Grout, caulk, tile and window sills: a cleaning job, not a contractor job
These are hard, non porous surfaces in spots that get wet every day. The EPA says to scrub hard surfaces with detergent and water and dry completely. The fix that lasts is less moisture.
What is probably happening
- Bathroom: steam with no working exhaust fan, or a fan nobody runs long enough.
- Window sills: condensation on cold glass in winter, dripping onto the sill.
- Black spots in caulk mean the mold is inside the caulk. You replace the bead, you do not scrub it.
Do this in the next five minutes
- Scrub with detergent and water. Dry the surface. Wear gloves and open a window.
- If the caulk is stained through, cut it out and re caulk with a mildew resistant kitchen and bath product.
- Run the bathroom fan during and 20 minutes after every shower. If there is no fan, crack the window.
- Wipe window condensation each morning until the weather changes.
- Keep indoor humidity below 60 percent, ideally 30 to 50. A $15 hygrometer tells you where you are.
Do not
- Do not call a remediator for grout. Under about 10 square feet on a hard surface is inside the EPA's do it yourself range.
- Do not fog or ozone the bathroom. The moisture will bring it back next month.
- Do not mix bleach with any other cleaner. CDC: never mix bleach with ammonia or any other cleanser.
Who to call
Usually nobody. An electrician or HVAC contractor if the fan is the problem
The mold is the symptom. If the bathroom has no exhaust fan, or the fan is dead, that is the trade to call, not a mold company.
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What it should cost
$500 to $1,000
Bathroom mold remediation if you hire it out. Most of these are a $10 bottle of cleaner and a tube of caulk
Source: Angi, mold remediation cost, July 2026. View source
National published range, not a quote for your job. The full cost table for this trade is on the mold page.
Ask this contractor, on the phone, before anyone comes out
Tap each one as you ask it.
- Is the bathroom fan actually venting outside, or into the attic?
- If you are quoting remediation, what is the moisture source and is fixing it included?
- Will you replace the caulk or just clean it?
End the call if
- A remediation quote for a shower with no mention of the exhaust fan.
- An air test sold for mold you can see on grout.
- A 'whole house treatment' pitched for a bathroom.