When there is a significant amount of movement on the substrate of a tiled floor or wall it may lead to grout cracking. When this happens it will leave what looks like a crack in the grout where it has come away from the tile. Unless your grout was installed very recently this is always due to movement in the tile. If your grout is new it may be caused by incorrectly mixed grout. With grout that has been doing this for a while it may lead to whole chunks of grout coming loose and leaving large voids in your grout lines.
While it may be tempting to simply mix up some more grout and fill these voids you need to know that it will not last. If you do this it will fill the grout lines just like new but over time will lead to the same problem. Grout over grout is not a permanent solution.
Why it won’t last
The first reason is that when you go over the top of grout that is already cured with new grout, there is no adhesion to the old grout. It will instead simply create a layer of grout on top of the old grout. These layers have no way of sticking to each other. When you grout tile the grout actually sticks to the sides of the tile rather than whatever substrate is beneath it. While it will stick to the substrate at the bottom of the grout lines to an extent, it is not a permanent bond. Attempting to grout over the top of old grout is simply stacking two seperate layers of grout. It will always remain two seperate layers.
The second reason is no matter how much of the old grout you may take out to install new, if you do not fix the actual reason the grout failed in the first place, eventually the same thing will happen again. As with any problem you may encounter with a tile installation, you must figure out the initial cause and fix it to prevent repeated problems. This is an involved process which I will cover in a different article. For now I’ll stick with the solution for the grout problem.
What to do
Rather than simply filling the grout line where the grout is missing, you must remove the old grout at least 2/3 the depth of the tile so the new grout has a feasible surface to grab onto. The easiest way to do this is with a grout saw. Ideally you would remove the old grout all the way to the substrate before regrouting it, but 2/3 will be sufficient if it is difficult to remove.
You need to remove any of the old grout that seems loose or has come loose from the sides of the tile. You also need to make sure the spot where the new grout butts against the old is a 90 degree angle, or close to it. In other words from the top of the grout line straight down. You do not want a slope. Eventually a slope must be feathered to a very thin edge. That will be the first place it will fail again, any very thin layer. A 90 degree angle prevents that.
It is also better to make the transition from old grout to new in the middle of a grout line rather than at one of the corners of the tile. The grout line at the corner of the tile has six different spots it can fail, the middle of a grout line has only one. It lessens the chance of failure.
After you remove the sufficient amount of the old grout just mix some new grout and fill the lines. You must make sure you force the new grout into the grout lines very well. You want to make certain there are no voids and the lines are full.
The above method will work to temporarily fix your cracking grout. As I pointed out above, you must find the initial reason for the grout failure before a permanent fix will last. It’s difficult to say how long this fix will work, it may be two weeks, it may last a year. That depends on the severity of the problem that caused it. It also depends on the application (wall or floor) and how much use it gets. A floor in your main entryway will not last as long as a shower that is never used.
You should also take into consideration the age of the grout. If you are repairing grout that has been installed for five years, the new grout, even if it is the same brand and color, will not likely match perfectly. The best solution, of course, would be to fix the cause of the cracking and regrout the entire floor. Depending on what you’re fixing and why this method may solve your problem.
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Roger,
We have a 40 year old terra cotta tile floor that was set into the foundation of the addition to our 1862 farmhouse. The floor of course settled and the tiles cracked and are uneven. The grout doesn’t come up to top of tiles so it is a bit rough and also uneven. It is dark gray in traffic areas (due to dirt, etc.) and light grey in non traffic areas. I am wondering if they didn’t even grout but just pushed the tiles into the concrete? Could we re-grout over that to make the grout more even with the tiles?
Thanks so much for taking the time to answer us…also, any good solutions for removing self-stick vinyl tile adhesive from the terra cotta tiles?
~Carla
Hi Carla,
Old-school tile setters, especially with terra cotta, would simply use the setting mortar as the grout also. That’s likely what you have. If you want to regrout it you’ll need to scrape out 2/3 the depth of the tile first. Grout bonds to the sides of the tile, not what’s underneath it. You need to give it something to bond to.
Get some denatured alcohol and a spray bottle and spray the adhesive, let it soak, then spray it again and scrub with a white scrub pad, vacuum it up. If there’s any left just repeat. That’s normally how I get old adhesive off.
Thanks for your quick response Roger. We decided to paint the floor instead. What tips do we need to keep in mind when doing that?
Paint the floor??? I don’t have any idea, I don’t paint floors.
If you’re painting over the tile I know there are special kits you can use to do so, but I don’t know anything about them, never used them.
Hey, I just bought a home with a newly renovated bathroom. The tile/grout are separating at the corner (90 degree wall-to-wall). Can I just fill the gap with caulk?
Hi Craig,
You can, but it won’t last – so no.
You need to scrape the grout out of there first – then it’ll last.
Hi we have recently had our kitchen floor tiled but have noticed that on some of the tiles the grout is cracking, we don’t want to do the whole floor again, any ways of getting around it?
Hi Nasima,
Well, you can regrout. But if your grout is cracking it is due to movement of some sort. Which means your floor was not properly prepared for the tile, some facet of it was installed incorrectly or there is not proper movement accommodation for the tile. That means that it will eventually crack again, and will continue to do so until the underlying problem is remedied.
Love your site! And your reason for starting it. Had to like you on FB. I guess your jackassedness got me subliminally for me to have chosen that word. :o)
Take Care,
Helga
Sigh, Pebble Floor in shower. My first time doing this…and I removed too much grout between some of the pebbles, creating little buckets which will hold water. I know I can’t grout over grout. But, is it feasible to use a silicone grout over the sanded grout?
Much appreciated!
Hi Helga,
No such thing as silicone grout. Not sure what you plan on using?
Hi There, thank you for taking the time. :o)
This particular one I have here is made by MAPEI and has a label saying “Keracaulk Sanded” then Siliconized Acrylic Caulk. OH! So, there you go, it’s not grout, it’s caulk, made to match the colors of the grout they sell……and I had to do this over the net. I’m usually satisfied just making a jack ass out of myself at Lowes..
I make a jackass of myself EVERYWHERE! Hell, it’s even at the top of my website.
No worries.
Hi. Last night I just finished replacing my bathroom linoleum floor with ceramic penny tiles. I have two problems. The most distressing to me is that a roughly six inch section of grout did not dry to match the color of the rest of the floor. For whatever reason the grout did not lighten as it dried. It is of course right in the center of the room. Please tell me that there is some way to lighten this without digging it out. My second concern is that in a few places there are what look like pinholes in the grout. I assume there were air bubbles that worked their way up during drying. Do these pinholes need to be filled in with grout or will sealant seal these up? In case it matters I used unsanded Mapei Keracolor grout in pale gray. Thanks for your help.
Hi Michelle,
Unsanded grout will have pinholes if you aren’t extremely careful with it. It’s a pain in the ass. Sealer will fill it, but you’ll still see it. The discoloration may lighten up over time. Unsanded is more dense than sanded and may retain moisture longer. It could take a couple of weeks. Do not seal it until it lightens. If it does not lighten you either have vapor dissipation under that area (doubtful if in the center of the floor) or it may actually be the rest of the grout that is lighter than it should be?
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