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.

{ 607 comments… add one }

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.

  • Audra Segal

    I have spots, small spots of black mold appearing on the grout of my shower floor. I have taken a butter knife & gently scraped it away, thoroughly cleaned the shower & when dry, applied grout sealer. I apply the grout sealer every other month after cleaning & am still having problems…I need help. There are no cracks in the grout anywhere & there is Provaflex lining all around the entire shower under all the tile.

  • Carol

    First grout job was perfect. Hard as concrete and nice, thick grout lines almost flush with the tile. Wrong color was applied though.

    Second grout job was the correct color, but too much water was added, so grains of sand and color were coming off on the rag when I would clean it. I noticed this installer, though he added too much water, DID remove as much of the old grout as possible. 90 degree angles, no sloped-in ditches. Old grout removed clean like slices of pizza.

    Third grout job? Well, I’m hoping it’s like cement, like the first job was. He just finished today, so I won’t know for a little. My worries… (1) I don’t think he removed enough of the old grout depth-wise, definitely not the amount the second guy did who had it down almost to the subfloor, just like if the tile had just been laid. (2) There were edges of old grout that were ‘sloped in’ and not sliced straight down along the tile like you’d slice a pizza, so maybe only 1/4 or 1/3 of the grout was removed against the uppermost edges of the tile before it began its inevitable slope. In some areas there was still old grout against the tile edges at the very top even. Those areas will be thin and weak, from the sound of it, and the first to crack. (3) Some lines of grout seem too low, too deep. They are very noticeable. (4) He chipped a tile. (5) Also found what looks like slipped grout, probably because he didn’t take the range out of the kitchen as I’d suggested. So he was moving the feet of the range over areas that hadn’t cured enough to do that.

    Needless to say, I’m very worried. Tomorrow I wipe the haze off the tile and get some moisture into the grout. He explained how to do that.

  • Tami Martinson

    Our new floor has standard spacing and deep grout lines so that I catch the edge of tiles while walking through the room! The tiles are sharp edged instead of beveled. Should they have been put down closer together or should the contractor have, at least, left more grout in the spaces?

  • robert boyko

    i use a officechair instead of a wheelchair but my grout lines are deep enough to where my wheels get cuaght in the grout lines and i have to ush myslf harder when i run into them which is quite often is there a compound like i was thinking durham’s rock hard water putty

    • Roger

      Hi Robert,

      If your wheels are getting ‘caught’ then your grout lines are HUGE. There is no product to put over existing grout to make it flush with your floor. A hard plastic mat for beneath your office chair is unfortunately your best alternative.