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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Hello Roger,

I tiled my lounge (never done tiling before) with 44cm tiles and 1cm spacers, but the grout in some areas has ‘sunk’ leaving deep grooves between the tiles. Is the reason for this that the space between the tiles is too big, and where did the grout go? It looked ok when I first did the job. Needless to say, the wife is not happy and muttering about getting proper people to do these jobs as she is finding the valleys between the tiles difficult to clean. And can I just add more grout where required or do I have to replace it ?
Thanking you in advance,




Hi Roger,

I’ve got a 5′ x 16′ concrete slab at ground level inside my house I want to cover with 14″ square porcelain tile, as well as concrete steps going down to the basement. Like everything else tile related, there seems to be 100 approaches suggested, and I just want someone smarter than me to tell me an easy solution for an amateur. I know I’m not supposed to put tile directly onto the concrete slab, but is that even true for really small areas like the steps, or the 3’x3′ landings I have at the top and bottom of them? Would it be sufficient to use redgard and then (modified?) thinset on top of that, or do I need something like ditra? I’ve never used ditra before so I’m trying to avoid it if I can, but I don’t think the added height is an issue.

Also with the steps, I see schluter makes stair nosing profiles (the TREP series) but they’re almost $40 a tread. Is there a cheaper option? The tile I have is non-slip, can I get away with using an outside corner trim piece like schluter rondec?

Thanks for your help.


Stewart Beller

Porcelain tile installed in my bathroom everte we shower ther is white spots on the tile contracter thougt it was haze had it cleaned pressure washed made it worse. I no it’s the grout coming off tile is done nice and tight I think they used unsanded grout how do I fix that can we just take out the grout and use new grout



Hi Stewart,

Yes, you can remove and regrout your tile.



I have granite tiles on my living/dining room floor, in the Philippines, set on concrete base. They have lifted for the second time now. They are set very tight together, with no grout, which seems to be a local procedure. We thought they lifted because the concrete rose up, but this time it does not seem that is why.

Any idea why they are lifting?



Hi Eva,

No grout or compensation for movement will cause pressure to build up in an installation and that pressure must go somewhere. It often sheers the tile from the underlying substrate. You need compensation for movement, especially in extremely humid areas such as the Philippines.



THIS EXPLAINS EVERYTHING. YES I’M TYPING IN ALL CAPS BECAUSE IN MY HEAD I’M YELLING. I JUST WANT TO CRY!!! My husband installed wood look tile in a bathroom. After a few months the grout in a small section has started cracking. Ever since it was installed I could feel and hear a little “creaking” over a few of the tiles. We are supposed to be listing our house on Friday. Now we have to fix this! Ok…pity party over. We can do this. :)



Hi Roger.

I’m from the Philippines…Quote:” 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.”…Cracking grout, tenting tiles happened this morning after 18 years, is it possible? Thanks!



Hi Maricel,

Absolutely it is. 18 years of expansion and contraction finally put enough pressure on the installation that it needed to release somewhere. If you can remove those tiles and reinstall them with a soft joint they should be fine for as long as you want to keep them.



Do you have a link to the very specific way to lay tile on plywood subfloor!



Hi Amber,

I can not find a specific link, but it really isn’t difficult. Just make sure that your top plywood seams are offset from the bottom ones (which should be directly over a joist) by 1/3 the length and width of the plywood sheet, ensure your joints are staggered (so you don’t have four corners in any area) and only screw the top layer into the bottom layer, not into the joists.



Thanks Roger- Yes, I back buttered the tiles. I’m not sure the exact distance of support for the joists, probably somewhere around 12 feet is my guess from remembering what it looks like in the crawl space. The part that is most perplexing to me is how things have changed now that the air is less humid. I guess tile removal is in my future…thanks again.



Hi Roger- I’m hoping you can help me out with a rather frustrating and puzzling tile issue related to cracking grout. I installed 600 sq feet of 18 inch porcelain tile last February in my kitchen/ front hallway. About 3-4 months later I noticed the grout began to crack in high traffic areas. Over the next few months I noticed small cracks even in non traffic areas (closet) and in high traffic areas grout crumbling. You could feel the tiles move when stepping on those where the grout completely failed. Here is the info for installation. 2 layers of 5/8 tongue & groove plywood over 2×6 16 inch on center. Modified thinset with 1/4 notched trowel, ditra membrane, unmodified thinset with 1/2 notched trowel, tile, sanded grout with 1/4 inch spacing. This is my 3rd time using the ditra & I’ve never had this problem before. I’m torn about whether it not to pull up what I have access to (installed under my new caninets) and start over or just regroup & see if it cracks again. Of interesting note, now that it’s winter and the humidity is down ( we lice in virginia) the cracking has stopped and the tiles no longer move or creek when you step on them. Any ideas?



Hi Emilie,

Do you know the unsupported span between your joists? While they may be 16 o.c. they may have a large span, lessening the deflection ratio. That may be the issue, but it sounds more likely to me that the tile itself is not bonded correctly to the ditra. Were the tiles backbuttered? The first step to determining the problem would be to pull up one or two tiles and see what type of coverage you have on the tile.



Hi Roger. I’m a snowbird and spend winter (Nov-Apr) in Phoenix, Arizona. I had my bathroom tiled about this time last year. Upon returning to Arizona I noticed one area where the grout has chipped out. The bathroom is only about 7 ft x 10 ft so I guess one tile isn’t bad overall. The problem is that the contractor came back the mid January and regrouted that area and now it has separated from the tile and is beginning to crack again. When the tile was installed, backerboard was put down, but I don’t remember if any thinset was put down first. As I said it’s just the one area. No other tiles have grout that is cracking or chipping out. What do you think the problem might be and what can be done to correct this? Thanks.



Hi Cleo,

I’m thinking that the area cracking is directly over a seam in either the backer or subfloor and the backerboard seams were not taped and mudded. It could also be that there is no thinset beneath it. Either or both could cause that. The tile will need to be removed, the source of the problem identified (likely one of those) and fixed. Regrouting it will just lead to the same issue.


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