White Marble Tiles Turning Gray In Shower
We installed sealed, white marble in our walk-in shower on the floor and walls. The bottom 1 1/2 rows of tiles on 2 walls are turning gray. We don't know what is causing this. If it was where the water was hitting it, I would think the floor and more of the wall tiles would be gray also.
The problem is most likely a bad installation and/or cracks or voids in the grout allowing water to get trapped behind the tiles where it cannot evaporate.
Instead it just absorbs into the marble. Wet stone is always darker in color, so the white marble tiles become gray and stay gray since they are saturated with water. And the fact
that you applied a sealer is complicating the issue by making it even harder for the water to evaporate through the outer marble tile surface.
The sealer prevents absorption into the stone, but it can also prevent water from evaporating out of the stone especially when the tile is on a floor or wall. This is the textbook reason
why applying a sealer to stone in a wet environment like a shower is not recommended.
Sealers help prevent staining. Very very small risk of staining in a shower and stains are generally easy to remove and rarely permanent. Sealing is a benefit in areas like a kitchen or bathroom countertop or floor that is at much higher risk of staining. Also
stain easy. It etches easily, which people confuse with staining. Thus the commonly stated, but completely incorrect myth that "marble stains easy". And you are not sealing
against the water, so sealing a shower provides almost no benefit, but may complicate just such a problem as you describe.
Water will not stain and unless there is a bad install or grout cracks any water that does absorb into the tile quickly evaporates between uses... no problems.
Since marble is rather dense with low absorption it takes prolonged contact with water for it to absorb.
The problem is localized because it is relative to where water is entering. The bottom tiles on the wall are going to be exposed to plenty of water even if it isn't where the water stream hits. Test this
by discontinuing use of the shower for 4-5 days, maybe a week to let the shower completely dry out. You should notice the gray tiles become white again as the water evaporates.
Check for and repair any cracks in the grout. Pay particular attention to the wall/floor seam, which is a common problem area. If you find no grout damage
, then you may have a bad installation. Bad install means rip out and re-do (at least the affected area). It may also be possible
that you have a pipe leak causing the problem, but you should start by drying out the shower and proceed from there to find the cause.