Black Shower Sealant, Gone Overnight: The 5 Mould Gels That Actually Work in 2026
The Short Version
| Type | Price* | Active ingredient | Best for | |
|---|---|---|---|---|
| Skylarlife Gel | Gel, nozzle tube | ~£13.99 | Sodium hypochlorite | Silicone sealant, the proven pick |
| Kilrock Brush-On Gel | Gel, brush applicator, 2 x 250ml | Check current price | Hypochlorite-based | Washing machine seals, tight gaps |
| Inpumo Mould Remover Gel | Gel + brush | Check current price | Not fully published | Budget gel, with caveats |
| HG Mould Spray | Spray | ~£5-10 | Sodium hypochlorite ~3% | Flat walls, tiles, ceilings |
| Astonish Blaster | Spray | ~£2 | Sodium hypochlorite | Cheap ongoing maintenance |
Black mould on bathroom silicone is one of the most stubborn cleaning jobs in a British home. You've probably already tried a spray. It ran straight down the sealant, sat on the tiles for half an hour, and the black stain shrugged it off. That's not your fault. It's Run-Off Failure: the stain lives inside the silicone and needs hours of contact to break down, and gravity gives a spray about three minutes.
Gel is the answer, and it isn't complicated: a thick gel clings to vertical silicone, rubber door seals and grout lines for hours, which gives the active ingredient time to reach the staining under the surface. Almost every product that works here uses the same chemistry, sodium hypochlorite, which is bleach in a formulation built to stay where you put it. One note for American readers: this is the product category you'd search as "mold gel". Same stuff, one letter different.
We compared the products actually available on Amazon UK right now on ingredients, dwell time, applicator design and where each one earns its place. Here's where they land.
1. Skylarlife Mould & Mildew Stain Remover Gel: Best Overall
Skylarlife Home Mould & Mildew Stain Remover Gel, ~£13.99
Skylarlife is the gel that made this category on Amazon UK, with years of listings and a mountain of owner feedback, and Ideal Home's tester came away impressed with it on grout. It comes in a squeeze tube with a narrow nozzle, so you lay a bead directly along the silicone joint like you're applying sealant. Leave it on for several hours or overnight, wipe it away, and in most cases the black staining comes with it.
The honest bit: this is sodium hypochlorite in a thickened carrier. You are paying £13.99 for roughly the same active ingredient that costs £2 in a spray bottle. What you're actually buying is the gel format, and for stained silicone the format is the whole game. A spray physically cannot do this job. The gel can.
Pros
- Longest track record of any gel in the UK market
- Nozzle tube lays a clean bead along sealant joints
- Clings overnight without running
- Works on silicone, grout and tile joints
Cons
- Priciest option here per tube
- Strong bleach smell, ventilate well
- Won't fix silicone where mould has fully colonised through the bead
2. Kilrock Mould Remover Brush-On Gel: Best for Washing Machine Seals
Kilrock Mould Remover Brush-On Gel, 2 x 250ml with brush
Kilrock ships as two 250ml bottles with a brush applicator, and that brush is why it wins the washing machine job. A door seal isn't a flat bead of silicone, it's a folded rubber gasket with a hidden channel where the mould actually lives. A brush lets you work gel into that fold without putting your fingers in bleach. At 500ml across the pair, there is enough to do the seal, the shower and the grout behind the taps, with product left for the repeat treatment a badly stained seal usually needs.
Kilrock is an established UK household-cleaning brand, though it publishes less formulation detail than HG. The honest trade is physical: a gel thin enough to brush will slump on a long vertical run where a nozzle gel holds its bead. Pick this one when the applicator matters, which for rubber seals it does.
Pros
- Brush applicator reaches inside folded seals
- 2 x 250ml covers the seal, shower and grout
- Clings well on vertical rubber
Cons
- Thinner than a nozzle gel, slumps on long vertical runs
- Less ingredient transparency
3. Inpumo Mould Remover Gel: Budget Gel, Eyes Open
Inpumo Mould Remover Gel, 2-pack with brush
Amazon UK is flooded with near-identical import gels under names like Inpumo, Magic Extreme and UK Magic Gel, usually in multipacks at low prices. The 2-pack brush version we link is representative of the type. The gel format works the same way as the branded options, and plenty of owners get good results on grout and sink silicone.
Our caution is straightforward: these listings often publish incomplete ingredient and safety information, brand names change frequently, and quality can vary batch to batch. If you want the cheapest way to try mould gel, this is it. If you're treating a big area or you care about knowing exactly what's in the tube, spend the extra on Skylarlife or HG.
Pros
- Cheapest way into the gel format
- Usually ships with a brush
- Multipacks are a generous quantity
Cons
- Incomplete ingredient labelling on many listings
- Interchangeable brands, inconsistent quality
- Listings come and go
4. HG Mould Spray: Best for Flat Walls and Tiles
HG Mould Spray, 500ml
Not a gel, and it earns its slot anyway. HG is the most recommended mould remover in the UK, roughly 3% sodium hypochlorite with sodium hydroxide in a spray that's formulated to cling better than the £2 options. On flat surfaces, painted walls, tile faces, window reveals and ceilings, spraying beats squeezing gel out of a tube on both speed and coverage.
Use it where gravity isn't your enemy. On a vertical silicone bead it will still run off before it's finished the job, which is exactly why this site exists. Wall goes to HG, sealant goes to gel.
Pros
- The UK benchmark, consistently top of independent tests
- Fast on flat surfaces, works in about 30 minutes
- Published safety data sheet, transparent formulation
Cons
- Runs off vertical silicone like any spray
- Strong fumes, needs good ventilation
5. Astonish Mould & Mildew Blaster: Cheapest Maintenance
Astonish Mould & Mildew Blaster, 750ml, ~£2
UK-made, sodium hypochlorite based, and around £2 for 750ml. Astonish won't out-clean a gel on established sealant stains, but that's not its job. Its job is the weekly or fortnightly spray-and-wipe that stops mould re-establishing after you've done the deep clean with gel. At this price you can keep a bottle in every bathroom.
Sensible pairing for most homes: one tube of Skylarlife for the annual deep treatment, one bottle of Astonish for upkeep. Total outlay about £16.
Pros
- Around £2, hard to argue with
- UK-made with a published ingredient list
- Perfect for post-treatment maintenance
Cons
- Won't shift established stains in silicone
- Runs off vertical surfaces fast
Our Verdict
Buy the Skylarlife for stained bathroom silicone. It's the proven gel and the nozzle makes the job clean.
Buy the Kilrock for washing machine and fridge seals, where the brush applicator earns its keep. Then follow the step by step seal guide.
Add the Astonish either way. £2 of maintenance spray is what stops you needing the gel again in three months. And read the prevention guide, because no product fixes the moisture problem that grew the mould in the first place.
How We Evaluate
We compare published ingredients, safety data sheets, applicator design, dwell-time requirements and verified owner feedback. We don't accept payment for placement, and rankings don't change based on commission rates. When a product is rebranded bleach at a premium price, we say so, and we explain what you're actually paying for. Full methodology on our about page.
New to the category? Start with gel vs spray and the buying guide. If mould keeps returning or covers a large area, read when mould means a bigger problem.