What it involves: for surface mold on grout and caulk, cleaning and better ventilation. For mold behind tile, in the subfloor or inside the wall, containment, removal of the damaged drywall or backer board, cleaning the framing, and fixing the leak or the fan. Published Seattle-area ranges for a small bathroom job run about $800–$2,400.
Surface mold or a hidden leak?
Usually a cleaning job
- Spots on grout lines, caulk or the shower curtain
- Growth on painted ceiling near the shower that wipes off
- Comes back slowly over months
- Walls feel solid and dry
Usually something bigger
- Soft, bulging or stained drywall next to the tub or shower
- Loose tiles or cracked grout that keeps reappearing
- Musty smell that doesn't go away after cleaning
- Stains on the ceiling below the bathroom
- Warped vanity base or soft floor near the toilet
Why Bothell bathrooms grow mold
- Bath fans that don't vent outside. Many Bothell homes from the 1970s through the 1990s have fans that blow into the attic or into a loose duct. The bathroom stays humid, and the attic gets the moisture too. See attic mold remediation.
- Undersized or unused fans. A common guideline is about 1 CFM of fan capacity per square foot of floor in a standard bathroom, run during the shower and for a while after.
- Failed caulk and grout around tubs and shower pans, letting water into the wall.
- Leaking valves, drains and supply lines inside the wall or under the vanity.
- Condos and apartments. About a third of Bothell's housing is multifamily, and a leak from the unit above or next door is a common source, especially around Canyon Park and downtown.
How we remove bathroom mold
Find the water
Moisture readings around the tub, shower, toilet and vanity, thermal imaging of the walls, and a check of the fan and its duct.
Contain the bathroom
Plastic over the doorway with a zipper door and negative air, so the hallway and bedrooms stay clean.
Remove damaged materials
Moldy drywall, backer board, baseboard or flooring comes out, as far as the growth and moisture go.
Clean and dry the framing
Studs, plates and subfloor are cleaned and HEPA vacuumed, and dried to normal moisture levels.
Fix the cause
Plumbing repair, a properly ducted fan, or a new shower pan or surround, done by us or coordinated with your plumber or contractor.
Verify
Independent clearance testing before the wall is closed back up.
Condos, apartments and HOAs
When the source is in another unit or a shared wall, responsibility can fall on the owner upstairs, the HOA, or the landlord, depending on your declaration and lease. We document the source and the extent with photos and moisture readings so the right party pays. Renters: under RCW 59.18.060, Washington landlords must keep units reasonably weathertight and give tenants Department of Health information about mold. Report leaks in writing.
Keeping bathroom mold from coming back
- Run the fan during every shower and for 20 minutes or so after
- Squeegee or towel the shower walls
- Re-caulk tubs and showers when caulk cracks or pulls away
- Keep indoor humidity below about 60%, and ideally 30–50%, as the EPA recommends
- Fix drips under the sink as soon as you see them