Why does black mold keep coming back in my shower caulk?
A straight answer first, then what you can do yourself and when to call a handyman.
Phones answered around the clock · free estimate
Black mold keeps coming back because it is usually growing underneath or inside the caulk, where surface cleaning can't reach, and because the joint stays damp long enough for it to regrow. The lasting fix is to cut the old caulk out completely, dry the joint, and lay a fresh bead of mould-resistant silicone.
The nuance is that caulk laid over old caulk, or over a joint that was not fully dry, simply traps the problem. If tiles are loose or the wall behind feels soft, the caulk isn't the real issue and the water source needs sorting out first.
Why it happens
Caulk is soft and slightly porous as it ages. Soap film, body oils and moisture settle into it, and mildew feeds on that. Once the mold has rooted into the bead or the gap behind it, bleaching or scrubbing the surface only lightens the stain. The roots stay, and the dark spots reappear.
Humidity does the rest. A bathroom without a strong exhaust fan stays damp long after the shower is off, and mildew grows in caulk quickly in those conditions. In colder climates, seasonal movement can also crack the joint where the tub meets the wall. That opens a gap where water gets in and sits.
Two repair mistakes make it worse: caulking over the old bead, so mold keeps growing beneath the new one, and using the shower before the new caulk has cured. Re-sealing around tiles that are already loose is another, because water may already be behind them.
What you can check yourself
Look at where the dark spots sit
Spots that look like they are inside the bead, or that reappear within weeks of cleaning, mean the caulk is past saving. Surface spots on newer caulk may clean off.
Check the exhaust fan
Run the fan during and after a shower and see whether the mirror and walls clear reasonably fast. A weak or noisy-but-ineffective fan keeps the room damp.
Look for cracked grout or gaps
Check the joints around the tub, the corners and the tile lines for hairline cracks or gaps. Those let water behind the surface.
Watch for loose tiles or soft spots
Look for tiles that seem to sit unevenly, grout that is crumbling, or a wall that looks stained or bulged near the tub. Don't pry at anything. Note it and mention it to the technician.
Dry the joints after showers
Wiping the caulk line and tub edge dry after a shower makes a noticeable difference. Keep the room ventilated, and never mix cleaning products.
When to call a pro
Call a pro when the mold returns quickly after cleaning, when the caulk is peeling or cracked in several places, or when you see loose tiles, failing grout or stained walls beside the tub. Those signs suggest water is getting behind the surface, and the technician needs to look at it before anything is sealed over.
One Call Handyman Repairs can line up a vetted, independent local handyman for caulking and grout repair. The estimate is free, the handyman looks at the job and gives the price before any work starts, and you approve it first. Call (888) 471-8212 or send a request through the website form. A fan that doesn't move air, or any electrical or plumbing problem behind the wall, is a job for a licensed trade rather than a handyman.
What the technician will do
- Cut out the old caulk completelyEvery bit of the old bead is removed, so no mold is left beneath new caulk.
- Clean and dry the jointThe joint is cleaned and left fully dry so the new silicone bonds properly.
- Lay a fresh bead of mould-resistant siliconeA clean, continuous bead goes around the tub, shower, sink or counter edges.
- Reach out cracked groutCracked grout is raked out and regrouted, and sealed if you want that.
- Explain the cure timeThe technician tells you how long to stay out of the shower so the caulk can cure.
Related questions
- Can I just caulk over the old caulk?
- It is better not to. Caulk over old caulk traps the mold beneath the new bead, and it tends to come back through. The old bead should be cut out and the joint dried first.
- How long before I can shower after re-caulking?
- Wait until the caulk has cured. Showering too soon can ruin the seal. Check the cure time on the product, and the technician will tell you how long to wait.
- Does grout need replacing as well?
- Only if it is cracked or crumbling. Cracked grout is raked out and regrouted, and sound grout can stay, with sealing if you want it.
- How much does it cost to redo shower caulk?
- It depends on how much caulk there is, how easy the area is to reach, and whether grout or tiles also need attention. The estimate is free, and the handyman confirms the price before work starts.
Get a handyman out
Free estimate. The price is agreed before the work starts.
Keep reading
One Call Handyman Repairs arranges the visit; the handyman does the work and gives you the price.