7 Signs of Hidden Mold After a Leak (and When to Test)

• 12 Jun 2026
• By Evan Mercer
• 6 min read

The most common signs of hidden mold after a leak are a persistent musty odor, stains that return after painting, bubbling or soft drywall, warped baseboards, allergy-like symptoms that improve when you leave the house, and visible growth on the back of cabinets or around HVAC equipment. Mold needs moisture, and in Central Texas homes that moisture usually comes from a plumbing leak, an AC condensate problem or water damage that was never fully dried.

1. A musty smell that will not go away

Mold releases volatile compounds with an earthy, stale odor. If a room smells musty even after cleaning and airing out — especially a closet, bathroom or laundry area — there is often moisture and growth behind a surface.

2. Stains that come back

A water stain painted over once and back a few months later tells you moisture is still reaching the surface. The drywall paper and framing behind it are prime spots for growth.

3. Bubbling paint or soft drywall

Paint that blisters, drywall that feels spongy or crumbles at the bottom edge, and nail pops in a small area all point to water inside the wall.

4. Warped baseboards and flooring

Baseboards pulling away from the wall, swollen door jambs and laminate or wood flooring that cups near a bathroom or laundry room are classic signs of a slow leak.

5. Growth under sinks and behind appliances

Look at the back and underside of sink cabinets, behind the washer and around the refrigerator’s ice-maker line. Small drips there go unnoticed for months — as in this laundry drain leak we remediated in Pflugerville.

6. Problems around the HVAC system

In Austin, attic and closet air handlers produce gallons of condensate a day in summer. A clogged drain line or rusted pan can wet ceilings and insulation below, and the dark, warm space is ideal for mold.

7. Symptoms that ease when you are away

Stuffy nose, itchy eyes or coughing that improves when you leave home can be related to indoor mold. Talk to your doctor about health concerns; we deal with the building.

Mold is never the root problem — moisture is. Remove the growth without fixing the water and it comes right back.
— Evan Mercer, Founder & IICRC Master Water Restorer

When should you test for mold?

If mold is visible, you do not need a test to know it should be removed. Testing is useful when you smell mold but cannot find it, after remediation to confirm the area is clean, or during real estate transactions. In Texas, mold assessment for areas of 25 contiguous square feet or more is performed by a licensed mold assessor, who writes the remediation protocol, and the remediation is done by a separate licensed remediation contractor.

What professional remediation involves

1. Find and fix the moisture source — often with a moisture mapping inspection.
2. Contain the area with plastic sheeting and negative air pressure so spores do not spread.
3. Remove damaged porous materials such as drywall and insulation, then HEPA-vacuum and clean framing.
4. Dry and verify before any rebuild starts.

Learn more about our mold remediation service, or call us to schedule an inspection if any of these signs sound familiar.