The sealant around a bath is one of the hardest-working parts of the room. It sits at the junction between the bath and the wall, flexing every time the bath is filled and emptied, and constantly exposed to water, soap, and steam. Over time it cracks, discolours, or develops mould that no amount of cleaning will shift. Resealing is a straightforward job that costs very little and makes a significant difference to both the appearance and the waterproofing of the room.
Why does bath sealant need replacing?
Bath sealant fails for predictable reasons. Understanding them helps you apply the new sealant correctly and extend its lifespan:
-
Movement. A full bath holds a significant volume of water. The weight causes the bath to flex slightly, which, over time, works on the sealant joint. Rigid sealant or incorrectly applied sealant cracks under this repeated movement. This is why the type of sealant matters and why filling the bath before applying is not optional.
-
Mould. Bathrooms are humid environments, and the sealant joint is one of the most persistently damp spots in the room. Once mould takes hold beneath or within the sealant, it cannot be cleaned out; the sealant must be removed and replaced.
-
Age and UV exposure. Silicone sealant yellows and becomes brittle with age. Even well-maintained sealant in a frequently used bathroom typically needs to be replaced every 2-5 years.
-
Poor original application. Sealant applied to a damp surface, without first filling the bath, or in thin or uneven beads, will fail faster than correctly applied sealant.
Related: How to Remove Bathroom Mould
How often should you reseal a bath?
Every 1-2 years for a heavily used family bathroom. Every 2-5 years for a less frequently used bath in good condition. The practical trigger is not the calendar but the condition of the sealant itself.
Signs it is time to reseal your bath
-
Visible cracks or gaps in the sealant bead
-
Black or dark grey mould growth that does not clean off
-
Sealant that has pulled away from the wall or the bath edge
-
Yellowing or hardening of the silicone
-
Water pooling in areas it should not reach
If any of these are present, reseal promptly. Water that gets behind failed sealant travels into the wall structure and beneath the bath, causing damage to plasterboard, joists, and flooring that is expensive to repair.
If the sealant on your bath has failed due to the bath itself ageing or being damaged, it may be time to consider a replacement. Browse our full range of baths, including freestanding baths and shower baths across all sizes.
Related: Different Types of Baths
What you need to reseal a bath
Materials:
-
Sanitary silicone sealant that is waterproof and mould resistant. Use a product specifically labelled for bathrooms. Do not use decorators' caulk or general-purpose silicone, which are not formulated for constant water exposure.
-
Masking tape (low-tack)
-
White spirit or isopropyl alcohol
-
Washing-up liquid
Tools:
-
Sealant gun (caulking gun)
-
Sealant removal tool or utility knife
-
Flat-head screwdriver or plastic scraper
-
Silicone smoothing tool (or a teaspoon will do)
-
Cleaning cloths and kitchen roll
-
Protective gloves
On sealant choice: sanitary silicone is flexible, waterproof, and contains a fungicide to slow mould growth. It is the correct product for this job. It comes in white, clear, and grey to match different tile and bath combinations. White is the standard choice for most baths. If your tiles or bath surround are grey or dark, clear silicone is worth considering for a less visible finish.
Related: What Accessories Do I Need to Buy Along With a Bath?
How to seal a bath
Once you’ve got all the materials, here’s a step-by-step guide to sealing a new bath or resealing your bathtub:
Step 1: Remove all the old sealant
This is the most time-consuming part of the job and the one most people rush. If any old sealant remains, the new sealant will not bond correctly and will fail faster. Do it properly.
Score along the edges. Use a utility knife or sealant removal tool to score along both edges of the sealant bead on the bath surface and on the tile or wall surface. Hold the blade as flat as possible to avoid scratching the bath.
Remove the bulk. Work the blade or a flat-head screwdriver underneath the sealant bead and peel or lift it away. Old sealant usually comes away in strips once you get underneath it.
Remove the residue. Fine strands and thin layers of silicone will remain on both surfaces after the main bead is removed. Rub these away with your fingers or use a dedicated silicone remover product. White spirit on a cloth removes stubborn residue on the bath surface. Use a plastic scraper rather than a metal one on acrylic baths, metal will scratch.
Do not leave any residue. Run your finger along both surfaces. If you can feel any silicone at all, it needs to come off before the next step.
Step 2: Clean and dry the surfaces thoroughly
New silicone will not bond to a dirty, greasy, or damp surface. This step directly determines how long the new sealant lasts.
-
Wipe both surfaces down with a cloth dampened with white spirit or isopropyl alcohol. This removes soap scum, limescale, body oils, and any silicone remover residue.
-
Wipe again with a clean dry cloth.
-
Leave both surfaces to air dry for at least 30 minutes. Do not rush this step. The surfaces must be completely dry before you apply sealant.
-
Run your finger along both edges one final time. They should feel clean and slightly tacky from the cleaning agent. No moisture, no residue.
Related: How to Clean a Bath
Step 3: Fill the bath with water
This is the step most commonly skipped and the one that causes the most sealant failures. Do not skip it.
Fill the bath with water to two-thirds to three-quarters full. The weight of the water causes the bath to flex downward slightly and pushes it gently away from the wall at the joint. If you apply sealant with an empty bath and then fill it, the movement can break or stretch the new sealant. Applying the sealant with a weighted bath means it cures in the correct position for the way the bath will be used.
Leave the bath full throughout the entire process and only empty after the sealant has fully cured, following the next steps.
Step 4: Apply masking tape
Masking tape is not strictly necessary, but it significantly improves the neatness of the finished joint. It takes a few minutes to apply, but it saves considerably more time on cleanup.
Apply a strip of low-tack masking tape along the wall or tiles, parallel to the joint and approximately 3–5mm from the edge of the gap. Apply a second strip along the bath surface, again approximately 3–5mm from the edge of the gap. The gap between the two pieces of tape is where the sealant bead will sit.
Work from the back corner (furthest from the door) forwards. Press the tape down firmly along its length so that the sealant cannot bleed under it.
Step 5: Apply the sealant
Load the sealant cartridge into the sealant gun. Cut the nozzle tip at a 45-degree angle. Start with a small opening, as you can always cut it larger, but a nozzle cut too wide produces a bead that is difficult to control. The opening should be slightly narrower than the gap you are filling.
Starting in the back corner, apply a continuous, steady bead of sealant along the full length of the joint in one smooth movement. Keep the gun at a 45-degree angle to the joint and maintain steady, even pressure on the trigger throughout.
Work from back to front so you are always moving toward you rather than leaning over fresh sealant. For a bath surrounded by three walls, start at the back wall and work in a C-motion around to the front.
If the bead is uneven in places, do not attempt to add more sealant on top as you will create ridges that are harder to smooth. The smoothing step corrects minor unevenness.
Step 6: Smooth the sealant
You have a limited working time before silicone begins to skin, typically 10–15 minutes, depending on the product and temperature. Do not leave the smoothing until all the sealant is applied. Work in sections if the bath has multiple sides.
-
Prepare the smoothing tool. Dip a silicone smoothing tool or a teaspoon into a small bowl of water with a drop of washing-up liquid. The soapy water prevents the tool from sticking to the silicone, allowing it to glide smoothly.
-
Smooth in one pass. Draw the smoothing tool along the bead in a single continuous stroke from one end to the other, maintaining a consistent angle and pressure. The tool should press the silicone into the joint and leave a neat concave profile that slopes back toward the bath, encouraging water to run back into the bath rather than sitting on the joint.
-
Wipe excess silicone from the tool as you go.
-
Remove the masking tape immediately. While the sealant is still wet, peel the masking tape away at a 45-degree angle. Pull it back on itself, not upward. If you leave the tape until the sealant has begun to skin, it will tear the edge of the sealant bead when you remove it.
Step 7: Allow to cure
Leave the bath full of water and the sealant undisturbed for at least 24 hours. Some sanitary silicones require 48 hours for full cure, so check the product instructions.
Do not touch the sealant, run water near it, or use the bath during the curing period. Moisture interferes with the curing process and can prevent the sealant from bonding fully.
Once fully cured, empty the bath. Run your finger along the joint. It should feel firm and slightly flexible. Press gently; there should be no give or separation from either surface.
How to deal with a large gap between the bath and wall
If the gap between the bath edge and the wall is wider than around 5mm, standard sealant will not bridge it effectively and may sag or fall away.
-
Option 1: Re-seat the bath. The cleanest solution is to move the bath slightly closer to the wall. This is a job for a plumber or bathroom fitter rather than a DIY repair, as the bath will need to be disconnected and repositioned.
-
Option 2: Fill the gap first. Fill the larger gap with a backing rod (a foam rope available from builders' merchants), pressing it into the gap before applying sealant over the top. The backing rod provides the silicone with something to bridge against, reducing the depth of the joint.
-
Option 3: Caulking strips. Self-adhesive flexible caulking strips can bridge larger gaps without a sealant gun. Cut to length, peel the backing, and press firmly into place. Less durable than silicone, but a practical solution for difficult gaps.
How to reseal a shower tray
The process for resealing a shower tray is identical to the bath, with one additional consideration: shower trays often flex more than baths when stood on, particularly acrylic or resin trays. Use a flexible sanitary silicone, specifically formulated for flexible joints. Standard silicone will crack when trays are moved repeatedly.
Check the shower tray for movement before resealing. Press down on the tray with your foot. If it flexes noticeably, also check that the tray is correctly supported underneath. An unsupported tray in the centre will flex excessively and quickly break the new sealant, regardless of how carefully it is applied.
Common resealing mistakes to avoid
-
Not filling the bath first. The single most common cause of new sealant cracking is within weeks of application. Always fill the bath before applying.
-
Applying sealant to a damp surface. Silicone will not bond to moisture. The surface must be completely dry before any sealant is applied, even if it looks dry to the eye.
-
Leaving old sealant residue. Any silicone residue left on either surface prevents the new sealant from bonding. Remove every trace before starting.
-
Using the wrong product. Decorators' caulk, general-purpose silicone, and frame sealants are not suitable for bath joints. Only use sanitary silicone specifically formulated for bathroom applications.
-
Removing the masking tape after the sealant has skinned. Tape left until the sealant is partially cured, or the edge of the bead tears. Remove it while the silicone is still wet.
-
Rushing the cure time. Using the bath before the sealant has fully cured breaks the bond before it has set. 24 hours is the minimum. 48 hours is better.
Resealing or sealing a bath FAQs
How long does bath sealant take to dry?
Most sanitary silicone sealants skin within 10–15 minutes and are touch-dry within a few hours. Full cure, the point at which the sealant reaches its full strength and waterproofing properties, takes 24 to 48 hours. Do not use the bath until fully cured.
Can I apply new sealant over old sealant?
No. Applying new silicone over old silicone is one of the most common mistakes in bathroom maintenance. The new sealant bonds to the old rather than to the bath and wall surfaces, and will fail quickly. Remove all old sealant completely before resealing.
What is the best sealant for a bath?
Sanitary silicone sealant, specifically formulated for bathrooms. It should be waterproof, mold-resistant, and flexible. Do not use decorators' caulk, acrylic sealant, or general-purpose silicone for bath joints, as these are not suitable for the constant water exposure and joint movement involved.
Why does my bath sealant keep going mouldy?
Mould in bathroom sealant is caused by persistent moisture in the joint. The contributing factors are inadequate ventilation, sealant applied to a damp surface, or a sealant that does not contain a fungicide. Improving bathroom ventilation (an upgraded extractor fan helps significantly), using a mould-resistant sanitary silicone, and wiping the joint dry after each bath or shower all help extend the mould-free lifespan of the sealant.
Related: How to Clean a Bathroom
Do I need to fill the bath before resealing?
Yes. Fill the bath two-thirds to three-quarters full before applying sealant and keep it full until the sealant has fully cured. The weight of the water flexes the bath into the position it will be in when used. If you seal an empty bath, the movement when it is filled will crack or stretch the new sealant.
Need any help on sealing a bath?
Resealing a bath is one of the most straightforward bathroom maintenance jobs you can do yourself. The materials cost very little, the process takes a couple of hours of active work plus 24 hours of curing time, and the result protects the room's structure from water damage that would be far more expensive to address. Done correctly, a well-applied bead of sanitary silicone will last 2-5 years before needing attention again.
Need any advice? Visit our Birmingham showroom in Tyseley, call us on 0121 753 0700 or book a consultation to speak with our expert team.