Mould Gel vs Mould Spray: The Only Comparison That Matters Is Contact Time
Here's the thing the product labels won't tell you: gels and sprays are mostly the same chemical. Sodium hypochlorite, household bleach, does the killing and the stain removal in Skylarlife's £14 gel, HG's £8 spray and Astonish's £2 spray alike. If the chemistry is identical, why does the gel clear blackened shower sealant while the sprays fail at it year after year?
Contact time. That's the entire answer, and it's why we call the spray problem Run-Off Failure: the product leaves the surface before the work is done.
The physics of a vertical surface
Mould staining in silicone isn't a surface film. The organism grows into the sealant and leaves pigment beneath the surface, and hypochlorite needs prolonged contact, hours, not minutes, to penetrate and break that pigment down. Now spray a thin liquid onto a vertical bead of silicone. Watch it. Within two or three minutes gravity has pulled nearly all of it down onto the tray or the tiles. The stain got a couple of minutes of weak contact and needed a couple of hundred. You can repeat that every Saturday forever and the sealant stays black.
A gel is the same active ingredient with the viscosity turned up until gravity loses. Lay a bead of gel on that same silicone and it's still sitting there eight hours later, wet, in full contact. Same chemical, a hundred times the working time. That's the whole trick, and it's why the answer to "which mould remover actually works on sealant" is always a format answer, not a brand answer.
Where each format wins
| Surface | Winner | Why |
|---|---|---|
| Vertical silicone sealant | Gel | Needs hours of contact; only gel stays put |
| Washing machine door seal | Gel (brush type) | Folded rubber; gel painted into the fold stays there |
| Grout lines, vertical | Gel | Stains sit deep in porous grout |
| Painted walls and ceilings | Spray | Large area; surface growth only; gel would take all day |
| Tile faces | Spray | Non-porous, mould is superficial, minutes are enough |
| Window frames and reveals | Spray first | Mostly surface growth; gel for stained gaskets |
| Weekly prevention | Spray | Fresh spores die in minutes; cheap and fast |
The two-product system
Most homes don't need to choose. They need one of each, used for different jobs:
- One gel for restoration. Skylarlife for sealant runs, or GLOWPOINT if the main job is a washing machine seal. Applied properly, this is a once or twice a year job.
- One spray for maintenance. Astonish at £2 for the weekly wipe-down, or HG if you're also treating walls and ceilings.
And neither product fixes the reason the mould grew. If the room stays humid, it all comes back regardless of what you buy. That's the prevention guide, and it's the most important page on this site.
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