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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Hi ROger,
We just renovated our entire kitchen. It was finished it December. In February I noticed that a tile seemed loose. Then the grout started to lift. Now I feel like the loose tiles are spreading. There is an electric heat mat under the tile. I called the contractor and he came to look at it and thought it was the thin set issue. Not sure what to do. Should we just replace the few tiles ( but what if loose tiles spread) should we get all new tiles or can we install wood floors??? Quite upsetting as we waited years to renovated the kitchen. Thank you for your advice!!



Hi Judy,

It could be several reasons, but I would need detailed specs about the construction of the floor to nail down the cause definitively. A couple things to check:
1. Pull one of the tiles up and see if there is any thinset on the back of the tile.
2. If there is an slc (self-leveling cement) product over your heating wires check to see whether it is stable and intact.

Start with those two things and, if you can, let me know the specific construction of the installation as far as the substrate, method of heating and specific products used.


Dan Nelson


Hi Dan,
I thought I knew my stuff because I did many of my bathroom floors in the past and they still look great. This laundry room projects got me confused. 12′ by 6 1/2 room, new sub floor screwed down, 12×24 thin (standard) ceramic tiles with 1/8 gap spaces, lots of thin set applied. I grouted next day with a none sanded hand mixed grout. Three days later we started walking on it and a few days after that I noticed grout cracking away from the tiles in the high traffic areas. It only got worse from there. So, during the process of fighting all the old grout out, I noticed that there are a few tiles that have incremental movement with full weight applied. Also, I must add that I used only a large bottle of grout strengthener to mix the grout (no water) and it started to dry up just before I could finish.

I’m ready to fill the gaps again but don’t want to make another mistake. How should I proceed? :whistle:




Hi Dan,

What, specifically, is a ‘new subfloor’? Wood? Was the tile bonded directly to wood or is there a proper substrate beneath it? And what, specifically, thinset was used – brand and type? Customblend? :D And what is ‘grout strengthener’? Something like grout boost? (I hate that shit…).

I need more info to help. Help me help you. :D



1 or 2 tiles are moving was installed over 10 years ago whole kitchen hall and bathroom cement floor had it installed so not sure so is removing all of the tiles my only option?



Hi Sandra,

It depends on what kind of shape your installation is in. If it were mine and I didn’t want to replace everything I would likely just pull up those loose tiles and reinstall them. It may be just fine.



Hi Roger,
We have placed marble tile in our bathroom and allowed 5 days for the thinset to set. Today we went in to clean off some dried on thinset before grouting…only to find one tile didnt set properly and was loose. We were able to literally just pull it up without much force. So then we cleaned the dried thinset off and back buttered new thinset on and replaced that tile. The thinset says wait 48-72 hours before grouting…does this mean we actually have to wait another 2-3 days to finally grout the whole bathroom? Then wait another at least 3 days for the grout to dry before re installing the sink and toilet?? This project has taken us a total of 2 weeks so far…first time laying tile. Any advice would be appreciated! Thank you!



Hi Kie,

No, go ahead and grout it all tomorrow. It’ll be fine. You can set the toilet too – get this damn project finished already! :D


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