White Marble Tiles Turning Gray In Shower

by Barb
(Dexter, MI)

QUESTION:

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.


ANSWER:

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, marble
does not 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.

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Water Stain in Marble and Granite Tiles
by: Anonymous

I had a water leak from a pipe in my bathroom wall, and now a small part of my marble floor and granite floor in the hallway outside the bathroom have stains.

I discovered the leak yesterday by seeing the discoloration in the tiles.

Will both go back to normal as the tiles dry out, or can the stains become permanent?

==== Countertop Specialty comment:

Maybe. If the water was relatively clean (not rusty or dirty) then it may simply evaporate and leave no trace or stains.

I'd guess this is a long shot and it will likely leave some evidence. Floods and leaks usually do.

A few things could happen:

1 - You could get some efflorescence (minerals from the water coming out of the tiles like a chalky crust). This will eventually all come out. Just need to sweep away usually. Or may need to use a Hard Water Remover for natural stone.

2 - You could get rust stains either from the water or if you have white marble, then iron deposits inside the marble can oxidize in a flood creating rusty stains.

But this generally only occurs with white marble like Carrara. Other colors of marble don't carry iron deposits.

If it does occur, then replacing the tile is the only option.

You could lighten the rust stains some, but they typically are impossible to completely remove when from flooding (vs. metal object rusting on the surface).

3 - General discoloration or grayness from dirty water.

Same as number 2. You can try using a Marble Stain Remover but with flooding the stain is often full thickness and difficult to eliminate. It may lighten though.

4 - The water evaporates and doesn't leave any stain.

I'd use fans to try and dry it out as fast as possible and prevent further spreading. Then wait several days... maybe a week and see what happens.

If after two weeks and it's good and dry and you still have stains, then try a stain remover and hope for the best.

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