Mould Gel vs Bleach Spray for Black Caulk, Grout and Washer Seals
For black lines on shower caulk, grout and a front-load washer's door seal, a gel is the better tool because it stays on the stain: BLITZ Mold Stain Remover sits there 3 to 5 hours, while the Tilex label says to rinse after 10 minutes, and right away on rubber. It's the same active ingredient as a bleach spray, in a thick gel that doesn't run down vertical caulk. One 236 mL bottle does roughly 8 to 15 tub caulk lines, or a washer seal fold for 26 to 53 cents.
Our pick: BLITZ Mold Stain Remover
Use it on: black lines on caulk and grout, and the folds of a washer, fridge or dishwasher seal.
Recaulk instead: caulk that's peeling, cracked or black inside.
From a Québec company in Laval, septic-safe, with free shipping from $40 and a 30-day money-back guarantee. Prefer Amazon? BLITZ is on Amazon.ca too, without the 10% store credit.
Shop BLITZ Mold Stain Remover, $24.95
In this guide
Mould gel vs bleach spray vs DIY paste at a glance
Same bleach, a format that stays put. BLITZ's ingredients are sodium hypochlorite and sodium hydroxide; Health Canada's drug database lists Tilex Mold & Mildew at 2.4% sodium hypochlorite. What changes is where it ends up: a thick gel stays on vertical caulk for 3 to 5 hours, a spray runs off. The DIY paste here is baking soda and drugstore hydrogen peroxide; in our view it dries and crumbles off a vertical joint.
| BLITZ Mold Stain Remover | Tilex Mold & Mildew spray | |
|---|---|---|
| Active ingredient | Sodium hypochlorite (bleach), with sodium hydroxide | Sodium hypochlorite (bleach), 2.4% |
| Format | Thick gel, applied as a line | Trigger spray |
| Directions | Dry the surface, apply, leave 3 to 5 hours, wipe off and rinse | "Spray surface until thoroughly wet; let stand 10 minutes; then rinse" |
| Rubber seals | Washer gaskets, fridge and dishwasher seals are on its list | "Rinse immediately after use on rubber, plastic and vinyl" |
| Size and regular price | 236 mL, $24.95 | 946 mL, $5.79 at Canadian Tire |
| Shop BLITZ |
Checked October 20, 2026; prices move. Where to buy Tilex and what else is in each bottle: Tilex Mold & Mildew alternative.
Dwell time and runoff: 30 seconds, 10 minutes or 3 to 5 hours
On vertical caulk, a spray wets the line, then slides down it. A gel stays put. The labels set the clock: Tilex 10 minutes, the Clorox Clean-Up bleach spray 30 seconds, BLITZ 3 to 5 hours.
Our view: time wet on the stain is what lightens it. On a vertical joint a spray drains before its 10 minutes are up, and spraying again adds mist, not time.
Tip: Dry the surface first so the gel sticks (BLITZ's direction). Our suggestion: apply it at bedtime or on a day off, when nobody needs the tub or washer for 5 hours.
Washer door seals and rubber: what the labels say
The spray labels keep bleach off rubber or rinse it fast. Tilex says "Rinse immediately after use on rubber, plastic and vinyl"; Clorox Clean-Up says to avoid rubber. So a spray can't sit in the fold where the black lines are.
LG and Samsung both use chlorine bleach on the door gasket in their own care steps. BLITZ is a bleach gel made to stay there: washer gaskets, fridge and dishwasher seals are on its list. Run a line into the fold, leave it 3 to 5 hours, then wipe off, rinse and dry the fold. Full method: mould on a front-load washer gasket.
What the gel does on silicone caulk and grout
- It lightens surface stains. Old, deep stains may need a second round (BLITZ's direction).
- It stays on the line. The gel goes on as a bead right over the black, on vertical joints and the tub edge, with no mist on the tiles around it.
- Black inside or under the caulk means recaulk. BLITZ's FAQ says replacing the caulk is then the real fix; Sashco, a sealant maker, says mildew under caulk comes back through new caulk.
Surface or deep stain, the shower step by step, and when to recaulk: black shower caulking and grout.
What one treatment costs with BLITZ
At $24.95 for 236 mL on goblitzclean.com (October 20, 2026):
| Job | Gel used | Cost per treatment |
|---|---|---|
| Tub caulk line (about 3 m) | 15 to 30 mL | $1.59 to $3.17 |
| Kitchen sink caulk (about 1.5 m) | 7.5 to 15 mL | 79 cents to $1.59 |
| Washer seal fold (about 50 cm) | 2.5 to 5 mL | 26 to 53 cents |
The math: a thin gel line uses about 5 to 10 mL per metre, so one bottle does roughly 8 to 15 tub lines. Tub line: $24.95 × 15 / 236 = $1.59, × 30 / 236 = $3.17. Washer fold: $24.95 × 2.5 / 236 = 26 cents.
On goblitzclean.com the bottle also earns $2.50 in store credit, and shipping is free from $40.
Ventilation and never-mix rules, for either one
Careful: Health Canada warns that "Bleach will react with any cleaning product containing ammonia or an acid, including vinegar," such as glass and toilet bowl cleaners, and the gases can be deadly. Tilex adds rust removers.
- Use BLITZ on its own: its product page says never use it at the same time as another cleaner.
- Not with vinegar or the washer tablets either: tablet cycle first, drain, then the gel.
- Breathed fumes from a mix? Get to fresh air and call a poison centre (Québec: 1-800-463-5060).
- Air it out. Health Canada says to open windows or doors and run exhaust fans during and after use.
- Mist or a line. A spray puts droplets in the air; the gel goes on as a line. Tilex isn't recommended for people with heart conditions or chronic respiratory problems such as asthma.
- Eyes and hands. Health Canada recommends goggles and rubber gloves with bleach; BLITZ says the same for its gel.
- Too big for a bottle. Health Canada's mould infographic says to hire a professional above 1 m². Sink caulk and fridge seals: mould stains in the kitchen.
Real results with the gel
4.7 out of 5 (13 reviews) on goblitzclean.com. One customer praised the "thick no-drip formula" that stays on grout lines and caulking. For caulk, grout and rubber seals, we pick BLITZ.
- A Québec company in Laval, with service in French and English.
- Septic-safe, like every BLITZ product.
- Free shipping in Canada from $40 ($7.95 under). Most orders arrive in 2 to 3 business days.
- 10% back in store credit on goblitzclean.com, and a 30-day money-back guarantee. Also on Amazon.ca.
Get the gel that stays put, $24.95
Frequently asked questions
Is a mould gel better than a bleach spray?
For caulk, grout lines and rubber seals, yes: the gel stays on 3 to 5 hours, where a spray runs off and is rinsed after 10 minutes, right away on rubber.
What's the best mould stain remover for caulk?
For surface stains on vertical caulk, a thick gel that stays on for hours, such as BLITZ (3 to 5 hours). If the black is inside the caulk or it's peeling, recaulk.
Is BLITZ Mold Stain Remover bleach?
Yes. Its ingredients are sodium hypochlorite and sodium hydroxide: a thick chlorine bleach gel that clings where a spray runs off. Use it on its own, never with vinegar, ammonia, acids or the washer tablets.
Can I use Tilex on a front-load washer seal?
Its label says to rinse rubber immediately, so it can't sit in the fold. BLITZ lists washer gaskets among its uses and stays in the fold 3 to 5 hours.
How long do I leave mould gel on caulk?
BLITZ's direction is 3 to 5 hours on a dry surface, then wipe off and rinse. Old, deep stains may need a second round.
Sources, checked October 20, 2026: Tilex and Clorox Clean-Up labels (clorox.ca), Health Canada (bleach advisory, mould infographic, Drug Product Database), LG, Samsung, Sashco, the BLITZ product page; regular prices at Canadian Tire and goblitzclean.com. Brand names are trademarks of their owners; BLITZ is not affiliated with them.
STAYS ON THE STAIN
BLITZ Mold Stain Remover
A thick bleach gel that clings to vertical caulk, grout lines and washer seals instead of dripping off. Leave it 3 to 5 hours, wipe off and rinse. 236 mL, $24.95.
Free shipping across Canada on orders of $40 or more, 10% back in store credit on every order, and a 30-day money-back guarantee.
