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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Bill

I recently installed floor tile for the first time in my 40 square foot bathroom. Tiled area is roughly 6ft x 5 ft. I started by putting 1/2″ sanded exterior grade plywood over my diagonal plank subfloor. I then put polymer-modified thinset down, a Nuheat mat, and another layer of the same thinset, then Ditra. I allowed the thinset under the Ditra to dry for about 4 days, then used unmodified thinset over the top to install my tile. I might have gone a little thick in spots, as there were some uneven spots (less than 1/8″, in my estimate) after I laid down the Ditra, and I filled them in with the final layer of thinset). My floor has been curing for about 40 hours now, and when I step on the ends of my 4″ x 19″ ceramic tiles (1/8″ grout spacing), I feel them moving up and down slightly. They are not moving laterally, and I’m sure I used enough thinset, but I’m concerned I might have used too much in spots. Weather here has been warm and humid (80 degrees and dewpoints in 60′s), but typical of Wisconsin summers. Any ideas why this might be happening? And should I just wait a week before grouting, stay off tile, etc. etc.?

Reply

Roger

Hi Bill,

Did you wait a day between each layer? If not then your thinset is likely just taking a lot longer to cure. Wait a week or so and see if it does the same thing, it shouldn’t.

Reply

Bill

Thanks Roger. I didn’t allow separate curing for the two layers that sandwich my Nuheat mat – did both layers at once and laid the Ditra on top. Total amount thinset was less than 1/4″, though. The modified thinset under the Ditra had about 4 days to cure before I laid any tile – and it felt very solid when I started laying tile.

I will wait a week or so before grouting. No hurry as I’m waiting on the electrical inspector before I can proceed with anything else. I suspected the top layer of thinset might need a little extra cure time, with the large tiles and small grout spacing. I’ll try to stay off it until the inspector arrives, and resist the urge to keep checking it daily.

Reply

Brenda C.

My dad worked to install ceramic tile planks in a 6 ft x 8 ft corner of our family room on composite tiles (from the 60s) which were installed on cement slab. (The whole house is cement slab. The grout started popping the day after he grouted. He knew I was from movement and has he lifted up a few random tiles, he could see the thin-set was still wet (even after a couple of days). And as he removed the original thin-set, the Eco-prime multisurface adhesive also came up with it. He reset the random tiles since he could also see large areas of the tile where no contact had been made with the thin-set. After resetting the random tiles with more thin-set, he recommended we wait a week before regrouting..,and then recommended the flexible grout.

From the information I have shared, do you have any additional questions? What advice can you give me?

Reply

Roger

Hi Brenda,

Did you ask the tech department at eco-prime whether their product was approved for use over your particular composite tiles? The problem, I think, is adhesion of the eco-prime to the composite, if that doesn’t bond correctly it doesn’t matter what you use over it, that layer is not bonded which means nothing above it is. I would contact their tech line and see what they have to say.

Reply

Lulu

Hello, I’m in the process of buying a house when I noticed a continuous hairline crack in the grout from the laundry room through the hallway, kitchen and ends in the breakfast area. Is this a sign of bad grouting or something more serious like an issue with the foundation? Thank you.

Reply

Roger

Hi Lulu,

I have no idea. You haven’t mentioned whether it is over concrete or plywood, how old is the installation, what type of grout (sanded or non-sanded), etc. If it is tile over wood with sanded grout it is likely inadequate substrate preparation. If it is over concrete it is likely lack of perimeter and/or soft joints. If it is a new installation, especially with non-sanded grout, it is likely grout shrinkage.

Reply

Phil

Installed tile in kitchen on 1″ Mud floor base with thinset. Use non sanded grout small grout line 1/16? the grout is disapearing in some sections between the tiles and when you tap tile it sounds hollow. This started 6 months after installation. Today i refilled the missing spots and forced the grout to fill voids(hopefully). Do you know what causing this?

Reply

Roger

Hi Phil,

After six months over a mud bed it is likely that you just didn’t get the grout lines filled enough, causing grout ‘bridges’ where it looked like they were full, but had a hollow spot beneath. It’s easy to do with non-sanded grout. If they do it again, especially in the same places, then there is either movement or the tiles are not bonded correctly.

Reply

Steve

Mr. Elf,

This is my situation: I live in a condo in a house from the early 1900′s which has 2×8 floor joists that are 16 inches apart and span the distance of 13 feet. The subfloor itself is on two layers of 3/8 plywood (nailed together). There is underfloor heat beneath the subfloor (hot water). The floor was very out of level so my tiler primed the floor and put self level on it. He tiled on top of that, of course using thinset, and put sanded grout in between the tiles. He put matching caulk where the walls meet the floor. Now some of the grout has started cracking. My vanity is placed on top of the tile on his recommendation, it is not tiled in.

The same tiler also tiled my neighbors condo beneath me in a similar manner. He has the same problem, but it’s very mild compared to mine. However, since he lives on the first floor he had the benefit of having sistering joists (added later), instead of single ones that I’m stuck with.

So my question is: is the cracking of my tile caused to incorrectly tiling over the self-level, due to the poor joists (too much bounce), due to the heated subfloor or some other reason, and what can I do to correct this? I’ve read through this article many times, but I can’t trouble shoot the situation by myself.

Thanks.

Reply

Steve

Correcting a minor detail: the grout now has hairline cracks across 1/4 of the room, which is 8×9 ft in size. The tiles are not cracked. The installation was done a year ago. Some of the cracks appeared immediately (within a week), others took 2-3 months to appear. It seems that the situation is not getting worse, but I’m concerned that eventually my tiles will start cracking as well. I was hoping to keep this bathroom for decades to come.

Reply

Roger

Hi Steve,

It sounds as if your floor joist system is not supporting the tile. He should also have installed at least another layer of 1/2″ ply. It should be a minimum of 1 1/8″ ply even under slc. It’s hard to be certain from here, but I think it’s simply inadequate substrate preparation. The two 3/8″ layers of ply is actually weaker, although it’s 3/4″ thick, than one 1/2 layer of ply.

Reply

Alison

Hi Roger,
I had a new kitchen installed last February/March and the grout is cracking in several places across the kitchen floor. Is this most likely due to the thinset? I wanted to find out before contacting the people who installed it to make sure they were definitely liable!
Thanks.

Reply

Roger

Hi Alison,

It’s due to movement somewhere. I would need to know how your floor is constructed to even venture a guess as to what is causing it. I can say, however, that it is their fault.

Reply

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