Grouting White Marble with Black (Charcoal) Grout

QUESTION:

I just installed a 12x12 marble (polished) checkerboard (white and black) tile in my laundry room. The wife wants black grout (charcoal). Will this penetrate into the white marble? I used white thinset and plan on using unsanded black grout. I obviously do not want to do this if it will bleed into the white. Any help would be greatly appreciated.

ANSWER:

Contrary to what you often read/hear about marble... it is not very porous and does not stain easy... common misconception that it does.

However, the marble tile edges will be more porous than a polished face and the black grout could bleed and cause some discoloration to the white tiles since it will be in contact with the marble and wet for quite a while before curing.

This can occur when using a darker colored thinset too.

But using a lighter colored grout may not be the answer since it could also bleed into the black tiles making the edges look foggy.

And a light colored grout will show dirt way more than the dark grout.

The most effective way to combat this potential problem is to seal the marble tile edges before applying the grout.

If the tiles are polished, then the face most likely will not need (nor will it take or be able to absorb) a sealer.

Polished marble is nearly non-absorbent and rarely needs sealing. All you need to do though is water test the marble.

The unpolished edges though will be more absorbent and should take a sealer. We suggest using these recommended marble & granite sealers.

You must take care not to let any sealer residue remain or dry on the face (if polished) or it will leave a streaky haze that will require stripping.

You could also simply perform a test with some left over tiles. Set them on a level surface (piece of plywood, etc.) and apply the grout. Let sit for a couple days and see if any absorption/discoloration occurs.