Sealing a bath with silicone to get a watertight finish

Sealing a bath with silicone and a caulk gun next to brown tiles
(Image credit: Getty Images)

No-one wants water dripping through the ceiling so sealing a bath is crucial to keeping it watertight and stopping any unwanted issues elsewhere. To make sure that this happens you will need to choose the right silicone. Look for a sanitary or anti-mould sealant that's specifically tailored for such a job.

You will also need a caulking gun to apply the silicone, and remember you will need to smooth and shape the silicone quickly. This isn’t a job you can leave for half an hour and come back to. You need to sort the silicone almost as soon as it is applied.  

Sealing a bath: A step-by-step guide 

1. Clean the area
Start by brushing away any debris or dust with a stiff hand brush. Then get a vacuum and hoover up any remaining dust or debris. Wash the areas where the silicone is to be applied with sugar soap. Rinse, dry and leave for 10 minutes.

2. Mask bath and tiles
Place a length of the masking tape – blue painters' tape is good – either side of where the silicone is to go. Leave a gap of around 3mm on both sides. Make the gap bigger if needed. 

3. Sort your silicone
Cut the silicone nozzle at 45 degrees around 5-20mm down the nozzle with a sharp knife. It's best to start small and then go larger if required. Put the cartridge in a caulking gun and squeeze the trigger until you get a tight fit.
Place a length of the masking tape – blue painters tape is good – either side of where the silicone is to go. Leave a gap of around 3mm on both sides. Make the gap bigger if needed. 

4. Prepare your silicone
Place the gun at a shallow angle – starting in one corner – and squeeze the trigger of the caulking gun. Start moving along the edge as soon as the silicone appears. You need to use a consistent speed and pressure to get an even bead of silicone. Have a practice if unsure or new to siliconing. 

5. Smooth your silicone
How long does silicone take to dry? It dries very quickly so you will need to smooth out within 10 minutes. Get a damp sponge and start in one corner. Press the sponge gently on the silicone and drag along, not stopping until you get to the end. Wipe the excess in a cloth. Repeat if necessary.

Alternatively, use a finishing tool to get an even finish. These offer different shapes so you can mould the silicone into a shape that suits your bathroom style. Wet the silicone with a fine spray before using the finishing tool.  

What do you clean before siliconing? 

Before you apply any new best bathroom sealant you need to make sure that all surfaces that the silicone is going to be applied to are clean and dry. Whether you have new or old tiles and bath, both need to be free from soap scum, shampoo and debris.

Get a solution of sugar soap and a cloth – or a kitchen scourer for stubborn stains – and wash down the tiles and bath. When finished, wash down with a fresh cloth and clean water — or spray with a showerhead to get rid of any sugar soap residue. Get a dry cloth, wipe dry and then leave to dry completely.   

How long do you leave water in the bath after sealing? 

A sealant is typically touch dry within 15 to 20 minutes but it takes a lot longer to fully dry — or cure as it is known. This takes around five to six hours for a quick drying sealant or around 24 hours for a standard silicone sealant. Ideally you want to leave the water in the bath for 24 hours to get the best finish.

If you are siliconing a shower or sink, you won’t need to fill the shower tray or the sink before sealing. Both these will be installed on solid surfaces and will have much less water in them compared to a bath.  

How do you remove old sealant? 

If you are resealing your bath you will need to get rid of the old sealant before you can think about applying any new sealant.

There are a few options for removing silicone or caulk. The simple option is to use a sharp Stanley knife and some serious elbow grease. Alternatively, you can invest in a silicone removal kit that has all the tools needed for quick and easy removal. 

Once removed remember to clean up any left over sealant residue to get ready to apply the new silicone.  

Old caulk being removed in bathroom with caulk removal tool

(Image credit: Getty Images)
Steve Jenkins

Steve is Homebuilding & Renovating's DIY content editor, and has been a writer and editor for two decades. He is an avid DIYer with over 20 years of experience in transforming and renovating homes. He specialises in painting and decorating, but has strong all-round building skills, having previously worked in the industry for 10 years.