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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Gary

Hello Roger,

I have a few tiles in my kitchen that have some movement to them, causing some of the grout around them to crack. I suspect the cause is due to cracked thinset. Is there a way that I can repair the thinset or otherwise reinforce it without breaking the tile? I don’t have any replacement tiles lying around and am not sure where the original installer purchased them.

Thanks,

Gary

Reply

Roger

Hi Gary,

There’s no real way to do that without removing the tile. You may be able to remove the grout and inject an epoxy into the grout line around the edges of the tile. Depending on the cause of the movement that may or may not work.

Reply

Danny

So we have a large kitchen and mudroom above a finished basement in a new construction home with 12×12 tiles. The subfloor is Oriented Strand Board with sheets of plywood on top. There is some sort of thinset on top of the plywood but I don’t know what type. While still under warrenty, within the first year, we have had to have the subcontractor come out and repair these hairline cracks in the grout lines running several tiles long and in both directions. The cracks start small and over a month start to get so bad that we are vacuuming up large chunks of grout. They are also occurring in one half of the kitchen/mudroom area, while there are also some portions of the other half that appear to be very powdery, like we can scrape them up with our fingers. We have had the subcontractor out to fix these 4 times and every time they say none of the tiles are loose and this is normal due to the house settling or too much humidity. So they grind out the cracking grout and re grout it. Then it cracks again in a few months, always in the same spots and sometimes in additional spots and we have to do the whole thing over again.

Questions:
-Are they right about the cause?
-Should we just let them continue to come out and implement the same fix indefinitely?
-Is there a way to objectively determine if a tile is loose other than their opinion?
-Do you have any recommendations about what we can do about this?

Thanks for your help,
Danny

Reply

Roger

Hi Danny,

1. No, they are not right about the cause. ‘House settling’ is bullshit in regards to tile installation unless you live in a piered house over an ocean, and humidity has nothing at all to do with cured grout. No you should not let them keep doing the same thing.

2. Yes, but it requires removing the tile to determine the coverage and bonding of the thinset to both the tile and substrate.

3. The solution depends on the cause. The lack of bond or proper coverage is one possibility, which requires removal and replacement. Since it’s in the same areas consistently I lean toward the cause being either improper substrate support for the given installation, or improper installation of the layers of substrate beneath the tile. The tiles can be well bonded to the substrate, but if the substrate is moving it’s going to crack your grout.

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Josh

We recently had 4 separate areas of tiling done in our rehab home. The kitchen, which is the largest area, already is showing micro cracks in the grout. And by micro, I mean I only noticed them when I was about a foot away. It is only happening there and not to the other areas. Also, the cracks are only happening at intersecting joints, not on the sides. The particulars are:

2×10 floor joists cross braced 16″ o.c.
3/4″ plywood (real stuff not osb)
3/8 particle board over the 3/4 (was already there from previous floor)
1/2″ durock set with thinset using 1/4″ square notched trowel
1/2″ durock then screwed down with 1-5/8″ rockon screws while thinset was still wet
All seams taped with thinset and anti – alkali tape
All tiles are 12×12 porcelain with 1/4″ lines
Used sanded Polyblend on all.

The other 3 areas all used the same color and the kitchen was a different one. I’m wondering if maybe the batch was mixed too thin and there is shrinkage? Any input would be greatly appreciated as I am looking for another professionals opinion before I contact the installer.

Thanks again.

Josh

Reply

Roger

Hi Josh,

It could be a couple of things. The first would be the fact that there is particle board beneath your backer. Particle board compresses as weight it placed upon it, then it springs back (almost). Multiple compressions lead to an indentation in the particle board. It doesn’t matter that you have thinset beneath your backer if the substrate beneath it is not solid and/or is compressible. It could also be the mixing and shrinking of the grout, polyblend is horrible in my opinion.

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Thomasina

HI, SOME OF THE GROUT IN MY BATHROOM FLOOR TILES LOOKS LIKE SOMETHING IS EATING THROUGH IT AND ITS PROTRUDING ABOVE THE GROUT LINE IN A CRUMBLE STATE. IF THIS IS SOME TYPE OF INSECT HOW DO I KILL IT? wE HAVE UNDERFLOOR HEATING AND PORCELAIN TILES WHICH WERE LAID WITH FLEXIBLE ADHESIVE AND FLEXIBLE GROUT.

Reply

Roger

Hi Thomasina,

I have no idea. It could be (literally) hundreds of different things. Unless you can identify what is ‘eating’ through your grout I can’t begin to tell you how to eliminate it.

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Carol

Hi There, I have a concern and am looking for a reasonable answer, I’m at wits end. About a year and a half ago I had my tile removed and almost my whole house retiled. The old tile had been in approx 12 years, no issues, tile was just old and we wanted to remove carpet. The job was beautiful. We have a concrete slab and tile over it. This was using regular grout from a bag. About 6 months later grout was coming out and in traffic areas looked marbled and little pits just coming out. Contractor repaired the areas and came back in 3 weeks to seal it and it looked the same again, all blotchier and marbled looking. He took the grout out of the whole house and came back with epoxy grout, it once again looked gorgeous and within 6 months it is coming out and all marbled blotchie looking again. Thin-set was the only thing that was under the tile. I know in one area where it is really bad, there is a huge crack in the floor that the previous contractor filled in prior to the tile job 12 years ago, when that tile was removed there was no sign of moisture everything was dry and powdery, i do not believe there to be a moisture problem is why i bring this up, we had no grout issues with the tile they removed just the new installed tile and grout. What would cause two different types of grout to do this? This is a reputable contractor and I do trust him but we are looking at a redo again. I did bathrooms, shower and the majority of my 2000 sq ft home and parts of it look like I did it myself and I ashamed of it. Please advise.

Reply

Roger

Hi Carol,

It sounds like there are no soft joints or perimeter joints in your installation. Pressure will build up from regular seasonal movement and cause the entire installation to expand and contract. That pressure releases at the weakest point, normally the grout. It may also be lack of complete or adequate coverage of thinset causing an incomplete bond, which allows your tile to move as it’s walked upon. Start by asking about expansion or soft joints and perimeter joints.

Reply

Carol

Hi Roger, thank you for the reply. In further investigation we are noticing the floor has several uneven tiles, tenting in areas. The grout company came out to take samples but since this is the second time with different grout, I am not expecting it to be the grout but rather the preparation of the floor as you have indicated as a possibility. Our contractor wants to do a moisture test to remove him as responsible basically as we found out that he is pretty sure that he did not reseal the crack when removing the old tile. WE see no signs of moisture and neither did they when putting down the tile. He stated that he will not do another repair without the moisture test and that if it comes back to not be moisture, he is stumped as to what could be the problem. I do see that it is butted up to the walls in most area with out any soft joints. Is it possible also that he just did not allow enough cure time? This has been ongoing for 2 years .

Reply

Roger

It is lack of expansion and perimeter joints. The pressure build-up will sheer the bond of the thinset beneath the tile. I highly doubt that it is moisture.

Reply

Christopher

My house was restumped over a year ago. Shortly after we gutted and renovated the kitchen which included new everything like subway tiled splashback and fresh plaster. We recently gutted and replaced the bathroom which includes 600x600mm floor to ceiling tiles. At the same time the tiler did the kitchen floor. After a couple of weeks the grout has started to crack and crumble mostly in traffic areas especially the shower floor. The tiler believes it’s mmovement but no signs are shown in any other room. I believe the grout has areas of shrinkage along with poor curing. What do you think?

Reply

Roger

Hi Christopher,

Did he use sanded or non-sanded grout? If non-sanded then it’s likely just shrinking rather than movement.

Reply

Christopher

The tiler said non sanded with an additive. The floor and walls were grouted on separate days and only the floor is poor. I’m finding it hard to believe it’s movement when no where else in the house is showing signs.

Reply

Lauri

Roger,
Thank you for your website. It has allowed me to ask some very pointed questions of my contractor about why my kitchen floor tile grout is cracking. I’m wondering how you would fix a tiled kitchen floor if you knew that there was no joist blocking, no thinset between the substrate and backerboard and no crack isolation membrane installed before the floor was tiled with 12″x24″ rectified porcelain tiles? My contractor’s solution is to pull and replace two tiles that have the biggest problems with cracked grout with some kind of super duper adhesive (there are other areas of cracking), then grind out all of the grout and replace it with some kind of super duper grout. I told him that if the floor is flexing, then there isn’t any grout in the world that won’t crack, but maybe I’m wrong (I really hope I’m wrong because he said the next solution would be to pull the entire floor). If he pulls the entire floor, is my only option a crack isolation membrane? We can’t get at the entire underside of the floor because there’s a finished basement beneath the kitchen. Thank you.

Reply

Roger

That is not the only solution at all. Any proper substrate which allows for the deflection ratio of your particular floor will work just fine. However, if your floor does not meet the minimum deflection requirements it will need to be properly shored up before tile is installed over it. Your contractor should know how to measure for that and compensate for it if needed. Which takes us to your first question – why would they do it if they know. They may not know.

Reply

Lauri

It’s evident that he either didn’t know or think about the deflection. What is the chance that their proposed fix for the floor will work, in your opinion? Is that what you would do if you were asked to fix this mistake?

Reply

Roger

It depends on whether it’s cracking due to an insufficient substrate or something else. I would take the whole thing out if it were mine to fix.

Reply

Patricia

Hi Roger,
In my den, the tile tented, then tile went down. Felt a bit crunchy when walked on but that’s all. This is the first time I lived in a house on cement foundation. House was recived in will, no idea who put down the floor, ws there when my son bought it a few months before he was killed at work March, 08 . I have only been in here two years. We had a pretty heafty rain as of late, the tile tented, popped now the grout is cracked, but dry. Who would you recommend I go to for help & repair? What is going on? House is all tile and I am afraid of what’s to come. Really would welcome good advice!!! Thank you.

Reply

Roger

Hi Patricia,

It would be my bet that there are no soft joints or perimeter joints in the installation. Wood (wall framing) and concrete move at different rates, soft and perimeter joints compensate for built-up pressure caused by that. When there are none, and the tile is against the walls without space, that pressure has to release somewhere, it’s normally right in the middle of an installation (as you now know). Any reputable tile contractor should be able to help you out. You may be able to have the loose ones replaced and have soft joints installed throughout the installation. That would likely solve your problem provided the entire installation is not compromised.

Reply

Mark Poggio

I just tiled a small powder room floor. The first day I tiled it and the next morning I grouted it. All was well so I thought, my friend who I did this for later that evening tried to steam clean the floor (shark steam cleaner). Later that night he calls me and says the grout started coming out and some tiles popped up. The underlayment of the floor was concrete. I think the problem was the grout was too fresh and not cured enough. He thinks it has something to do with the tile moving. Normally I would agree however, not all the tile is moving just a few, but the majority of the grout is.

Reply

Roger

Hi Mark,

It’s the grout. I have no idea why the tile came up, they obviously weren’t properly bonded to begin with. Any cementitious product requires a full 28 day cure before infusing moisture into it. Steam cleaning should not be done until it’s down and competed for a month.

Reply

Mark Poggio

That is what I thought for the grout, when I went over to choke him I looked at the tile and none were loose. However a lot of the grout was bad, I cut it out and re-grouted.

Thank you, Just wanted to reconfirm my thoughts.

Mark

Reply

Don

I just tiled my shower walls a few days ago – I used a premixed sanded grout and some of the grout is cracking. The largest seam is 1/2 inch but most are smaller. Since the grout is only a few days old – is there a way I can fix this?
Don

Reply

Roger

Hi Don,

The absolute largest grout line you can use that type of grout in is 1/4″ – and that’s pushing it. It shrinks, that’s why it shouldn’t be used there. The only proper way to fix it is to remove that grout and replace it with powdered sanded grout you mix with water.

Reply

John

Hi Roger,

I have a slab in my backyard (about 200 sq feet) that I want to tile.
Here are a few images:
http://www.wuza.net/upload/13913.jpg
http://www.wuza.net/upload/13914.jpg

It is pretty level already and there are a few cracks that I plan to fill with some cement. I am really on a budget (remodeled already half the house in the last 6 months – including tiling the kitchen on top of cement boards)

I have a few questions where your input would be greatly appreciated:

- Do you think I can tile directly on top of the slab (it doesn’t seem to move anymore – 40 years old slab) or must I use ditra (ditra would be the same price as the tile I plan to install…)?

- The edges of the slab are not straight (wavy line) and I have two choices:
– Cut the edge tiles with a diamond cutting tool with a cruved line following the slab border (my guess is that I would waste a lot of tiles…)
– Rent a concrete saw to make the slab rectangular (seems easier and would fix the wavy border that I didn’t like anyways)

Thank you for your help,
Regards,
John

Reply

Roger

Hi John,

You either need ditra or another crack isolation or uncoupling membrane. Filling those cracks with cement will not alleviate the stress point, it’s already done that. All that will do is give it something else to crack in the same area. If you don’t like the wavy get rid of the wavy. :D I would, I don’t like it either.

Reply

John

Hi Roger,

Thank you for your answer.

At the Lowes next to my place they only sell Mapei thinset. Do you recommand Modified or unmodified thinset:
- Between the concrete and ditra ?
- Between the ditra and the tile ?

Should I fill the cracks with cement first or just the thinset I put between the concrete and ditra will be enough to hold the tiles?

Thank you,
John

Reply

Roger

Unmodified for both. You should fill the cracks, but with silicone. You want to prevent thinset from getting into the cracks, it will lead to it cracking out as I described, which may lead to problems over that area.

Reply

Lynn

Hi Roger. Thank you, and the sub flooring is plywood. I’m wondering how much give it has… We’ll look into these possibilities. Again, thank you!

Reply

Lynn

Hi Roger,
My husband installed some tile and grouted it three days ago. The grout is cracking in some spots, and we do not know the cause. The tile was put down using 3/8″ of thin set, and the grout lines are a 1/4″. The grout was mixed exactly the same way he always mixes it (toothpaste consistency), and he’s never had a problem with grout cracking before. He did another room a couple weeks ago, and it has had no problem (I should note that the other room is chilly and empty, this room with the cracking is fully heated and sees lots of foot traffic). Both rooms have wooden sub flooring also… Any idea what the cause could be and how to fix it? Any input would be greatly appreciated! Thank you.

Reply

Roger

Hi Lynn,

It could be an inadequate subfloor (you didn’t mention what’s under the tile), improper type of grout (unsanded rather than sanded) or grout shrinking from too much water added.

Reply

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