Why is my Floor Grout Cracking?

by Roger

Your grout is cracking for one reason and one reason only: your tile is moving. That’s it. Okay, that’s not it – Unless your grout is non-sanded and was installed in the last 28 days – your tile is moving. That’s it. Yes, 28 days has significance, it is the amount of time it took my teenage son to clean his room. It is also the amount of time it takes for grout to fully cure.

So let’s figure out why your grout is cracking:

Your grout is newly installed – incorrectly

If you do have grout that was installed within the last 28 days then your grout is not actually cracking – it is shrinking. Either your grout lines are too large for non-sanded grout (smaller than 1/8″)  or it was incorrectly mixed. NO! You cannot simply mix up more and fill it in. Read this post about adding more grout to your grout lines.

If your grout is not fresh, well, you need to repair the reason your tile is moving. And stop using your pogo stick in the house. Diagnosing the reason your tile is moving is extremely varied. It could be anything from inadequate deflection in your flooring for the type of tile all the way up to and including the aforementioned pogo stick.

The most likely reasons your tile is moving:

Your tile does not have proper thinset coverage

The most common reason I run into is improper coverage. This simply means that there is not enough thinset beneath your tile to properly adhere it to your substrate and support it. If there are any unsupported areas beneath your tile along the edge or in the corner of the tile, walking on it will eventually work what little support it may have loose and the tile will move down and up every time you step on it. The tile moves, the grout does not. The grout loses the battle and starts to crack out. By ‘crack out’ I don’t mean like that ridiculous Intervention show on cable, I mean it will start to crack and come loose.

To fix this you need to remove and properly reinstall the tile. If it is only one tile it may be an isolated incident in your installation and you will be fine. If you have cracked grout all over your tile installation it was either improperly installed or . . .

Your subfloor is moving

If you have a wooden subfloor and your tile is directly installed to it – go pick out new tile. That is more than likely an improper installation. While tile can be installed directly to plywood it requires a VERY specific method. And I do mean very specific. More than likely it is simply installed improperly probably by someone that did not know any better. If it was properly installed over plywood, well, your grout wouldn’t be cracking. Start reading this paragraph all over. Or . . .

Your backerboard was improperly installed

If you have Hardiebacker, Durock, or any other type of cementious backerboard beneath your tile it should have been installed in the proper manner. It needs to have thinset beneath it, it needs to be screwed down (properly), it needs proper spacing, etc., etc. Read How to Install Backerboards for Floor Tile to see all the things that should have been done.

More than likely there is no thinset beneath your backerboard. Thinset is not used to adhere the backerboards in any way – it is used simply to fill voids beneath the backerboard. It is placed there specifically to prevent your tile from moving. Moving tile leads to cracking grout. But you knew that – or you should start reading this page all over. This would be another time to start shopping for new tile.

Other reasons your tile is moving

You do not have expansion space around the perimeter of your tiled room. No, the tile will not expand – but your walls do. If there is no space between your tile and walls it will force all the pressure into your tile. This will cause cracking grout and, eventually, ‘tenting’ of your tile.

You do not have expansion joints in your tile. For every application there are specific spans of tile which can be installed before a ‘soft joint’ is required. This is simply a grout joint filled with a matching caulk or silicone to allow for movement without cracking your grout or tenting your tile. Most of these measurements are over 25 feet. So in English: if your room is not 25 feet long or wide this is not the reason your grout is cracking.

If your tile is on concrete – directly on concrete – your slab may not have proper expansion joints or the tile installation did not honor those. If installing tile directly to concrete (and you should not) there needs to be a soft joint directly above, or two inches on either side, of the slabs expansion joints. If not your slab will move differently than your tile.

And there could be a host of other, less apparent or less common problems. However, if your grout is cracking it is probably for one of the reasons above. The method of repairing it depends entirely on why it is cracking. Most of it, as with most tile installation problems, is due to improper installation.

Or your pogo stick.

If you have any questions about the proper way to repair your tile or grout just leave a comment. I answer every one of them – really, look around the site. I’m just super cool like that.

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Betsy

Hi Roger – this is an interesting post. I have long assumed the problems with my tile cracking were due to the installation. The contractor installed a new subfloor, then electric underfloor heating. He put a layer of mortar on top of the floor heating mat, then installed floor tile on top of that. He also installed tile half way up the walls of the bathroom. Within a few months of the installation, I noticed small hairline cracks in the floor and wall grout. There are no loose tiles. I notice the cracks and although I don’t know if anyone else would I think a home inspector would probably see them and question the quality of the installation. Is there anything I can do to improve the appearance of these small cracks, such as applying a thin coat of grout over top of the cracks? The cracks are mainly in perimeter of the room (where the floor joins a wall, tub, or other vertical structure) and where ever there are corners.

Reply

Roger

Hi Betsy,

If those are where your cracks are then your installation might very well be just fine. Any change of plane requires caulk or silicone, not grout. Different planes will expand and contract in different directions. Silicone can compensate for that, grout can not.

Reply

Shirley

I have some grout that is cracking and you are right, the reason it’s cracking is because the tile is moving. In fact, the tile comes right off. I also see that the tile was installed over K3 or particle board which was installed over the plywood. The tiles were fine for 2 years before the cracking appeared. Can I just try and reinstall the 2 tiles by making sure there is plenty of mortar under the tiles?
Thanks,
Shirley

Reply

Roger

Hi Shirley,

You can, but you’ll be replacing them, along with more cracked tiles, sometime in the near future. Your floor is built improperly, there is no fix short of replacement.

Reply

Joyce

i had a ceramic tile floor installed over a wood floor. there are spots where the tiles are cracked and the grout has come out in chunks between many tiles. You can feel the floor give in some spots. Can this be fixed or should i just replace the floor with something else which is what the contractor recommends.
Thanks
Joyce

Reply

Roger

Hi Joyce,

Something needs to be replaced. How much of something and specifically what depends on the reason your floor is cracking. In nearly every scenario it is improper substrate preparation, which calls for removing existing tile and floor and rebuilding properly.

Reply

Curt P

Further to my grout cracking, what about a flexible grout such as Quartzlock2?

Thanks again

Reply

Roger

Hi Curt,

Again, I’m not sure which grout cracking you’re speaking of. Quartzlock 2 does not have significant flexibility properties either.

Reply

Curt P

Hi Roger,

Yes, it is bonded to the plywood and was backbuttered everywhere.

What about a urethane grout as I’ve read they have a decent amount of flex?

Thanks

Reply

Roger

Hi Curt,

Urethane grout does not have any significant amount of flex. Beyond that I have no idea to what you’re referring as you have not typed this as a response to my (assumed) question or answer as instructed above the little box you typed this in. I have (literally) over 20,000 questions here, I can not memorize every person’s project. :D If you can ask again as a reply in the proper place I can probably help further.

Reply

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