Why able I getting Hairline Cracks in my Carrara Marble Shower?

QUESTION

I have a marble shower in which the wall marble tile is 12"x24" x3/8" cararra marble.

We are getting many "smaller than" hairline cracks in the marble in a half a dozen places. You can barely even feel them.
It's a large shower. The walls are 6' wide and 9' tall.

Any thoughts?

ANSWER

ANSWER - Generally speaking cracks are either reflective cracking where the underlying substrate has a crack or separation and it telegraphs through the marble or there is structural cracking where the structure has excessive deflection or other structural issues.  Or it is a compressive crack where the stone is not fully supported with the thin-set adhesive that leaves voids and there is a load applied to the stone causing the crack where it isn't supported.

Since you said it is smaller than a hairline crack and you can barely feel it, it leads me to think that you might have what we call indent fractures.  Typically this is caused by excessive shrinkage in the adhesive, if it is applied too thick, or within the substrate if it develops shrinkage cracks for one reason or another.

Initially indent fractures don't actual crack the surface. It is a very slight depression.  If you put a straight edge over it and shine a flashlight behind the straight edge you will see a small gap at the indent.  Typically you can only see these indent fractures from an angle when light shines on it, otherwise it isn't notice able.

Indent fractures can develop into actual cracks if it is subjected to enough stress since it is a weak point, but often they don't crack.  If it is an actual crack then you have to remove the tile and look for the evidence to explain what caused the crack, and the determine how best to remediate the problem.

2 thoughts on “Why able I getting Hairline Cracks in my Carrara Marble Shower?

  1. Lauren says:

    We just finished a long reno of a second floor bathroom (it was gutted). The floor tile is called a zebra marble (it has vey straight gray and white stripes running through it) and looks beautiful. However, during the course of the reno we started to notice that people who were working in the bathroom were leaving unsightly chips in the tile, which was alarming. That was the least of or problems, apparently. About a week ago I noticed what looked like a crack running from the exterior wall through the tile (the crack is underneath or inside the tile as there is nothing on the surface). Over the course of a few days (and to my horror) the crack extended through five more tiles running almost the entire length of the floor. It’s crazy—the crack runs a path and crosses grout lines, but no grout is cracked (at least on the surface). Another crack has also extended outward perpendicularly to the first, starting at the vanity. The contractor of course said he has never seen this happen in all his years in the business, and is coming to look at it with the tile setter in a couple of days. I am in shock as we just finished the project and the thought of everything being ripped out makes me want to cry. There is an electric radiant heat pad installed underneath—not sure if that has anything to do with it but it will obviously be destroyed when the tile gets taken back up. I have been reading some of your posts on indent fractures but although you can’t feel these on the surface you can easily see the big long crack as soon as you walk in, so nor sure it’s that. Project was started in June and recently completed (it took forever!) and I also wonder if the change of outdoor temp from hot to cold comes into play, although this has never happened before. We have a radiant floor system in a bathroom in the basement (porcelain tile) and the temps fluctuate much more down there, and we do not have a problem with it. I’d love your thoughts!! Thank you!

    • Donato Pompo says:

      If you see what appears to be a crack in your stone floor, but when you touch it, you can’t feel it, then it is an indent fracture. Normally the crack in the floor is only noticeable under certain lighting conditions. If you put a straight edge over the crack and put a flashing light behind it, then there should be a slight gap further indicating it is an indent fracture.

      Normally indent fractures occur from excessive shrinkage in the thin-set mortar adhesive or the mortar bed below it. Often the excessive shrinkage is due to too thick of thinset or mortar. Once the cracking occurs in the underlying materials then the crack will telegraph up partially into the tile which creates the indent condition.

      Eventually if the tile is subjected to a certain degree of stress, the intent fracture might turn into an actual crack.

      The only way to know for sure what is causing the condition and to know how to remediate it, is to have a tile expert carefully remove the affected tiles to look for the evidence.

      Normally stone will only chip if something heavy and sharp is dropped on it. So that isn’t normal.

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