Sunken Grout Lines (Causes, Prevention Methods & How To Fix)

Most people assume that grout is only used to make tiles look better. Though true to some extent, grout also reinforces the joints between tiles while preventing them from cracking on the edges or moving from their initial position.

Due to these benefits, grout is a must-use product in any tile installation project. Most of the time, grout is installed without any problems. However, sometimes, the grout may start to sink as it dries.

If you have recently discovered sunken grout lines, here is a comprehensive guide on what causes this problem and how you can fix it.

Grouting tiles seams with a rubber trowel

What are Sunken Grout Lines?

This is when the grout between your tiles is too low to the point that it’s visible and you can feel the gaps under your feet (when you walk on the floor barefoot). In any tile installation job, the grout needs to adequately fill the gaps to the point it’s on the same level as the tile’s surface.

However, if it’s too low, then you are dealing with sunken grout lines. This problem is very easy to diagnose. Because all you have to do is observe.

What Causes Sunken Grout Lines?

• Grout Mixture Problems

I will never stop emphasizing the importance of following manufacturer instructions. Grout should be mixed to a cake-like consistency and then applied to the joints between tiles.

When it’s in such consistency, the grout may be a bit difficult to push into the gaps. Some DIY folk prefers to add more water to make it easier to spread. But in doing so, the grout ends up shrinking as it dries resulting in sunken grout lines.

Incorrect mixtures are the leading cause of sunken grout lines. When the grout mixture is too wet, most of that water will evaporate when the grout dries and you will end up with low lines on your tile joints.

• Air Gaps in the Joints

The presence of air gaps on tile joints can also cause sunken grout lines. You may not realize that there are air gaps when installing grout because they will be concealed by the paste.

However, as the grout dries, the air gaps below escape slowly thus pushing the grout lower into the joint. This is a factor that you need to keep a close eye on.

• Wiping the Tiles Too Early

Understandably, laying tile is a pretty tiresome job. Therefore, you may be in a hurry to clean off the grout stains on your tiles. However, if you wipe the tiles too early, you may remove some of the grout from the joints.

How to Prevent Sunken Grout Lines?

• Follow the Recommended Mixing Ratio or Use Premixed Grout

If you always find yourself adding too much water to grout when mixing it, you need to put a stop to this habit. Otherwise, all your grout lines will always be sunken. Follow the manufacturer’s recommendation regarding the mixture ratio.

Don’t forget to always give the grout enough time to sit. This allows the chemicals to bond better with one another.

Alternatively, if mixing grout seems challenging, you can opt for premixed grout. This type of grout can be used straight from the packaging. You don’t have to deal with ratios or anything. It’s a much better choice for newbies.

• Give the Grout Enough Time to Set Before Wiping It Off

No matter how quickly you want to finish up this job, you should always give the grout enough time to settle before you start cleaning the tiles with a wet sponge.

Experts recommend that you wait at least thirty minutes before you can start wiping. Avoid being too vigorous when cleaning as that can also contribute to the removal of grout on tile joints.

A pro tip you can use is to clean tiles with a moderately wet sponge. Too much water will make it easier for you to scoop off some grout from the lines. Excess water can also weaken the grout making it easier to wash off.

• Push the Grout Deeper into the Joint

When installing grout, you shouldn’t just apply it over the surface and move on to the next tile. Make sure that you push it deeper into the gap. Doing so will ensure the removal of any air gaps that may later lead to sunken grout lines.

How Do You Fix Sunken Grout Lines?

Now that you know the causes and how to prevent them, let’s discuss how you can fix sunken grout lines.

There is one common misconception out there about sunken grout joints. Many people assume that you can just add more grout over it and you would be done. But this approach may lead to adhesion problems between the new grout and the old grout.

The best method of fixing this problem is by grabbing a putty knife and removing all the old grout. Then re-grouting while following the tips I shared with you earlier.

It may seem like a lot of work but this ensures a flawless and long-lasting finish. If you are struggling with removing old grout, denatured alcohol always does an excellent job of getting rid of any stubborn residue.

If you installed the sunken grout a few days ago, there is a shortcut you can use. Because the grout is relatively fresh, you can wet it down with water and then add new grout over it.

When the grout is wet, it’s much easier to adhere to new grout than compared to when it’s wet.

Why Can’t I Just Add New Grout Over Sunken Grout Lines?

The first thing that usually comes to mind when you spot sunken grout lines is to mix up a new batch and pour it over. However, this is not advisable because the new grout will not last.

As mentioned above, the new grout can’t adhere to the old grout. As tempting as it may be, refrain from pouring a new grout mixture over an old one as it will not bond. Follow the approach I have shared in the above sub-topic.

Grouting ceramic tiles. Tilers filling the space between tiles using a rubber trowel.

How Can You Create Sunken Grout Joints?

As absurd as this may sound, there are certain situations when you may be asked to sink the grout by a few millimeters.

This mostly applies to contractors and tile installers working for clients interested in showing off their tiles or simply wanting a unique design.

Whatever the reason, the best way to create sunken grout joints is to install tile as you usually do. And then as the grout starts to cure, grab a scouring pad and rub it over the grout lines until you achieve the desired height.

Alternatively, you can mix the grout with excess water so that it shrinks to a lower level when it cures.

Do Grout Lines Sink Eventually?

Like all other construction products, grout is also susceptible to wear, especially as time goes by. Grout doesn’t last forever.

The more traffic your tiles are exposed to, the more grout will wash off. So, eventually, there is a huge chance that you may end up with sunken lines.

However, the problem we are talking about in this article is that sunken lines appear days or weeks after installation.

This usually indicates there was a problem with the mixture or installation and needs to be fixed asap because sunken grout lines can make your floors look unsightly.

This problem can also affect comfort because you will always feel the gaps in the joints as you walk over the floor.

How to Remove Sunken Grout?

If you have decided to re-grout your tiles, you will need to remove the sunken grout and there are several ways you can go about this process. You can use a utility knife or a screwdriver.

These tools do a marvelous job of removing fresh grout. Adding some water can also soften the grout. But if it’s too stubborn, the best tool to use is a grout saw. This machine can plow through the toughest grout lines. It also speeds up the process.

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