How to seal a bathtub with a large gap between the tub and the floor or wall? (AVOID Doing This!)

Taking a bath after a long day can feel great. Finishing a bathroom can take quite some work though. It can be annoying to have a large gap next to a bathtub as things can fill into it. Even worse, it can lead to dangerous mold. For this reason, it is important that we get it sealed properly. Let’s take a look at some options to get this fixed.


How to seal a bathtub with a large gap between tub and the floor or wall?

Depending on the size of the gap between the tub and floor, you need to use various techniques to fill it up. Here are some of the common techniques-

Breaks up to one-fourth inch

Caulk is the best material to fill in gaps of up to one-fourth of inches. It is a flexible material that gets pushed inside the hole and fills it. After a while, the chalk dries up and creates a waterproof barrier.

If you have installed tiles on the wall next to the bathtub, you will need to select a caulk that is close to the color of the grout. Use sanded caulk to fill gaps larger than one-eighth of an inch. Use normal caulk for gaps smaller than one-eighth of an inch.

First, ensure that the gap between the bathtub and the wall is dry, and clean and there are no other items lying there. Cut the upper part of the caulk tube and squeeze out a thin bead of caulk into the gap.

Using your wet fingers, spread out the caulk smoothly and you should be done. Let it dry for a while before you take a bath. It will be necessary to redo this every few years. It is important to inspect the chalk from time to time to see if it is still properly sealing the hole.

Check out this video to get a better idea-

There are different types of chalk. Make sure that you get a big brand such as Loctide as they use qualitative materials. Cheaper chalks might not last that long. This is not something that you want to save money on as bad materials can lead to a lot of problems.

Gaps of up to half-inch

If you have a gap between your bathtub and the wall that is between one-fourth of an inch to half an inch, here is what you do. You will have to use two streaks of caulk in the gap. First, you will need to apply one streak of caulk along the side of the bathtub, and then the second layer will be touching the wall. Immerse your finger in water and join both beads properly so that it appears like one thick line.

This can be more challenging to do and you might have to ask your plumber to do this for you. Water can get in small holes so it is important that you get it done properly. Water can create damage as it builds up over time so you have to be careful when you clean the caulk so that it doesn’t get dented.

If you install the backer board properly, you can also avoid a lot of gaps around the bathtub. By moving it around slightly, you can already close some holes.

Very large gaps

If the gap is up to six inches, you will need some backer rods. Since backer rods are stretchy foam tubes, they will perfectly fit into the gap. While buying the backer rod, just check with the hardware store if it is meant for areas that get humid and moist. These rods tend to absorb water, and that is not what we are looking for.

Then insert the backer rod inside the gap and allow it to fill in the gap. Now use a streak of caulk to seal the backer rod to the bathtub from one end and the adjoining wall from the other end. There are tools that make it easier to install the backer rods but a screwdriver often works.

You can add some silicone to finish things off. This is done as we discussed before and ensures a tight seal. Check your local code to make sure that this is allowed.

You can also use a plastic water strip dam to close the gap. This can be a more durable solution. You can use a saw to cut it to size. Once again, you can use some silicone to properly seal the hole.

Most often it is better to expand the drywall or tiles so that you have a smaller gap. Backer rods can work but they are more fragile and can lead to problems over time. They are often used as a temporary solution. Backer rods also don’t look that nice and can break down after a few years. This is why most plumbers will advise that you close down the gap by adding some waterproof material. It is a common problem and plumbers want durable solutions.

If there is a hole in the drywall, you will have to patch it. This is quite easy to do and will make your bathroom look a lot better!

When you install a bathtub, it is important that the wall behind it is completely waterproof. There are tapes and sheets that allow you to keep the wall next to the bath dry at all times. Getting this right is essential. Sometimes bathrooms have to get torn down after a few years as there is water damage due to improper installation. Plumbers often get called out for this. It can be challenging to fix a bad installation without tearing things down.


So now you need not worry about how to fill the gap between the bathtub and the wall or floor. You can successfully seal the gap and use it for many more years. Enjoy the summers with some nice and relaxing baths in your favorite bathtub.

If you find that this is too hard to do, you can always ask your plumber to help you with this. If you use chalk, it is important that you use a fluent movement when you apply it. The pieces should be connected as one small hole can lead to a lot of damage and even mold.

It is annoying if there is a gap between the bath and the wall. Dirt and dust can fall into it and it doesn’t look nice. A small piece of wood and some chalk can go a long way in fixing this. Make sure to use a leveling tool and waterproof chalk.