Bathroom sealant
How to silicone a bath
Siliconing a bath properly takes patience, but the result is a watertight, mould-free seal that lasts for years. The single most important preparation step is filling the bath with water before you apply any sealant, so the seal stretches to fit the loaded weight rather than splitting when the bath is used.
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Step-by-step guide
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Fill the bath with water first
Before touching the old sealant, run cold water into the bath until it is full. This loads the bath to its normal in-use weight and pushes it down to its lowest position. If you apply sealant to an empty bath, the gap will widen when the bath is used and the sealant will split. Leave the water in throughout the job.
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Remove all the old sealant
Use a sealant remover tool or a Stanley knife to cut away the old silicone. Work carefully along both edges — the bath rim and the wall tiles or panel — and pull it away in strips. Take your time: any old sealant left behind will stop the new bead sticking properly and will show through the finished joint.
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Clean the joint thoroughly
Wipe down both surfaces with a cloth dampened in white spirit or methylated spirit to remove grease, soap scum, and any residue from the old sealant. Allow the surfaces to dry completely. If you see any black mould staining on the tile or bath rim, treat it with a mould-killer spray and rinse clean before proceeding.
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Apply masking tape on both sides
Run a strip of low-tack masking tape along the wall just above where the sealant will sit, and another strip along the bath rim just below. Leave a consistent gap between the two tapes — around 6 to 8 mm is usually right. The tape keeps the sealant lines clean and gives you a neat, professional finish.
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Cut the nozzle and apply a continuous bead
Cut the nozzle of the silicone cartridge at a 45-degree angle. Use a sanitary or bathroom-grade silicone — not a general-purpose one — as it contains fungicide to resist mould. Load the cartridge into a gun and apply a smooth, even bead along the full length of the joint without stopping. Keep the gun moving at a steady pace.
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Smooth the bead with a wet finger
Wet your fingertip with cold water and run it firmly along the bead in a single smooth stroke, pressing the sealant into the joint. Wetting your finger prevents the silicone sticking to your skin. Work quickly before the sealant starts to skin. Remove excess silicone with a damp cloth as you go.
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Remove the masking tape immediately
While the sealant is still wet, pull the masking tape away from both sides in one clean movement. Pull each strip back on itself at a low angle rather than lifting straight up, and do this immediately after smoothing — do not wait for the silicone to skin or the tape will lift the bead with it.
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Leave to cure before emptying the bath
Allow the sealant to cure for at least 24 hours before removing the water or using the bath. Most bathroom silicones are fully cured in 24 to 48 hours at normal room temperature. Read the manufacturer's instructions on the cartridge for the specific curing time. Keep the bathroom ventilated during curing.
Tips and common mistakes
- Always fill the bath before siliconing — this is the most common mistake and the main reason bath sealant splits early.
- Use sanitary silicone with antifungal additives, not standard clear or white silicone, or mould will return quickly.
- Do not rush the surface preparation — the sealant will only bond to a clean, dry, grease-free surface.
- One smooth pass with a wet finger gives a better finish than multiple attempts, which smear the silicone.
- Pull the masking tape while the silicone is still wet for clean edges; once it starts to skin, it will tear.
- If the joint is wide or uneven, a sealant smoother or profiling tool gives a more consistent result than a finger.
Not confident about this job? Ask Richard at The Sandwich Handyman — bath siliconing is a small, tidy job that can be done in a single visit.