Why is the grout in my tile floor cracking?

Answered by Jeffrey ~ February 28, 2012 ~ No Comments

Several months after remodeling our bathroom, the grout in the tile floor is cracking and small chunks are breaking loose. We installed the tile and grout ourselves, as well as a layer of cement board underneath the ceramic tile. What is causing the grout to crack and how can we prevent it from happening again when we tile the kitchen floor? Thanks.

Mark Orlikowski ~ Traverse City, MI

Jeffrey Anderson

Hi Mark. There are a number of reasons why your bathroom tile flooring may have the grout cracking, but I think it's highly unlikely that it's due to where you purchased the grout. The most common reason for grout to crack is due to the tile moving and placing stress on the grouting. This could be caused by:

  1. The sub-floor moving -- it doesn't sound like you attached the tile directly to your sub-floor, but while the plywood or OSB may seem solid, even a single loose board can cause a problem. The fact that the grout is cracking in both the shower and primary floor would lead me to believe the sub-floor is not the problem unless the joists underneath can't handle the weight.
  2. The underlayment moving -- if you used an underlayment and it wasn't secured properly to the sub-floor, it could be moving slightly as your family walks across the floor. All it takes is a little movement to cause grout to crack.
  3. The thinset base isn't sufficient -- if the tile flooring was installed over a thinset base and it wasn't thick enough, the edges of the tiles may be moving and causing the grout to crack.
A few of other issues that can cause grout to crack are that the incorrect type of grout was used for the amount of spacing between tiles, the grout was mixed incorrectly, or that you didn't allow for expansion around the edge of the room or shower pan. If non-sanded grout was used and your joints are larger than 1/8 inch, it may start coming out in the chunks you describe. The same can happen if the grout wasn't mixed thoroughly or in correct proportions.

Lastly, all wood expands and contracts with temperature changes -- even inside your home. If you didn't leave room for expansion at the room edges, when your walls expand they can put stress on the tiles and cause the grout to crack. I'm sure it gets fairly cold in Traverse City, MI so between heating your home during the winter and letting it cool down during the summer, there is probably a lot of movement going on.

As you can see, there are a lot of reasons why your bathroom grout could be cracking. You may want to have a flooring or tile professional take a look at it to see if the correct reason can be determined prior to moving onto your kitchen floor.

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