Mold or mildew: does the name matter
People use mold and mildew as if they are different problems. In practice, mildew usually means a flat, powdery or downy growth on a surface, often white or gray, and mold usually means a thicker, fuzzier or darker growth that can go deeper. Both are fungi. Both need moisture.
For cleaning purposes the useful question is not what to call it but how deep it goes, how big it is and what it is growing on.
Surface by surface
| Surface | Approach | Notes |
|---|---|---|
| Tile and glazed ceramic. | Detergent and water, scrub, rinse, dry. | Grout is porous, so scrub it well. |
| Painted drywall (small). | Damp wipe with detergent, dry fully. | Cut out if the paper is soft or stained. |
| Wood, sealed. | Detergent and water, dry fully. | Unsealed wood may need sanding. |
| Fabric and upholstery. | Wash or professionally clean. | Discard if musty after cleaning. |
| Carpet and pad. | Usually replaced if wet for days. | See the carpet guide. |
| Insulation and cardboard. | Throw away. | Porous materials hold growth. |
Safety for small jobs
Public Health Seattle and King County advises an N-95 mask, gloves and goggles for small cleanups, and says to dry surfaces quickly and thoroughly afterward. It defines a small area as less than about ten square feet, or a patch three feet by three feet.
Never mix bleach with ammonia or other cleaners. Open windows or run an exhaust fan, and keep children and pets out of the room. If you have health concerns, consult your physician.
A cleaning routine that works
Fix the moisture
A cleaned surface that stays damp grows mold again.
Protect yourself
Mask, gloves, goggles and a fan blowing outward.
Mist, do not dry brush
A light mist keeps spores from flying.
Scrub with detergent
Work from the edges inward and rinse with clean water.
Dry it completely
Fans and a dehumidifier for at least a day.
Bag the rags
Seal and discard rags and sponges.
Mold bigger than a small patch?
Call the 24/7 line. A person answers and helps you decide what to do.
When it is time to bring in a pro
- The growth covers more than about ten square feet.
- It came after a flood or sewage backup.
- It is behind walls, under flooring or in the HVAC system.
- The area returns after cleaning.
- Someone in the home has health concerns and needs a physician's guidance.
A mold remediation crew contains the area, filters the air, removes affected material and verifies that the area is dry. The scope is written down so you can follow it.
Why mold comes back
The EPA says the key to mold control is moisture control. Mold returns when humidity stays high, when a pipe or roof leaks, or when a building holds water in a hidden cavity. Every repeat of the problem is a message about the moisture source.
Check bathroom fans, dryer vents, window seals and plumbing. Keep indoor humidity low and let wet items dry within 24 to 48 hours.
Renters and shared buildings
If you rent, tell your landlord the same day and keep a written record. Tenants and landlords have different responsibilities depending on the cause, and a written report protects both sides. In a multifamily building, a leak in one unit can create mold in another.
Common household hot spots
- Window sills and frames where condensation collects in the cold months.
- Under sinks and behind toilets, where small leaks go unnoticed.
- Bathroom ceilings above showers with a weak or noisy fan.
- Closets on exterior walls where air does not move.
- Laundry rooms and dryer vents that exhaust into the room.
- Basements and crawl spaces that stay damp through the rainy season.
Prevention beats cleaning
Keep indoor humidity low, since mold and mildew thrive in damp air. A dehumidifier in the basement and a working bathroom fan do more than any spray.
Fix leaks as soon as you find them, clean small spots when they appear and let wet items dry within 24 to 48 hours. Open closet doors now and then so air can move, and keep furniture a few inches off exterior walls.
Check the places you rarely look. Behind the washing machine, inside cabinets under sinks and above the shower are where moisture builds up without notice.
Beyond the small patch
When growth is larger than a small patch, see mold remediation. If a leak caused it, water mitigation comes first.
Calls come in from Bothell, Kirkland and Woodinville.
The published ANSI/IICRC S520 standard is the industry reference for mold remediation. It is cited as a standard, not as a certification.
Common questions
Mildew usually describes flat, powdery growth on surfaces, while mold is often thicker and can penetrate. Both need moisture, and both are cleaned by removing the growth and the moisture.
Some people use vinegar on hard surfaces. Detergent and water with careful scrubbing and drying is the common state-agency approach. Do not mix cleaners.
Porous materials like drywall paper, insulation, ceiling tile and carpet pad that have been wet and moldy are usually replaced.
Multifamily buildings share walls and plumbing, so a leak in one unit can reach another. Report moisture problems early.