How to get dark buildup off bathtub caulk
Persistent dark buildup along bathtub caulk often resists heavy scrubbing with standard foaming cleaners because it is deeply embedded or trapped beneath the seal. Trying to clean or replace the caulk without addressing the underlying accumulation leaves the film behind, leading many to mistakenly believe the discoloration is permanent or structural.
What the numbers show
Counted from the threads quoted below. How we count
- The most recent one is from October 2026.
- This comes up 14.9× more often in r/CleaningTips than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Asking apartment maintenance to take a lookDid this help you?
- 2Scrubbing with a rag and scrubbing bubbles foamerDid this help you?
- 3Attempting to scrape the edges with a caulk tube and a scraperDid this help you?
- 4Leaving shims in place and caulking around or over them.Did this help you?
- 5Soaking the buildup with CLR using a paper towel for 24 hours and chipping it away with a plastic scraperDid this help you?
- 6Scraping out the entire corner substance and replacing it with caulkDid this help you?
- 7scraping off all the old caulk, cleaning the surface with alcohol, ensuring it is completely dry, and letting 100% tub and shower silicone cure for at least 12 hoursDid this help you?
- 8Using a plastic putty knife to scrape the buildup offDid this help you?
- 9Scraping away old caulk, cleaning with alcohol, and applying new silicone.Did this help you?
- 10Calling the landlord to replace the affected sink part.Did this help you?
- 11Scrubbing until nothing comes offDid this help you?
- 12Filling up the tub so it is under load when caulkingDid this help you?
- 13Removing old grout, spraying bleach, letting it sit, cleaning dry, and applying silicone caulkDid this help you?
- 14Using bleachDid this help you?
- 15Using vinegar and bicarbonate soda left sitting in the bathDid this help you?
- 16Scrubbing with elbow greaseDid this help you?
- 17Using ceramic glass top cleanerDid this help you?
- 18Using a steel spongeDid this help you?
- 19Applying vinegar, alcohol, and everyday bathroom cleaning suppliesDid this help you?
- 20Using Barkeeper’s friendDid this help you?
- 21Using citric acid mixed with dish soapDid this help you?
- 22Soaking an old cloth in warm white vinegar or CLR and letting it sit wrapped around the encrusted partDid this help you?
- 23scrubbing with over ten different products including dish soap, tile cleaner, and bleachDid this help you?
- 24contacting the landlord to handle the recaulkingDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Hello everyone, new bathtub, less than 4 months, and we noticed some holes and dark spots on the original caulking.”source ↗
“I scraped everything, cleaned with alcohol and applied new silicone. It didn't last couple weeks when the dark spots returned and now looks like shit again.”source ↗
“This caulking keeps peeling after a few months. Any suggestions?”source ↗
“it looks like there are still areas of black along the crease where the tile meets the tub. Should I continue with more concrobium, or is it safe to assume that the mold/mildew is dead and that the little bits of black is more colour than active mold at this point? Should I move ahead and apply caulking?”source ↗
“I just started using a plastic putty knife to scrape this yellow stuff off my shower walls, but I’m worried I also scraped the paint off.”source ↗
“Just moved into a new apartment and the bathroom sink has this stuff stuck to it. Have managed to get a little bit off using a steel sponge. I’ve tried vinegar, alcohol and any other everyday bathroom cleaning supplies I had laying around. What do I do?”source ↗
“I just bought a house and the bottom of the shower stall looks like this. All four corners and the edges are coated in this stuff that is hard like concrete.”source ↗
“The second picture is after letting laying a paper towel on it with CLR soaked in for almost 24 hours, and then chipping it off with a plastic scraper. But it would take weeks to do that allll around the edges.”source ↗
“what’s the best way and products to remove a lot of accumulated soap scum, without damaging grout and silicone joints, please?”source ↗
“There's this rubber ring around the bathroom sink that constantly seeps this orange gunk (I assume some type of mold) and leaves leaking splotches on the counter when it gets wet.”source ↗
“Is there any product I can use to help control this better, or is this a "live with it unless you want to call the landlord to replace something" situation?”source ↗
“I have no idea what is causing these black marks on my bath.”source ↗
“I have tried bleach/ vinegar and bicarbonate soda left sitting in the bath but nothing has helped. It has just smeared slightly.”source ↗
“No amount of elbow grease will get it off the bath”source ↗
“It looks like when nail polish marks the bath to me. If anyones figured out how to get that off id appreciate knowing 😅”source ↗
“I had this issue with an acrylic tub.”source ↗
“I’ve tried absolutely everything. Started with the less harsh stuff (not at the same time) dishes, tile cleaner, bleach. Over ten products. I hate the way it looks. Any idea? We do rent. This is happening over the caulking but there are some parts that’s not.”source ↗
“That mold is underneath the silicone caulking, which means no surface cleaner will reach it and the caulk needs to be scraped out and replaced”source ↗
“If bleach didn't kill it, you're probably going to need to remove the caulking and replace.”source ↗
“It’s also on the tub too and that won’t come off. Is this something we do on our own or is this something that we have our landlord do”source ↗
“I can’t respond with a photo but it’s on the side where the glass door slides. There is some caulking that the landlord did shittily but it’s an inch or two below on the actual tub.”source ↗
“That mold is trapped underneath the silicone layer, so scrubbing the top won't work no matter what product you throw at it”source ↗
“Every few months, this darker kind of tan film starts to collect around the edges of my bath-tub.”source ↗
“I have scrubbed this as hard as I possibly can with a rag and some scrubbing bubbles foamer and it won't come up so that's why my belief was it was something else.”source ↗
“Attempting to change the caulk on a toliet in a house we moved into a few months ago and ran into this, do I have to remove the toliet to get it all out?”source ↗
“The tile is unfortunately grouted down to the tub. What are the recommended steps here for removing the cracked and moldy grout and re-silicone?”source ↗
Where this came up
People with this problem also raised
- 42How to get bright, oily bath bomb stains out of a tub
- 17How to fix white spots on a shower floor finish
- 7How to remove loose grout wedged between tiles
- 5How to remove baked-on old gasket maker and RTV
- 11How to get rid of mold around shower pipes permanently
- 4Pulling off the substrate when removing window caulk