Filling Grout Lines with More Grout

by Roger

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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I seem to have removed too much grout when cleaning and it seems low in most areas. The grout is not even 24 hours on the floor. Can I add more at this stage? At what point is it too late?



Hi Ben,

You should be able to now, you need to dig it out after about three-four days.



Firstly, I want to thank you for such a wealth of information on tiling!!! We built our 6ftx4ft walk in shower ourselves from the studs up and couldn’t have done it without your instructions. I read dozens of other sites and their “how to” instructions leave out critical steps. We scrupulously followed your instructions for building the shower pan with deck mud and rubber membrane. I also built my curb with your tip of using the stucco mix over the lath which worked great! So now that I have tooted your proverbial horn, please don’t scold me for what I am about to ask. We tiled the shower floor with a carrera (or Chinese similar) polished stone small square tile and used unsanded grout as that gout spaces were small enough to allow. What I have failed to do was seal my tile and grout. I was spreading grout 48 hours before my inlaws arrived and wouldn’t let them shower their 1st day so the grout set for 3 full days. I figured that after a week of showering and hand drying the tiles immediately after that I could seal the tiles and grout after everyone left. Well as life goes for an ADD procrastinator like me….. I still haven’t sealed the tile and it has been being used for 3 months. The grout seems to be receding with use and cleaning or is this just my imagination because I haven’t sealed it? There are no cracks in the grout, but it seems like the grout is too low between the tile. Is there anything I can do other than dig out perfectly good grout to add too it? Is my best option to just seal it now and deal with it?



Hi Marissa,

Your best option is likely to just clean it well and seal it now. I honestly don’t know why it would seem to be getting lower after three months, it won’t do that so it may just be the edges of the tiles getting a bit dirty, which enhances the outline of the grout lines – knowwhatImean? If you want to add more grout you’ll need to dig the existing grout down to 2/3 the depth of the tile.



We just had our shower and tile around our tub replaced a month ago by I thought a good company. Well the grout is cracking along the bath tub and I just noticed a vertical line in the shower corner beginning to crack. Also the grout around the shower pan is chipping away. We haven t finished payment yet. What do I need them to do to fix this problem



Hi Leslie,

You need to have them remove the grout along the tub (where the tile meets the tub) and in the corners (where one wall meets the other wall) and replace it with silicone. Any change of plane requires a flexible sealant. Silicone can compensate for differential movement in changes of plane, grout will not (which you already know).



Hi! I have a 10 year old travertine shower and it looks like there is caulk over the grout in the corners and the wall to floor. Needless to say, black mold has formed and I cannot get it clean.

I want to redo it, and am willing to do the work to make it right, but I am not sure what to do. Do I sand it out and regrout? Do I caulk over the grout? What type of caulk? Or grout?

Please help!



Hi Lisa,

Everything in the corner needs to be removed, caulk and grout, and replaced with 100% silicone. Most grout manufacturers have silicone which matches their grout color, so you should be able to find one that is fairly close to your grout color.


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