BLACK MOLD IN SHOWER
CAULK THAT COMES BACK

You scrub, you bleach, the black line along the tub disappears, and two weeks later it's back. That's because the mold isn't just on the caulk. It's growing underneath and inside it, where cleaners can't reach.

WHY CLEANING DOESN'T LAST

Silicone and acrylic caulk are slightly porous, and water gets behind any spot where the bead has lifted. Mold colonizes the gap between caulk and tile. Surface cleaning lightens the color but leaves the roots.

THE PROPER FIX

1. Cut out all old caulk with a utility knife and caulk remover tool.
2. Remove the residue completely. Silicone won't stick to old silicone.
3. Kill what's left with a bleach solution or mold remover in the joint.
4. Let it dry fully, ideally 24 to 48 hours with the fan running. This step gets skipped most often.
5. Fill the tub with water before caulking a tub joint, so the tub is at its lowest position.
6. Apply 100% silicone with mildewcide, tooled smooth.
7. Wait 24 hours before using the shower.

KEEP IT FROM RETURNING

• Run the exhaust fan during and 20 minutes after every shower.
• Squeegee walls and the tub ledge.
• Leave the curtain or door open after showering so the area dries.
• Fix low spots where water pools along the tub edge.

WHEN IT'S MORE THAN CAULK

If mold returns within weeks of a proper recaulk, or the tile around the joint is loose, water may be getting behind the tile. That's a waterproofing problem, not a caulk problem.

COST

Professional removal and recaulk of a tub or shower typically runs $150 to $325 in the DMV, and is often bundled with regrouting.

RELATED READING

Planning a project? See our Bathroom Remodel service page for scope, process and recent work.