Grout in calcutta gold herringbone shower floor showing rust

[Panama]

The grout in my new shower floor (calcutta gold herringbone) is turning a rust color and pitting. So much of the grout is pitting and showing cracks. The marble is not showing any rust, just the grout. Suggestions? It has only been in 3-4 months. NO chemicals are used for cleaning and a squeegee is used after each shower.

[Tool Guy - Kg]

Welcome to the forum, Panama!

Couple things going through my mind. But let's start with:

Do you have any idea if the tile was set with a material that came pre-mixed and ready-to-use right out of a bucket? Or if a powder was mixed with water or a milky liquid to make the mortar in batches, as batches?

[Panama]

It was a powder mix for sure. Sand-free laticrete since it was applied with with the marble floor.

[fhueston]

this is a common problem with white marble. They contain iron and when exposed to moisture the iron starts to oxidize. I see it all the time.

[Panama]

The marble in the herringbone floor has not turned colors, the grout has turned rusty and the grout has pitted so bad.

[Kman]

Do you know the manufacturer of the grout, and the color?

[cx]

Don't know the color, but from post #3 it's " Sand-free laticrete" grout, Kevin.

I'm curious to know how wide are the grout joints. Can't really tell what size those tiles might be without any perspective in the photos.

[Kman]

I thought he was referring to the setting material, since that's what Bubba was asking about, but you're probably right.

[Flyingscot]

Maybe I'm crazy but that looks like pink mold to me. We have it in my region. I'm also seeing what looks like mildew in the caulk.

[cx]

Yeah, you could be right, Kevin, but looks like she ain't comin' back to tell us one way or the other.

Does Laticrete have an un-sanded thinset mortar these days?

[Tool Guy - Kg]

Yes, Panama, please clarify. It sounded like you were inadvertently describing the grout in post #3, rather than the setting material. I want to make sure the setting material was also a powder mix and not something pre-mixed from a bucket.

[Flyingscot]

It looks exactly like what happened when I stupidly used mastic for a tiled shower floor years ago. The discolored grout was mold.

[Tool Guy - Kg]

Yeah, you need solid support under the tiles. If mastic was used, it might not be dry and rock hard. And this would lead to discoloration and slightly rocky tiles from foot pressure that could leave cracks around some tiles.

[Panama]

I apologize...my computer was down and I finally got it working!

The color of the grout is LIGHT PEWTER, LATICRETE 1600 UNSANDED GROUT. It was a powder mix. The joints are 1/8". I can take additional pictures if it would help. Thank you all so much!

[Panama]

This is the marble I used in the shower-- Calacatta Gold Herringbone Italian Marble • Finish: Polished • Each sheet cover one square foot • 8 Columns by 8 Rows • 64 Stones per Sheet • Sold by the square foot • Thickness 3/8" (10mm) • First Quality