic tile causing brown and gray stains. I live in Louisiana and it is mostly damp and wet. In heavy rain depending on the direction it is coming, I will sometimes see a gray color on my tile by my front door and windows, that eventually dries out, but I think there is another issue in this room where I have the dark brown stains that do not go away. I have consulted with numerous contractors over the years. Changed the windows, replaced stucco, landscape, waterproofed, gutters all to no avail. I had a foundation company come out and he said where the brown stains are the house is a little lower there, so that could be part of the problem. He suggested redoing the landscape with drainage. I have consulted with several landscape companies, but they all have a different opinion on how to solve it. There is also a musty smell in the room when we have damp and rainy weather. Once the weather improves the smell disappear. I am at wits end on what to do and cannot afford to spend any more thousands to come back with the same problem I had before. I hope you can help me. Thank you for your time.

    • Donato Pompo says:

      I understand that you have a ceramic tile floor that has brown and gray stains. You say that the gray stains come and go with the rainy weather and the brown stains stay. You would like to consider retaining our services as 3rd party impartial experts to evaluate the tile installation to determine the cause of the staining and to determine how best to remediate the problem.

      Louisiana is known for having high water tables. As it rains the water table will rise. If a vapor retarder wasn’t installed under the concrete slab properly water can migrate into the concrete slab and up to the tile and evaporate into the interior area. The water can cause tiles to darken and sometimes it can carry stains that can migrate up into the tile or through the grout joints. This can give the musky smell.

      To stop the moisture migration you need to determine the source of the moisture and whether you can stop it. If you have a high water table or water is migrating laterally from around the outside perimeter of the house you can install trench drains around the perimeter of the house to try to divert the water to drain away. If you can stop the moisture you can stone the staining and smells.

      Before the tile was installed the concrete slab should have been checked for relative humidity to determine if there is a potential moisture problem. If there was high moisture a moisture mitigation system could have been installed over the concrete slab that the tile then can be installed on to it.

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