How To Seal A Bath

Refresh your bath's sealant and ensure it's watertight with our step-by-step guide to sealing a bath.
Written By: Richard Morgan | Updated:
How To Seal A Bath
Richard Morgan/DIY Works

Unless you have a freestanding or curved bath, your bath is likely to be installed against a wall and require sealing. Failing to do so can result in water flowing over the edges and seeping into your walls as well as underneath the tub. As you can imagine, this can eventually lead to mould, flooding, and even rotting of timber if left untreated for a long period.

Therefore, sealing your bath is essential and highly advised before using it. Luckily, it’s relatively straightforward to do and certainly something that anyone can achieve with ease, but it’s crucial that you do it correctly to avoid any complications.

Whether you are resealing an existing bath or sealing a brand new bath, below we walk you through the entire process with pictures and videos of each step.

What You’ll Need

  • Bathroom silicone sealant
  • Caulking gun
  • Utility knife
  • Masking tape
  • Paper towels
  • Sealant applicator (optional)

How To Seal A Bath

1. Thoroughly Clean The Bathtub & The Wall

Before you begin to seal a bath, it’s always advised that you thoroughly clean the edges beforehand. Even if it’s a brand-new bathtub, you’ll be surprised to see the amount of dirt that comes away from it. It’s also advised that you clean the wall where the bathtub is being sealed and ensure it’s dried thoroughly.

Although you could skip this step, it provides you with peace of mind that there will be no issues with mould growth and imperfect lines in the future.

2. Fill The Bath With Water

The next step is to fill the bath with water because this increases the weight of the bathtub. The reason why this is an important step is that the extra weight of a filled bath may increase the gap between the bathtub and the wall. Therefore, if you were to skip this step, the sealant may crack or peel away from the bathtub when it’s next filled with water.

3. Apply Masking Tape Around The Edges

In preparation for sealing a bath, you’ll want to apply two lines of masking tape around the edge of the bath and the wall. You’ll want to leave a small gap between the two lines for the sealant to adhere to the bath and wall. The size of the gap is a matter of personal preference, but 6 to 12 mm is a good guideline to follow.

Application of the masking tape around the edges is a crucial task in sealing a bath because it ensures there are straight edges and there is no excess sealant left behind. Therefore, we highly recommend taking your time to ensure the gap is consistent between the two lines of masking tape.

how to seal around a bath

Richard Morgan/DIY Works

4. Setup The Caulking Gun & Sealant

With the bath ready for sealing, you’ll want to set up the sealant ready for application. To begin, you’ll need a suitable caulking gun that’s in good working order and, of course, your sealant. Considering that most sealants are relatively affordable, we always recommend spending slightly more for the best-rated bathroom sealant you can find.

Once you have the sealant and caulking gun to hand, insert the tube into the gun and then use a utility knife to cut the tip off the sealant ready for sealing. Ideally, you’ll want to cut around 2 to 3 cm down the nozzle and at a 45-degree angle. This type of cut will make it slightly easier to apply the sealant at an angle along the edge of the bathtub.

5. Apply The Sealant

With all the preparation work finished, you can then begin to seal the bath by starting at the furthest corner so that you don’t have to go back on yourself.

It’s recommended that you start at this corner because it’ll make the application go far more smoothly as you make your way around the edges of the bath.

Whilst applying the sealant, you’ll want to keep the gap between the nozzle and bath very close (as shown in the photo) and gently squeeze the trigger of the caulking gun. It’s worth pointing out that the sealant may not come out of the nozzle straight away, and you may need to squeeze the trigger a few times before it starts to come out.

Ideally, you’ll want to follow the line in one continuous motion, but if you need to stop, try not to go over any sealant that’s already been applied.

how to seal a bathtub

Richard Morgan/DIY Works

6. Remove Excess Sealant

After you’ve applied the sealant, you may notice that the finish is uneven and a bit lumpy (as shown in the photo above). However, this is to be expected and to finish up the job of sealing a bath, you’ll need to use your finger or a dedicated sealant applicator for a smooth finish.

We personally prefer to use a wet finger, and we run it across the edge of the bath at an angle to smooth and shape the sealant (as shown in the photo). However, if you have an applicator, you can do the exact same, but it’s not an essential tool required for sealing a bath.

As you smooth and shape the applied sealant with your finger or applicator, you may collect excess sealant. Therefore, it’s advised that you have a paper towel to hand to wipe it clear because it can be very sticky.

sealing a bath

Richard Morgan/DIY Works

7. Remove The Masking Tape & Analyse The Results

Once you have smoothed and shaped the sealant upon the bath, you can proceed to remove the masking tape. After peeling it away, you should be left with a sealed bath with straight edges. Although you may be tempted to have a relaxing bath after your hard work, it’s advised that you wait at least 24 hours so that it can completely cure.

Below are some videos that we filmed and posted on our YouTube channel for this guide to sealing a bath.

Sealing Baths With Large Gaps

If you need to seal a bath with large gaps, there are extra steps that’ll be required for it to be completely waterproof. The large gaps are mostly due to poor installation or an uneven wall, but you can still seal large gaps with a few extra steps.

If possible, reinstalling the bathtub closer to the wall is the best solution to the problem. However, this isn’t always possible, and it can also be a time-consuming and costly task. Therefore, you can either fill the gap with a bonding material and adhesive or use flexible caulking strips.


Hopefully, our guide on how to seal a bath has given you the confidence to give it a go yourself. Unless you have to deal with sealing a bath with large gaps, it really is a straightforward task that only requires basic tools. However, if you feel that you need further help or information, feel free to get in touch, and we will try to assist where possible.

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