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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Danny candler

I just had tile installed on the bathroom floor and walls and shower. The tile is Installed over 3/4″ plywood with 1/2″ durock. They did not put thinset under the durock but they did screw it down. One thing they did that concerned me was put a dehumidifier in the room each night to try and speed up the drying process since they were in a hurry to finish. Now there are hairline cracks in the grout on the floor, walls and in the shower on sporadic areas. Also the crack will follow the edge of a tile then jump across to the other side of the grout joint so it’s not just along one edge. Do you think using the dehumidifier may have prematurely removed moisture in the grout and/ or thinset??, any ideas. I am getting ready to make a bad phone call to the contractor. Please advise. Thanks.

Reply

Roger

Hi Danny,

Yes, I absolutely think that. Grout cures through hydration, which means that the longer the moisture stays in it the stronger it will cure. Premature drying will cause it to shrink excessively and become weak.

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Robin

Hi Roger,

I have a new build house with a block and beam floor, on top of that is 4”kingspan and underfloor heating. On top of that a is 3-4” wet mixed concrete slab. Tiles were laid on top of this with a tile adhesive mixed with latex. There is a gap around the edge of the tiling(under the skirting boards). When stepping on the tiles they mostly sounded hollow and after a week or so the gout started to crack up especially in the heavily used areas. On lifting one of the tiles it was fixed in the centre of the tile but was loose on all the corners. The builder then repaired the fix with some sort of expanding wood/ceramic and concrete glue and re-grouted. This is happening all over the kitchen/hall and utility room now. We have not had the under floor heating on since the house was built, I am guessing this will make the problem even worse. What should I do? Is the builder just doing a quick fix?

Reply

Roger

Hi Robin,

Yes, it sounds like he is. If tile is being laid over that type of construction it should be deck mud – not concrete. I have no idea what he has going on there but it’s nothing I’ve ever heard of.

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Sara

Hello there! My better half and I bought a home a few months ago with a (I think) ceramic tile kitchen floor. I haven’t ever been a fan of tile and grout, and I think I cracked a joke to the home inspector about all of the grout falling out after I noticed some pinholes and separation along the edges of the tiles. The inspector assured me nothing was wrong. Today I was sweeping the floor and noticed a long slice of grout had come up and was being swept into my dirt pile. A few places are crumbling, especially near the deck access sliding door, and the cracks and divets I noticed before seem larger and more pronounced. The side edges of the tile are exposed in a couple places near the door.
The only clues I have to go off of as far as installation is a flyer I found on the fridge when we bought the house for a ceramic tile and stone installation guy as well as a quarter of a bag of sanded grout. The grout lines are a quarter of an inch wide.
Your help and insight is appreciated!

Reply

Roger

Hi Sarah,

It could be a number of things, but my guess would be inadequate floor preparation in some manner. Either there is not a proper tile substrate like backerboard beneath your tile, or, if there is, it was not properly installed (no thinset beneath the backerboard, for instance).

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Rich

Thanks Roger! :-D

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Alison

Hi Rodger,

I had a new kitchen installed 18 months ago and now the grout is cracking in several places across the floor, we had to lift a couple of tiles (under the tumble dryer) as we needed access to underneath the house and found the tile just lifted off the adhesive with no force required whatsoever. The adhesive underneath was completely cracked and about 20mm thick. There was also another tile under there. I contacted the joiner who oversaw the original work and he came to have a look and said they needed to level out the floor because from one side of the kitchen to the other was uneven and this was the way to do it. I am wondering what is causing the cracking elsewhere and should he have made the adhesive so thick? And do you ever use tiles piled on top of each other to make a floor level??! The tiles are laid on top of plywood (and clearly different thicknesses of adhesive!) He also claimed the cracking grout was due to air bubbles and was ‘just one of those things’. Your advice would be appreciated! I don’t really want him to come back and just fill in the gaps as he suggested!

Alison.

Reply

Roger

Hi Alison,

No, tiles are not used to make a floor level. Thinset should not be used that thick, ever. If the floor needed to be leveled it should have been done done with slc or an approved product, not thinset. It is cracking because thinset installed that thickly will shrink, and continue to shrink. That doesn’t even take into account that the tile is apparently not bonded correctly to begin with. ‘air bubbles’ (bullshit) and cracking grout are NOT ‘just one of those things’! Your installation is clearly not installed anywhere close to proper. It needs to be removed and built correctly. I wouldn’t let him anywhere near it.

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mark

HI Roger, I have a pillar and post system under my house, The house was built in 1910. The house was re-pillared and posted when i bought it(re-leveled. I had a contractor remodel my bathroom. My bathroom tile was put on top of 1 3/4 inch plywood substrate. Everything was good for 2 years. Now the area between the bottom of my tiled walls and the tile planks ( entire perimeter) has been cracking. It looks like it like a hairline crack, but it is big enough for a cockroach to come through. What can i do? re-grout along the entire perimeter? or should I use a color caulk. Ive noticed that you can really only get white caulk. I have used a sanded caulk in my other bathroom but it is already cracking. The area I live in has major clay. Is this going to be a problem with the swelling of the clay when it drys out and contracts? The sidewalks are all tilted and moving in the area I live. I dont have a lot of water around the house, but this has been a continuous problem. Mark

Reply

Roger

Hi Mark,

Structures over clay are going to move more, nothing you can do about that. You can get colored caulk in nearly every grout color from the grout manufacturers, but if I were you I would use 100% silicone, which can also be had in every grout color. Check out laticrete colored silicone or color-rite, both are very good products. Any change of plane (wall tile to floor tile) should never be grouted, they should always be siliconed.

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rspicer

Hi, Roger,
My brother has had lots of experience tiling and grouting. He came over to help us retile bathrooms and the laundry room. The day after I wiped off the grout, I began noticing crumbling along one tile. the more we walked on it the more it spread. I have very painstakingly removed the grout so it will not spread anymore. My question is should I regrout or should I remove the offending tile first? How do I remove the tile so that I can reuse it? (it is in the middle of the room.)

PS This didn’t happen on any of my brother’s other projects.

Reply

Roger

Hi rspicer,

Yes, you should remove the tile to see what is causing it to move. It’s doubtful you’ll be able to reuse it. You can try to pry it out with a screwdriver using a piece of cardboard beneath it as you pry against the adjacent tile, but I really wouldn’t count on it coming up in ones piece.

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Rich

Hi Roger,
I had my hallway and kitchen covered with porcelain tile flooring over a year and half ago during our kitchen renovation. After less than eight months following completion of the installation, I noticed cracks in two different grout lines extending across my hallway, wall to wall.

I surmised that had to do with the fact that the contractor who laid the tile did not tape the ¼” backer board that was used throughout the installation since the cracks in the grout line occurred at exactly five feet apart (the length of the backer board). Giving the contractor the benefit of the doubt, I had him remove the cracked grout and re-grout between the tiles in these sections. However in less than 10 months, I noticed ‘hairline’ cracks appeared in the re-grouted joints.

My subfloor sheeting consists of 5/8” tongue and groove plywood, the joist are 16” on center, and the original flooring was 12” x 12” (approximately 3/32” thick) vinyl tile which was not removed because we thought it might contain asbestos (in either the vinyl tile or adhesive or both since my house was built in 1972). I also observed that the subfloor sheeting seams occurred almost directly beneath the ends of the backer board that was not taped.

I realize now the contractor should have used ½” backer board and taped all the joints but in over a year and a half since the project was completed, I have not noticed any other cracks along any of the other grout lines.

Another flooring contractor was called in by the company that did my floor (at my request) and told me initially that the entire porcelain tile flooring should be removed. If this were to occur, I’d have to remove all my new floor cabinets and countertops, not to mention redoing the backsplash along back side of the sink since everything would be raised by ¼”.

Thus my question: Do I need to pull out the floor cabinets and countertops and redo all the flooring which extends wall to wall or can I just have the contractor cut out the porcelain tile on both sides of the cracked grout joints, clean off the old tin set from the backer board, then tape the backer board joints, reapply thin set then replace the porcelain tile back over the sections were it was removed?

The latter would sure make life a lot easier since the only other viable option offered by the contractor was to remove all the porcelain tile and backer board that was not under the cabinets. I don’t care much for this option as it would defeat the purpose to protect the subfloor by creating a new ¼” lip and seam along the base my cabinets, making it difficult to properly dry the floor if a ever spill occurred and it got under the cabinets or if my dishwasher leaked.

I’d appreciate your thoughts.

Reply

Roger

Hi Rich,

1/4″ backer can absolutely be used as a substrate on a floor. However, a couple of issues are incorrect. It seams you only have one 5/8″ layer of T&G ply over your joists??? You should have a MINIMUM of 1 1/8″ double layer of ply beneath any tile substrate. There should have been another 1/2″ layer of ply placed over that. The backer also needs thinset beneath it – you did not mention whether that was done or not. And of course mudding and taping the seams, but you knew that. :D

Your fix over the cracked lines MAY work, but I certainly can’t guarantee anything as there are other issues present which may cause problems in the future. It would certainly be much easier, and it may fix the problem, but it may also only fix the problem there and other areas may begin to crack. You can have him do that to see if it works, but I certainly don’t think he would be willing to guarantee anything with that sort of fix. All that said, it’s definitely worth a shot.

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Kim Milton

Hi Roger,

My husband tiled our bathroom floor and I grouted it. The floor is made of chipboard and then we have put cement sheeting over the top and tiled. Unfortunately our new toilet leaked under the tiles and grouting. We removed all the grout and regrouted. Most of the grout is fine but there are two spots that keep cracking and crumbling. One is right in front of the toilet and the other spot is when you walk in. Can you tell me what I am doing wrong and how I can fix it please!! Thank you Kim

Reply

Roger

Hi Kim,

I think some of your wooden substrate beneath your backerboard has gotten wet and swelled, which weakens it and creates voids in it. If that’s the case it will need to be replaced or have another layer of ply put over it beneath the tile.

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Grace

Hi,
I need to educate myself on grout. I had a major company, who subs out jobs, install my wood look tile over a concrete slab that had carpet. They leveled the floor at an unquoted price gouging rate, that took a day with four hours total labor. Then they returned the next day super early and worke all day and laid and grouted the tile. In the same day. It has been over a month and my gout is crumbling. I noticed air bubbles first then in traffic areas I noticed it coming up. Not cracking, crumbling. The guy came out and you could take a car key and it just scratches up in a dust. My goal is to educate myself since now I trust these guys about as far as I can throw them. What could have happened to the grout in this process to cause it to crumble? He plans to contact the manufacturer of the grout and says most likely they will have to scrape it all out and re-grout. Please Please advise. Thank you.

Reply

Roger

Hi Grace,

It will have to be removed and regrouted. It is likely due to improper mixing of the grout (WAY too much water added) when it was installed. If too much water is used to mix it the grout will not be compacted enough, once the water dissipates you have grout that is very weak, which leads to what you have now. I’m sure the manufacturer will tell him the same, although he likely won’t tell you that. If I were you I would call the manufacturer myself and see what they tell you, that way you know what they’ll tell him also before he tries to blow smoke up your ass. :D

Reply

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.

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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.

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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.

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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.

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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.

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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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