QUESTIONI 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?
ANSWERANSWER - 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