Mold in the Basement, Bathroom or Attic: What to Do in St. Louis

Why does mold grow in a basement?

Mold grows where there is moisture. EPA says none of the many types of mold will grow without water. Homeowners often find it in basements. Fix the water source, or the mold comes back.

EPA says to dry wet or damp materials within 24 to 48 hours of a leak or spill. In most cases, mold will not grow if you do. Past that window, it can. The City of St. Louis gives the same advice: clean within 24 to 48 hours.

Common moisture sources EPA names for a house:

• A leak or spill that was never dried.
• Water collecting around the foundation, when the ground does not slope away from the building.
• Clogged or broken roof gutters.
• High indoor humidity. EPA suggests keeping it below 60 percent, ideally between 30 and 50 percent.
• Condensation on cold surfaces such as cold water pipes.

This page does not claim a cause for your basement in particular. Finding that cause is the first job, and it often takes a site visit. Our guide on mold after water damage covers flood and leak cleanup in more detail.

How do I know if the mold is more than 10 square feet?

Measure the patch you can see. About 10 square feet is roughly a 3 ft. by 3 ft. square. EPA says a smaller area is often a do-it-yourself job. A bigger area, or a lot of water damage, is where EPA points you to professional guidance.

Visible mold may not be all of it. EPA says hidden mold can sit on the back of drywall, wallpaper or paneling, under carpet and pads, and inside walls around leaking pipes. A musty smell with nothing in sight is a clue. If you suspect hidden mold, consider an experienced professional.

For the size rule in depth, read mold over 10 square feet. For a visit that finds the spread and the source, see mold inspection.

What do I do in the first 48 hours?

Stop the water, then dry everything. EPA and the City both say to dry or clean within 24 to 48 hours. Open doors and windows and use fans, as the City advises. Remove wet items you cannot dry. Then fix the leak or moisture source.

Use this order:

1. Stop the source. Fix the leak or stop the standing water.
2. Dry the area. The City says to open doors and windows and use fans.
3. Sort the contents. Throw away porous items that stayed wet over 48 hours and cannot be cleaned and dried.
4. Clean hard surfaces. EPA says to scrub mold off hard surfaces with detergent and water and dry them completely. The City says to use a stiff brush on rough surfaces such as concrete.
5. Fix the cause before you repair or paint.

Do not paint or caulk moldy surfaces. EPA says to clean up the mold and dry the surface first. If the water came from sewage, stop and call a professional.

Which basement materials can be cleaned and which must go?

Hard, non-porous surfaces can usually be cleaned. Porous, absorbent materials often cannot. EPA says ceiling tiles and carpet may have to be thrown away if they become moldy, because mold fills their empty spaces. The City adds drywall, insulation, paper and wood to its list of items to consider removing.

The City lists carpeting, carpet padding, drywall, floor and ceiling tiles, insulation material, wood and paper among the items it may be best to remove after more than 48 hours of wetness. These are guidance, not a rule for your house. A professional can judge each item.

AES handles the heavier version of this work. See home mold removal for what AES says about mold in houses, and mold remediation for the service. Terms: mold remediation, mold spores and containment.

What about mold in the bathroom?

Bathroom mold is usually a ventilation and cleaning problem. EPA says that if it keeps reappearing, more ventilation and more frequent cleaning will usually prevent it, or at least keep it to a minimum. Run the fan or open a window when you shower.

EPA also says to cover cold water pipes with insulation to stop condensation, and to keep humidity in check. If mold covers a ceiling, wall or floor beyond a small patch, or if a leak sits behind the wall, treat it like the basement case above. Check the table for the 10 square foot line.

What about mold in the attic?

Attic mold points to moisture from above or from trapped air. EPA names roof materials above ceiling tiles as a place for hidden mold, due to roof leaks or insufficient insulation. A stained ceiling below, or a musty smell upstairs, are common clues.

EPA’s other moisture advice applies too: clean and repair roof gutters, and dry wet materials within 24 to 48 hours. Beyond that, we will not guess about attic ventilation or roofing. Those depend on your roof, and a person needs to see it.

Before you disturb old attic insulation, read our guide on asbestos in older St. Louis homes. It covers vermiculite attic insulation.

How do I stop mold from coming back?

Fix the water problem. EPA says that if you clean up mold but do not fix the water problem, the mold will most likely return. Cleanup is not finished until the moisture problem is completely fixed. Control humidity and watch for new damp spots.

Habits that help, in EPA’s words:

• Keep indoor humidity below 60 percent, ideally 30 to 50 percent.
• Run the bathroom fan or open a window when showering.
• Clean and repair gutters, and keep the ground sloping away from the foundation.
• Insulate cold water pipes.
• Dry any new leak within 24 to 48 hours.

AES offers moisture barriers as one of its services. Learn the term: moisture barrier. A barrier is a tool, not a cure for a leak. Find the source first.

When should I call a professional?

Call when the growth is large, hidden, or tied to heavy water damage, sewage or your HVAC system. Also call if someone in the home has health concerns. EPA says to consult a health professional before cleaning if you have health concerns. A pro finds the source and contains the work.

Check how a company will contain the area and whether it will test the result. EPA says surface sampling may be useful to judge whether an area was adequately cleaned, and that the people who sample should have experience. See the difference between terms in mold remediation vs. mold removal, and read about black mold.

For cost factors, see the mold remediation cost and timeline guide. AES quotes each job and does not publish a price here.

Advanced Environmental Services, Inc. (AES) serves residential, commercial, industrial, governmental and healthcare customers from 3100 Gravois Ave in St. Louis. Its work includes mold remediation. The service area is St. Louis and projects within 300 miles.

Next step

Learn about our mold remediation service, or call (314) 865-2662 to talk about your basement, bathroom or attic. You can also send the details through our quote form. Tell us the room, the size of the area and how it got wet.