Quick answer: Slice along both edges of the old sealant with a utility knife, then peel away as much as possible by hand. Use a plastic sealant remover tool, not a metal blade, on acrylic baths and shower trays to avoid scratching the surface. For stubborn residue, apply a sealant removal gel and leave it for at least two hours, then wipe the surface clean with isopropyl alcohol before applying new sealant.
Old bathroom sealant rarely fails gracefully. It discolours, grows mould, cracks, and eventually shrinks away from the surface, letting water get exactly where it shouldn’t. Removing it properly before applying anything new isn’t optional either, since fresh sealant won’t bond well over old, degraded material.
Why Sealant Needs Replacing
Sealant has a genuine lifespan, and it varies depending on where it’s used. Shower and bathtub sealant typically lasts three to five years, kitchen backsplash sealant around five to ten years, and exterior window or door sealant five to ten years or longer depending on weather exposure. Regardless of age, sealant should be replaced once it shows cracking, peeling, discolouration, or a loss of proper adhesion, since these signs mean water can already be getting behind it.
A Critical Warning: Know Your Surface
This is the step that catches people out most often. Metal blades can easily scratch acrylic baths, plastic shower trays, and similar surfaces, so always use a plastic razor blade or a purpose-made plastic sealant removal tool on these materials rather than a standard utility knife or metal scraper.
What You Will Need
- A utility knife (metal blade for tile/ceramic, plastic blade for acrylic/plastic surfaces)
- A plastic sealant removal tool
- Sealant removal gel, for stubborn residue
- Isopropyl alcohol or white spirit
- Rubber gloves
- Paper towels or a lint-free cloth
Step 1: Score and Peel
- Run the utility knife along both edges of the sealant bead, cutting through where it meets the tile or surface on each side.
- Take hold of a loose edge and peel the sealant away by hand. With luck, it will come away in long, satisfying strips.
- Work in short, sharp strokes rather than long dragging cuts, which gives more control and reduces the risk of slipping and scratching the surface.
Step 2: Scrape Away Remaining Material
- Hold your sealant remover tool or plastic scraper at a shallow angle against the surface to avoid gouging or scratching.
- Work along the full length of the joint, removing any sealant left behind after peeling.
- For tight corners where a scraper or your fingers won’t fit, carefully use the tip of the utility knife instead.
Step 3: Use Sealant Removal Gel for Stubborn Residue
If old, hardened sealant won’t come away easily, or you’re dealing with sealant that’s been there for many years, a gel-based remover does much of the hard work for you.
- Apply the gel directly onto the remaining sealant using a sealant gun, cutting the nozzle at a 45-degree angle first for a controlled bead.
- Leave it to work for at least two hours, though very old or thick sealant may need twelve hours or more to break down properly.
- Once softened, the sealant should scrape or peel away far more easily than before.
- You can either apply the gel before scraping to soften everything from the start, or scrape off what you can by hand first and use the gel only on the stubborn leftover bits.
Step 4: Deal With Leftover Residue
- Dab a small amount of white spirit onto a cloth and rub it over any remaining bits of silicone, which softens the residue and makes it easier to wipe away.
- Pick off any stubborn small chunks with pliers, tweezers, or an old toothbrush.
- Continue until the surface feels smooth to the touch, with no lumps or ridges remaining.
Step 5: Clean the Surface Thoroughly
Once all the old sealant is gone, wipe the entire joint with isopropyl alcohol on a clean cloth. This step matters more than it might seem, since any leftover residue, oil, or moisture will stop new sealant bonding properly, leading to premature failure of your fresh seal.
Why Black Mould Appears on Sealant
Black discolouration on bathroom sealant is almost always mould or mildew, encouraged by poor ventilation, ongoing moisture, and the natural ageing of the sealant material. If mould has been a recurring problem, it’s worth improving bathroom ventilation, either with an extractor fan or by opening a window regularly, alongside your resealing job, otherwise the new sealant will likely face the same issue over time.
Choosing a Replacement Sealant
Once the surface is clean and dry, choose a 100% silicone, mould-resistant sealant specifically designed for bathroom use, which offers the best combination of flexibility, durability, and water resistance for wet areas like showers, baths, and sinks.
Related Guides
- How to Remove Mould from Silicone Sealant (if cleaning is enough and you don’t need to replace it)
- How to Clean a Shower Screen
Frequently Asked Questions
Can removing old caulk damage an acrylic bath or shower tray?
Yes, if you use a metal blade or scraper. Always switch to a plastic razor blade or plastic sealant removal tool on acrylic and plastic surfaces to avoid permanent scratching.
How long does bathroom sealant usually last before it needs replacing?
Shower and bathtub sealant typically lasts three to five years, though this varies with ventilation, usage, and the quality of the original application.
Do you need to remove all old sealant before applying new?
Yes, in almost all cases. New sealant applied over old, degraded material won’t bond properly and is likely to fail again quickly. The main exception is certain refresh-specific products designed to bond directly over 100% silicone, but standard sealant needs a fully clean, bare surface.
What causes black mould to grow in bathroom sealant?
Poor ventilation, ongoing moisture from showers and baths, and the natural ageing of the sealant material together create ideal conditions for mould and mildew to take hold along the joint.
Final Thoughts
Removing old sealant is genuinely straightforward once you match your tools to your surface, using a plastic blade on acrylic and a metal one on tile, and take the time to fully clean the joint before resealing. Rushing this step, or leaving old residue behind, is the most common reason a fresh reseal fails within months rather than lasting years.