Mould-resistant sealing — homes & washrooms
Anti-Mould Sealant in Chathamblack joints cut out, treatedand sealed to stay white
Cleaning black sealant buys you a fortnight. Cutting it out, killing what is underneath and resealing in a fungicidal product buys you years — and takes a single visit to your bathroom or washroom.
Free quotes, photo pricing on small jobs, and a straight answer about the ventilation issue if that is what is driving the mould.
£2m cover
public liability insurance
CITB & CSCS
accredited on site
RAMS on request
for commercial jobs
Free quotes
photo quotes on small jobs
Chatham based
Kent, London & South East
The service
What this work involves
— and who it is for
What anti-mould sealing involves
Anti-mould sealing is the replacement of mould-affected joints with sanitary-grade silicone that carries fungicide within the cured film. It applies wherever water and warmth sit together: bath and shower joints, wet-room perimeters, tiled internal corners, basin and WC junctions, kitchen worktop and sink lines, and commercial washroom, shower-block and changing-room joints.
The important part is that it is not just a product swap. Mould in a joint has usually colonised the sealant and the substrate behind it, so we cut the bead out in full, treat the substrate to kill the colony, let the joint dry properly, and only then apply the mould-resistant sealant. Skip the treatment and the new white bead is being colonised from beneath before it has finished curing.
Who it is for
Homeowners in Chatham and across Kent whose bathroom sealant goes black no matter how often they scrub it, and landlords who need bathrooms to present properly at every check-in and inspection.
Commercially: washrooms, shower blocks, changing rooms, staff and student facilities, gyms, salons and commercial kitchens — anywhere joints are used constantly, ventilated poorly and cleaned aggressively. Bathrooms and kitchens are not automatically domestic jobs, and we handle both to the same finish.
When it is needed
As soon as black or pink staining appears in the sealant and does not come out with cleaning; when spotting reappears within days of a deep clean; when the bead has softened; or when there is a musty smell in a bathroom that is otherwise clean.
It is also worth specifying anti-mould products proactively — on any new bathroom, wet room or washroom, and particularly in internal rooms with only mechanical extraction, in high-occupancy family bathrooms, and in commercial facilities where showers run all day.
Why professional treatment matters
Mould is a living colony, not a stain. Its hyphae penetrate the sealant and can be established in grout, board and plaster behind it. Bleach removes the pigment on the surface, which is why cleaning appears to work and then does not — the colour is back within a fortnight because the organism never left.
Getting a lasting result means removing the contaminated material completely, treating the substrate, controlling moisture before sealing, and using a genuine sanitary-grade fungicidal product rather than a general-purpose silicone with 'bathroom' on the label. It also means being honest about ventilation: if a room has no working extraction and no openable window, sealant can only slow the problem down, and you deserve to be told that at the quote stage.
What it costs to leave it
A failed seal never
stays a small problem
Mould in a joint is a symptom of water sitting where it should not, and it rarely stays confined to the bead. It is also the fastest way to make a well-finished bathroom feel unhygienic, and in a rented or commercial property it becomes other people's problem to complain about.
Water damage behind the joint
The same moisture feeding the mould is soaking board, plaster and timber behind the tile. Left long enough, resealing turns into replacing floor decks, boards and ceilings below.
Health complaints and tenancy disputes
Visible mould in a bathroom generates complaints from tenants, staff and building users, and in rented property it can escalate into a formal disrepair issue.
Spread beyond the sealant
Once established, mould moves into grout lines, silicone at adjacent junctions and painted surfaces. Treating one joint late costs more than treating the room early.
Mistakes we get called out to fix
- Bleaching black sealant repeatedly instead of replacing it — the pigment lifts, the colony stays.
- Applying new white silicone straight over a mould-affected joint without treating the substrate.
- Using general-purpose silicone with no fungicide in an unventilated bathroom or wet room.
- Resealing while the joint is still damp, giving the new bead poor adhesion and a wet start.
- Sealing over grout that is itself contaminated, so mould reappears at the edge of the new bead within weeks.
How a job runs
The order of work,
start to finish
- 01
Photos or inspection
Send photos of the affected joints and the room. We identify how far the mould has spread and whether ventilation is a contributing factor.
- 02
Free written quote
A fixed price for removal, treatment and resealing, with the mould-resistant product named and any grout issues flagged.
- 03
Full removal
The contaminated bead is cut out from both faces and residue scraped and wiped, so nothing colonised remains in the joint.
- 04
Treatment & drying
The substrate is treated to kill the colony, then the joint is allowed to dry properly before any new sealant is applied.
- 05
Reseal & aftercare advice
Fungicidal sanitary-grade sealant applied and tooled, curing time explained, and practical advice given on ventilation and cleaning products.
What you get
The difference a properly
detailed finish makes
White joints that stay white
Fungicide held in the cured film resists recolonisation, so the bead does not start spotting again within weeks.
The colony removed, not covered
Treating the substrate after full removal deals with the organism rather than sealing it in behind fresh silicone.
A bathroom that feels clean
No black shadow line along the bath or tray — the single detail that makes a bathroom read as neglected.
Water kept out of the fabric
A sound, correctly sized joint stops the moisture that feeds mould from reaching boards, plaster and joists.
Honest advice on ventilation
If extraction is the real problem, we tell you, so you are not paying for the same reseal every year.
One visit, fixed price
Most domestic anti-mould reseals are a few hours' work, priced from photos before we arrive.
In detail
Materials, methods
and the variations we cover
Products: what makes a sealant mould-resistant
Sanitary-grade silicones from Mapei, Illbruck, CT1 and Arbo include fungicidal additives held within the cured film, which suppress mould growth on and just under the surface for years rather than weeks. They also cure to a denser, less porous surface than general-purpose products, giving spores less to grip and making the joint easier to wipe clean.
That performance is not indefinite and it is not magic. Fungicide is consumed slowly over the life of the joint, and a bead permanently wetted in a room with no ventilation will eventually stain regardless of product. In chlorinated environments — pools, spas and leisure wet zones — the product changes again to a chlorine-resistant sealant, because pool chemistry attacks standard sanitary silicone. Where a bead needs to be both mould-resistant and colour-matched to dark grout, that is available too.
Method: removal, treatment and moisture control
The contaminated bead is cut from both joint faces with blades, the bulk removed and the residual film scraped and solvent-wiped so no colonised silicone remains. Where mould has reached grout, board or plaster behind the joint, the substrate is treated with an appropriate biocidal wash and allowed to work rather than simply wiped over. Contaminated grout at the joint edge is flagged: if the grout itself is colonised, resealing alone will not stop staining reappearing at the bead margin.
Then the joint is dried. This is the step most often skipped and the one that decides whether the reseal lasts — a joint that has been wet for years holds moisture in the substrate, and silicone applied onto it will not achieve full adhesion. Once dry, the new bead is applied in a continuous pass and tooled to a concave profile that sheds water instead of holding a film of it, which is itself part of keeping the joint mould-free. We finish by telling you the curing period plainly: keep the joint dry, usually overnight and ideally a full day.
Where anti-mould sealant is used
Bath to tile and bath to panel joints. Shower trays, low-profile trays and wet-room formers. Shower enclosures, screens and glass panels. Tiled internal corners and change-of-plane joints. Basins, pedestals, WC pans and cisterns. Kitchen worktops, splashbacks, sinks and hobs. Utility rooms and laundry areas. Commercial washrooms, shower blocks and changing rooms. Gym and studio wet areas, salon backwash units, and staff and student facilities. Commercial kitchen and food-preparation junctions where hygiene standards apply.
It is also the right specification for any bathroom without an openable window, any internal shower room relying solely on mechanical extraction, and any family bathroom in constant use — the three environments where general-purpose silicone discolours fastest.
Domestic and commercial differences
Domestically, this is a fast, high-impact job: one visit, dust sheets down, the room handed back clean, and a bathroom that instantly looks looked-after. Photo quoting means you get the price before anyone visits. We will also tell you the unglamorous truth about extraction, drying towels in the room and running the fan for longer after showers, because those habits determine how long the new joint stays white.
In commercial washrooms and changing facilities the joints see many times the use and much harsher cleaning chemicals, so mould-resistant products are the default rather than an upgrade. Work is phased so facilities stay partly open, RAMS are issued on request, and we hold CITB and CSCS accreditation and £2 million public liability cover for site access.
Questions
What customers ask
before booking
- How much does anti-mould resealing cost?
- Quoted individually and free of charge. Bathrooms are usually priced from photographs, so you get a fixed figure without waiting in for a visit. We do not publish 'from' prices because joint length and removal difficulty vary widely.
- Why does my sealant go black even though I clean it?
- Because the mould is inside the sealant and often in the substrate behind it. Cleaning removes the pigment, not the organism, so the colour returns. Full removal, treatment and resealing in a fungicidal product is the only lasting fix.
- How long will it stay white?
- In a reasonably ventilated bathroom with a properly prepared joint, years. In a room with no working extraction and constant moisture, less — which is why we are upfront about ventilation. We do not advertise a guarantee, so we give you realistic expectations instead.
- How long does the work take?
- A typical bathroom is a few hours. If the substrate needs treating and drying, we may need to allow drying time, and we will tell you at quote stage whether that means a longer single visit or a return.
- When can I use the shower afterwards?
- Keep the joint dry for the product's cure period — as a rule, overnight and ideally 24 hours. Using the shower too early is the most common cause of a premature failure.
- Do I need to fix my extractor fan as well?
- If the room cannot clear moisture, sealant is managing a symptom. We will tell you honestly if we think ventilation is the driver; the fan work itself is an electrician's job, not ours.
- Can you treat mould in the grout too?
- We treat the substrate at the joint and will tell you if the grout itself is colonised. Full grout replacement or regrouting is tiling work, and we will say so rather than seal over it and let the staining reappear.
- Is anti-mould sealant available in colours?
- Yes — mould-resistant products come in a range of shades, so a joint against dark grout or a stone worktop can be both fungicidal and colour matched.
- Do you do commercial washrooms and changing rooms?
- Yes, regularly — washrooms, shower blocks, changing facilities, gyms and commercial kitchens, phased so the facility stays usable, with RAMS on request and £2m public liability cover.
- Which areas do you cover?
- Kent, London and the South East from Chatham, including Maidstone, Sevenoaks, Tunbridge Wells, Kings Hill, Meopham, Whitstable, Tenterden, Bexley and the City of London.
Related sealant services
- Bathroom, wet room & kitchen sealing
Clean, watertight beads around baths, showers, trays and worktops — for homes in Chatham and for commercial washrooms alike.
- Sealant replacement — removal & reseal
Old, split or blackened sealant cut out completely, substrate prepped and treated, then resealed properly.
- Swimming pool & leisure sealant
Chlorine-resistant products for pool surrounds, changing areas and wet leisure environments.
- Colour-matched silicone sealant
Beads matched to grout, frames, stone or cladding so the joint disappears into the finish instead of framing it.
- All sealant services
Where we work
Based at The Historic Dockyard in Chatham, covering Kent, London and the South East — including Sevenoaks, Tunbridge Wells, Maidstone, Kings Hill, Tenterden, Whitstable and City of London.
Stop scrubbing it — have the sealant replaced properly
Send us a photo of the blackened sealant and get a free fixed price back. Removal, treatment and a fungicidal reseal, usually in a single visit.
£2m public liability cover · CITB & CSCS accredited · RAMS on request · Mon–Sat, 7am–7pm · Sunday closed