Painting a Bathroom: Moisture and Mildew

A bathroom is the hardest room in the house for paint to live in. It goes from dry to saturated and back again every day, often several times, and the surfaces closest to the shower stay damp for hours afterwards. Near the coast the air is humid before anyone turns the water on. Paint that would last a decade in a bedroom can peel or turn spotted with mildew in a bathroom within a year or two.

Bathroom failures follow a pattern, though, and the pattern tells you what to do about them.

Why does bathroom paint peel?

Peeling in a bathroom is almost always moisture getting behind the film. Steam condenses on the coolest surfaces first: the ceiling above the shower, the wall on the outside of the house, the area around a window. If the paint was applied over a glossy old coat without sanding, over soap film, or over a wall that was still damp, it never gripped properly, and the moisture lifts it. Ceilings above showers peel first because warm, wet air rises and sits there.

The fix is not a thicker coat. The loose paint is scraped back to a sound edge, the edges are feathered so they do not show, and the surface is cleaned and dried before anything new goes on.

How do you tell mildew from dirt?

Mildew usually appears as black, gray or greenish speckling in corners, along the ceiling line, around the window and on the wall behind the toilet. A practical test is a drop of diluted household bleach on a cotton swab: mildew lightens within a minute or two, dirt does not.

Mildew matters because it is alive. Paint will not smother it. It grows back through a new coat, often in the same pattern it was in before, and the job looks worse than when it started.

The order of work in a bathroom

1. Kill the mildew. Affected areas are treated with a cleaning solution that kills mildew, given time to work, and rinsed. Scrubbing alone moves it around. Bleach is never mixed with ammonia or other cleaners.
2. Clean the whole room. Soap scum, hair spray and body oils leave an invisible film on bathroom walls. It is washed off so the primer can bond.
3. Scrape and repair. Peeling paint is taken back to a sound edge. Drywall damaged by water is assessed; soft, crumbling board around a tub or a leaking fixture is a repair, not a paint problem, and the leak has to be fixed first.
4. Let it dry. This step is skipped more than any other. Walls that look dry can still hold moisture, and paint applied over them traps it. The fan runs, the door stays open, and the room is not used for showers before painting.
5. Mask and protect. The tub, shower glass, vanity, mirror, toilet and floor are covered.
6. Prime where needed. Bare patches, repaired drywall, water stains and any glossy old enamel are primed. Water stains in particular need a stain-blocking primer, or they bleed through the topcoat.
7. Paint. Two coats of a paint made for humid rooms, applied at the thickness the label calls for.
8. Recaulk. Where paint meets the tub or shower surround, the joint is sealed with a paintable caulk where one is called for. Paint does not stick to silicone, so old silicone is removed rather than painted over.

Which paint suits a bathroom?

A good bathroom paint does two things: it forms a tight, washable film that sheds water, and it contains a mildewcide that resists growth on the paint surface. Both Dunn-Edwards and Sherwin-Williams make interior paints formulated for humid rooms, and Ebenezer chooses between them for the room and the finish you want.

Satin is the usual sheen for bathroom walls. It lets water bead and run instead of soaking in, and it can be wiped down without burnishing. Semi-gloss suits the door, the trim and the vanity if it is being painted. Flat wall paint does not belong in a bathroom; it holds moisture at the surface and marks every time it is wiped. There is more on choosing finishes in interior sheen room by room.

It is worth being plain about one thing: mildew-resistant paint resists growth on its own film. It does not stop moisture from getting into the wall, and it cannot make up for a bathroom that never dries out.

The fan does as much as the paint

The single biggest factor in how long bathroom paint lasts is ventilation. An exhaust fan that is noisy but barely moves air, or one that vents into the attic instead of outside, leaves the room wet. Running a working fan during the shower and for a good while afterwards, and leaving the door open, lets the paint dry out every day. If the fan is not doing its job, that is worth fixing at the same time as the paint, by the right trade.

The first days after painting

Paint feels dry long before it has cured. Steam on uncured paint can bring ingredients to the surface as sticky, tan or brown drips, most often on the ceiling. It is called surfactant leaching, and while it is mainly cosmetic, it is avoidable. Keep humidity low for the time the label asks, take shorter and cooler showers with the fan on for the first several days, and do not scrub the walls for a few weeks.

Coastal bathrooms

In homes near the water, like those in Imperial Beach or the beach neighborhoods of San Diego, the air itself carries moisture most mornings. Bathrooms on the outside wall of a coastal house stay cool and damp, mildew comes back sooner, and the drying step before painting takes longer. None of that makes the job impossible; it makes preparation and ventilation matter more.

Getting your bathroom right

Ebenezer manages every job personally, and that includes a single bathroom. He will look at the walls and ceiling, tell you whether what he sees is paint failure, mildew or water damage, and explain the steps involved before anything starts. If something is not right afterwards, he comes back and repairs it.

Ask for a free estimate for your bathroom, or read more about interior painting and how a job runs from start to finish.