How to caulk a bathtub – easy steps to DIY success

Knowing how to caulk a bathtub is essential for both homeowners and renters, because when the caulk between the bathtub and tile breaks down, it doesn’t just look unsightly, but moisture and dirt can get in. 

Happily, getting it back on sparkling form by reapplying the caulk is a simple DIY job – as simple, for example, as grouting tiles, which you may need to do at the same time if you are completely revamping your bathroom. 

Below, we take you through the steps of caulking a bathtub.

How to caulk a bathtub

To caulk a bathtub is similar to caulking a shower or indeed caulking baseboards. All you need do is get a few basic tools together and tell the family the tub will be out of action for a couple of days. 

You will need: 

• Utility knife or box cutter
• Razor scraper
• Tweezers or needle nosed pliers
• Clean cloths
• Methylated spirit (denatured alcohol)
• Bleach solution 
• Painter’s tape
• Sealant remover
• Non-abrasive pad
• Bathroom caulk (silicone) and cartridge gun
• Sealant remover and smoother tools
• Protective gloves and goggles

1. Remove old bathtub caulk

Put the stopper or plug in the tub to avoid bits of old sealant getting into the drain. With your gloves and goggles on, use the utility knife or box cutter to cut away the old caulk, angling the knife so that you won’t cut into and damage the bathtub. A razor scraper would help, too, and use tweezers or pliers to pick off any bits that are stuck. 

Alternatively, put on protective gloves and apply a sealant remover, following the pack instructions. You may have to wait three hours for the remover to do its job. 

‘Ideally, you’ll want to use a specialist sealant removing tool to scrape the old sealant away, which prevents any damage to the bath surface,’ says Beth Pearce, Manager for Construction and Internal Building at B&Q.    

Once you’ve got rid of the bulk of the caulk, there may still be a few tricky bits that are stuck fast. If they won’t come off easily, try softening them by applying more sealant remover and scraping with the smoother tool. A non-abrasive pad should get rid of the remainder, but take care to avoid using scratching a plastic bath. Instead, try rubbing with a cloth dipped in denatured alcohol (methylated spirits). 

2. Clean the caulking area for good adhesion

If you spot any signs of mould or mildew, mix a little bleach into some water and apply on a cloth. Rinse and leave to dry. Now wipe down the surface with denatured alcohol on a cloth. To ensure you can apply the sealant neatly, stick a strip of painters’ tape to the bath edge and another to the tiles, leaving just a narrow gap where the caulk should sit. If the bathtub is plastic, its position may flex a little when it’s full.

‘We recommend filling the bath with water first to weigh it down before you apply the caulk,’ says Beth Pearce. ‘After you’ve finished, leave the bath full of water until it has dried.’

3. Apply caulk to the bathtub

Take the sealant cartridge and cut off the end. Next cut the tip of the nozzle at a 45-degree angle. Don’t trim too much or the caulk bead will be too wide. Screw the nozzle to the cartridge and place it the gun. Squeeze the handles until you see the sealant coming into the nozzle. 

With the nozzle positioned at the end of the bath, start to caulk, keeping even pressure on the trigger as you run the sealant along the gap. Next, run the smoothing tool along the seam for a smooth finish. Remove the painters’ tape. Check the pack instructions to see how long to leave the caulk to cure. 

What is the best caulk to use on a bathtub?

Be sure to buy caulk that’s specifically designed for bathrooms rather than standard decorators’ caulk. Look out for silicone bathroom caulk, which is flexible and creates a seal that’s moisture proof.

How long does it take to caulk a bathtub?

Applying the new caulk is simple and quick. But removing the old caulk can take a while, especially if you have to painstakingly pick off old bits of caulk. And if you’re using a caulk remover, you’ll need to factor in a couple of hours for it to do its job. Don’t forget that the new caulk can take a couple of days to cure, so the bathtub won’t be ready to use immediately.