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This document gives advice on how to find, test for, remove & prevent mold in bathrooms, including mold found on bath tiles, moldy tile grout, moldy caulk, and hidden bathroom mold. This is a chapter of "How to Look for Mold" which describes how to find mold and test for mold in buildings, including how and where to collect mold samples using adhesive tape - an easy, inexpensive, low-tech but very effective mold testing method.

This procedure helps identify the presence of or locate the probable sources of mold reservoirs in buildings, and helps decide which of these need more invasive, exhaustive inspection and testing. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Is Bathroom Mold a Health Risk or Indoor Air Quality Problem?

Allergenic bathroom mold: Our photo at left shows the most common place to find mold in a bathroom, on the tile grout or caulk. Usually this mold is a member of the Cladosporium sp. group, often C. sphaerospermum - among the most common molds found, and possibly allergenic. The total area of mold in this case is trivial and unlikely to be harmful to anyone. It is primarily a cosmetic issue. A close up of this bathroom mold on tile grout is shown at below (left). There is no need to perform a mold test to identify small areas of mold such as those shown here. Just remove the mold and correct the conditions that contribute to mold growth. Whenever cleaning mold, especially when opening a wall or ceiling cavity where you have found leak damage, remain alert for the discovery of a large moldy area (more than 30 sq.ft.). If a large area of mold is discovered, stop work, seal off the work area, and consult a professional. See MOLD TEST REASONS for details.

Our photos above show close ups of moldy bath tile grout. Mold may also be found in bathrooms on bath caulks (page to photo) and on the surface of ceramic tiles and even toilets and sinks where those surfaces have become coated with soap scum or organic dust and debris. These molds may appear to be "black mold" but on closer look they are usually brown members of the Cladosporium family.

Hidden Mold in Bathrooms - How to Evaluate the Risk of Harmful and Hidden Bathroom Mold

A bit of looking around may disclose larger and more problematic mold contamination in bathrooms. Here are some places to look:

• Look for hidden bathroom mold on the back side of wallpaper, especially above and around or near showers. Mold genera/species growing on paper surfaces such as on the back side of vinyl wallpaper or on drywall, painted or bare, are more likely to be harmful, possibly airborne species such as Aspergillus or Penicillium as well as the less easily airborne black bath mold Stachybotrys chartarum.
• Look for hidden bath mold behind floor trim and in wall cavities where the floor has been wet, and in the lower portion of wall cavities where floors have been wet.
• Hidden bathroom mold may be present in wall cavities around bath tub or shower controls that have leaked into the wall cavity. If your bathroom provides an access panel to the tub or shower controls from the other side of the wall, remove the panel and look for water stains there.
• Bathroom mold may be hidden in the ceiling, on the ceiling side of drywall around a leaky vent fan or light fixture opening, especially over or near a shower; Bathroom moisture related mold may also be present in other ceiling or attic spaces if the bath vent fan duct has not been properly sloped and routed outdoors.

• Bathroom vanity mold is often found growing on the back side or under-side of bath vanity cabinets - those un-coated surfaces pick up moisture and invite mold growth, particularly if the vanity is made of chipboard or pressboard. See our Photo Guide to Mold Under Vanity Cabinets below. Our photo (left) shows mold found under a built-in bathroom storage chest, visible only after the bottom drawer was removed to expose the wood subflooring.
• Insulation mold over bathrooms: on occasion, especially where a bathroom is not well ventilated or where the occupants do not use the vent fan system (maybe it's too noisy?) we find non-visible mold in ceiling or wall insulation, especially around ceiling penetrations for lights or fans. See FIBERGLASS INSULATION MOLD for details.
• Marble wall mold in baths? Mold may even be found on hidden drywall surfaces behind solid marble bath walls, as we show in our second case study of Photo Guide to Mold Behind Wall Marble below.
• Mold below bathroom floor tiles? Mold may be found growing on wood subfloors under bath floor tiles or sheet vinyl flooring if the bathroom floor has been wet or flooded. If a ceramic bath tile floor has become loose we suggest exploring for damaged subfloors - otherwise simply repairing the tiles may not be a durable fix. If the bathroom is not on a basement or slab, inspect the ceiling areas below the bathroom for leak stains. Stained areas of drywall ceiling below a leaky bathroom or bath fixture usually merit further investigation.

Photo Guide to Finding Mold Under or Behind Bathroom Vanity Cabinets

If there has been protracted leakage or spillage under built-in cabinets such as bath vanities, there may be a mold cleanup job under or behind these components.

We removed this bath vanity after receiving complaints of recurrent moldy odor in this bathroom. No amount of cleaning of other bath surfaces had reduced the mold smell. A slight slope in the bathroom floor had been sending tub spillage behind this bath vanity for a decade or more. Water spillage was inconsistent - it depended on who used the shower and how much water they splashed onto the floor.

What makes a lot of sense sense is to study the building carefully to decide on the building points at most risk of having been wet from leaks due to construction details or other site observations. That's where one would make a test cut. Like behind the vanity cabinet near the most moldy corner in our photo, above right.

We frequently add text and photos to this series of articles. See MOLD APPEARANCE - WHAT MOLD LOOKS LIKE and also to avoid spending on harmless non-mold debris see MOLD APPEARANCE - STUFF THAT IS NOT MOLD. Readers should also review Mold in Fiberglass Insulation in Buildings at our The Mold Information Center - What to Do About Mold in Buildings.

See Renovating to Avoid Mold Growth for specific tips that will mold-proof your bathroom, and see CONSTRUCTION DETAILS TO AVOID MOLD for a more broad list of details about mold-resistant construction in buildings.

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ACTION GUIDE - WHAT TO DO ABOUT INDOOR MOLD
AFTER THE MOLD CLEANUP
ATTIC MOLD
BATHROOM MOLD
  Is Bathroom Mold a Health Risk
  Hidden Mold in Bathrooms
  Bathroom Vanity Cabinet Mold
  Mold Behind Marble Walls
  Remove & Prevent Bathroom Mold
  Clean off mold on tile, grout, or caulk
  Renovating to Avoid Mold Growth
BASEMENT MOLD
BASICS YOU NEED to FIND, TEST, REMOVE MOLD
Basketball Mold Syndrome - BBMS
BLACK MOLD, HARMLESS COSMETIC
BOOKSTORE - ENVIRONMENTAL
BUYERS GUIDE - home inspections for mold
CARPET MOLD CONTAMINATION
CARPET TEST GUIDE
CARPET STAIN DIAGNOSIS
CARPET TEST GUIDE
CRAWLSPACE MOLD
DIRT FLOOR MOLD CONTAMINATION
DO IT YOURSELF MOLD CLEANUP

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More Information on Building Diagnostic Inspections and Repairs

Mold and Allergen Recognition and Identification - Not All "Black Mold" is Harmful; Some Suspect Stuff is Not Mold

• How to Find and Test For Mold in Buildings - Looking for Mold - A 'how to' photo and text primer on finding and testing for mold in buildings
• Recognizing Mold: What mold looks like mold identification photos to help identify mold - choosing what to sample in buildings
• Recognizing Allergens: What various indoor allergens look like - identification photos to help identify pollen, dust mites, animal dander, toxic or allergenic mold - Common Mold and other Allergens, Irritants, Remedies & Advice
• Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
• Mold Action Guide: an easy step by step outline of what to do about mold
• How to find mold without hiring anyone, for do-it-yourself'ers
• Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
• Mold Test Kits - How to Collect and Send Your Own Mold Sample to our mold testing lab
• How to find a mold inspector or test consultant: Directory of IAQ,Sick Building, Mold Allergen Testing, Building Investigation Service Providers
• Meruliporia: the house eating fungus or "poria"
• Mold Investigation Tips for Home Inspectors how to find mold, where to look, what is likely to be important. Advice to building inspectors intending to inspect or test for toxic or problematic mold indoors, mold inspection methods, and mold test methods which are valid or invalid
• Mold Risk Levels in Buildings Based on Visual Inspection - simple visual clues help decide on action
• Mold in Fiberglass Insulation© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation - DJF
• Frequently Asked Questions About Mold -- check this FAQ list & IAQ Site Map to see if you can find a quick answer to your mold concern
• When to hire a professional to inspect for toxic mold or other allergens
• Contact Us to arrange mold/IAQ building on site inspection and testing.

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The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

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