How to Caulk a Bathtub Wide Gap

Learning how to caulk a bathtub wide gap goes a long way to keeping your bathroom space clean and neat. 

Caulking simply refers to applying a waterproof filler and sealant to your bathtub to prevent any leaks. Therefore, when done perfectly, you don’t have to worry about water damage or leakage that may extend to the walls.

Additionally, a tub that isn’t caulked tends to increase the susceptibility of moisture build-up and damage beyond the tub, all the way to the tiles or walls.

While it may seem like a tough and painstaking job, caulking your bathtub is pretty easy when you learn the right techniques. So, to help you save a buck on calling a plumber, we’ve shared a simple DIY technique.

3 Reasons to Seal Bathtub Wide Gaps Immediately

Before you start to work your tub, it’s always a good idea to understand why exactly you need to do so. 

Doing so allows you to do your job with better precision and key results in mind. So, let’s look at the three common reasons why it’s important to fix big gap with caulk in your bathtub;

1. Preventing Water Damage & Leakage

The most obvious reason for sealing a tub wide gap is to prevent the risk of leakage and ultimately, water damage.

If left unfixed for long periods, the gap in your tub can lead to extensive leakages.

The leakage extends further to cause damage to the tub, wall, and even tiles. Leakage can be caused directly by water dripping or moisture build-up on the gap between tub and wall.

2. Unpleasant Smells & Odor

Another reason why you want to fix your bathtub’s wide gaps is to prevent the increased smell and odor build-up.

Cracks on the tub can cause different elements to penetrate and even build up around the holes. This can be anything from soap scum, grime, and even pee.

Over time, the build-up begins to develop an unpleasant smell and odor that can only be fixed by a complete revamp of the tub.

3. Bacteria Build Up

In addition to odor, caulking huge gaps in bathtubs can lead to bacteria build-up.

Ever noticed slimy substances building up around the tub with a light reddish, orange color finish? This is not ordinary scum that results from soap build-up.

Instead, it is a bacteria mold that can very easily cause infections such as UTIs. To get rid of this mold, you will have to give it a good dose of bleach and scrub it with a brush (you will probably want to dispose of it after).

The next step should be to fix those cracks and gaps in your tub!

How to Caulk a Bathtub Wide Gap

Tools Required

  • Caulk softener
  • Old cloth or tarp (to cover the entire tub)
  • Putty or utility knife (plastic razor blade for plastic tubs)
  • N-abrasive pad or rag
  • Mineral spirit
  • Dry rag or paper towel
  • Blue painter’s tape
  • Caulk application gun

Step 1: Getting Rid Of Old Caulk

If you have an abrasion-free tub (non-plastic tub), you can apply commercially available caulk remover to weaken the caulk before prying it out. However, you may also have to remove the caulk manually if the remover isn’t strong enough.

You can never put in new caulk without removing the old one first. Start by covering the tub with a tarp or drop cloth so you can protect it from staining and scratches. Next, use a putty or utility knife to pry off the old caulk off the tub.

However, if you have a plastic-covered tub, you are better off using a plastic razor blade to prevent scratches.

Not all the caulk will come off, but, try to do as much of a precision job. With very little old caulk left over, there shouldn’t be an issue when putting on new caulk.

To make it easier to add the new caulk, you want to clean the tub after removing the old caulk.

Step 2: Cleaning the Tub

To clean out your tub, use a non-abrasive pad or rag to gently scrub out the remaining residue on the tub.

If you notice a thicker old caulk residue, soak the rag in a mineral spirit and use it to gently dissolve the caulk.

Once done, wipe the tub dry with a dry rag or paper towel and let it rest for a few minutes to completely dry out.

After drying out, you will begin to enter the actual caulking process. But first, you want to cover the wall to protect it.

Step 3: Covering the Wall

Tape the wall using painter’s tape – kept in parallel layout at least 3/8 of an inch apart and then proceed to apply the caulk.

Step 4: Applying the Caulk

This step involves using a gun to caulk your bathtub gaps. Start by trimming the nozzle of the gun at the tip at a 45-degree angle to expose a 3/16 inch hole (approximately).

Holding the gun at a 45-degree angle, begin to apply steady pressure to the gun’s trigger as you move, applying the caulk.

Maintain the moving speed to apply an equal amount of caulk, ensuring you fill a large gap between tub and wall as well. Moving too fast will lead to a thin application while moving too slow may over-apply the caulk.

When you are done applying the caulk, you have to smoothen it out to ensure proper application.

Step 5: Smoothing Out the Caulk

This final step seals the caulk’s application. To effectively caulk large gaps around the tub, use a dampened lint-free rag to press the caulk into the joints, applying pressure using your fingers.

As you fill the caulk into the gaps, continue to pull and move it gently to ensure each gap is covered thoroughly.

Once done, remove the painter’s tape, one strip at a time, avoiding touching the fresh caulk. After removing the tape, adjust the caulk filling with your fingers one more time, to ensure you fully cover even the smallest gaps and crevices.

Next, let the caulk dry out and cure for at least 24 to 48 hours before you resume using the tub.

Also Read: How to Install a Bathtub on a Concrete Floor

How to Seal 1 Inch Gap between Tub and Tile?

Tools Needed

  • Caulk softener
  • Old cloth or tarp (to cover the entire tub)
  • Putty or utility knife (plastic razor blade for plastic tubs)
  • Non-abrasive pad or rag
  • Mineral spirit
  • Dry rag or paper towel
  • Blue painter’s tape
  • Water and moisture-proof backer rod
  • Caulk shaping tool or applicator

Step 1: Removing the Old Caulk and Clean Out the Tub

Use commercially available caulk cleaner to weaken the old caulk and pry it out (follow the instructions on the caulk remover’s packaging). If there are still remnants of the caulk, use a putty knife or utility knife to manually pry it out.

Next, use a nonabrasive pad or rag (soaked in mineral spirit) to clean out the tub after removing the caulk. Let the tub dry out completely, then, apply painter’s tape to the wall.

Step 2: Preparing the Area

To help you control the amount of caulk you apply, set up a backer rod before you start the application process.  Go for a waterproof backer rod to prevent moisture or water absorption.

To apply in the gaps, push the rod down into the gaps to fill it completely. The next step is to caulk large gaps around the tub and tiles.

Step 3: Applying Caulk

Use a shaping tool or caulk applicator to apply the caulk into the gaps. Before you apply the caulk around the gaps, test and give you an idea of the application.

Next, squeeze in a bead of caulk on each side of the backer rod placed in the gaps exactly where the rod joins the tub and wall to seal the space.

Examine all the freshly sealed gaps to ensure there aren’t any extra crevices or small holes left.

When you are satisfied with filling the 1-inch gap between tub and tile, let the tub and wall dry out for at least 24 to 48 hours before you resume using the tub.

How to Caulk Gaps Less Than 1/8 Inch?

Sometimes, caulking bathtub wide gaps may not be the task at hand. Even smaller gaps of less than a quarter of an inch still require sealing to prevent leakage, water damage, smells, and even bacteria.

Tools Needed

  • Caulk softener
  • Old cloth or tarp (to cover the entire tub)
  • Putty or utility knife (plastic razor blade for plastic tubs)
  • Non-abrasive pad or rag
  • Mineral spirit
  • Dry rag or paper towel
  • Blue painter’s tape
  • Caulk tube
  • Clean rug

Step 1: Removing Old Caulk and Clean the Tub

Start by cleaning out the old caulk using a commercially available caulk cleaner. Next, remove any remnants manually using a utility knife or putty knife.

Once done, clean ou the tub using a rag or pad soaked in mineral spirit. When you are satisfied with the clean-out, let the tub air dry completely. Then, cover the wall with painter’s tape.

Step 2: Choosing the Caulk and Clean Out the Gaps

Before you choose your caulk, examine the bathroom interior design. If you have tiles on the wall near or adjoining the tub, you want to use a caulk that matches the color of the grout between the tiles.

However, some people choose any regular caulk for gaps less than 1/8 of an inch since they believe the color isn’t that noticeable.

Before the application, the gaps have to be squeaky clean. So, use a clean lint-free rag to wipe the gaps.

After cleaning out the gaps of any residues or dirt, you can proceed with the caulk application.

Step 3: Applying the Caulk

Cut out the tip of the caulk’s tube and begin to dispense a small bead of caulk into the gap, steady moving along until it is thoroughly filled. When down, wet your fingers (to prevent the caulk from sticking) and smoothen it out to fill the gaps.

When done, examine each gap to ensure the job is done with precision.

Once done, let the freshly filled gaps dry out and the caulk mature for at least 24 hours before using the tub.


Caulking your bathtub yourself offers a great way to save money on your household repair and maintenance fund.

Even a small gap, can make the difference between a clean, neat tub from that riddled with leaks, water damage, bad odor, and bacterial mold.

Therefore, when you know the proper solution, you can effortlessly evade these issues.

After all, no matter the size of gaps, the process is pretty much the same, i.e. affordable and with a very small list of tools needed.