A problem that occurs weeks or months after the completion of a painting job is seldom a paint-related issue. More frequently, they are due to the environment in which the paint was applied, or the environment in which the surface has been kept since. Humidity is the main concern in both cases.
This is one of the misconceptions regarding interior painting. Once the paint is dry, people think that what happened during the paint job doesn’t matter anymore. It’s not like that. Moisture impacts paint in all stages, from its application to the wall until years after it has been applied. Having some understanding of the effects of humidity on paint and finishes often helps to understand the reasons why some rooms require repainting far sooner than others and why two identical paint jobs in the same house can act in totally different ways.
What Happens When Paint Goes On in High Humidity
New paint must release moisture while curing. That process occurs at a rate influenced primarily by the conditions in the surrounding. If the humidity level is high, the air surrounding the wet paint already contains a lot of moisture, making it more difficult for the paint to release some of its moisture.
The effects of this are more severe than a longer dry period:
- Blistering. When moisture is trapped under or in the paint, paint bubbles will form as the paint dries. They may show up when the paint is still wet, or hours after the paint has passed through various stages of curing.
- Poor adhesion. When paint is applied to a surface that contains condensation or ambient moisture, and the paint has not been absorbed, the bond will not be as robust as when paint is applied to a dry surface. The bond between the coating and the substrate is weak in the beginning.
- Sagging and runs. In high humidity conditions, the surface tension process that helps to hold fresh paint in place is slowed down. That paint that is supposed to stay on the wall begins to slide, particularly on vertical surfaces.
- Extended curing times. A coat that should be ready for a second application in a few hours might still be tacky eight hours later. If the next coat is applied too early, without the proper cure of the first coat, adhesion issues will occur between layers.
Bathrooms and Kitchens Are the Most Vulnerable Rooms
These two rooms produce more moisture in a home than any other room and that moisture directly and continuously affects the durability of the paint.
In bathrooms, steam from each hot shower goes into a comparatively small, confined area. If the ventilation isn’t sufficient, that moisture is present in the air and deposited on the walls and ceilings throughout the week, week after week, year after year. Typical indoor paints were not designed for that much exposure to moisture. Even paints marketed as bathroom paints need proper ventilation to perform the way they’re designed to.
It’s the ceiling that suffers the most. Bathroom ceiling paint is the first to fail because hot air and steam ascend and settle on the ceiling surface before they disperse. The combination of poor ventilation and poor paint choice for bathroom ceilings is the most common cause of peeling, bubbling, or mildew formation on the ceiling.
Kitchens are another form of the same issue. During cooking, steam and moisture containing grease is released which condenses on the walls close to the stove and on the surface above the cooktop. This is one of the reasons kitchen walls have to be prepared a little more extensively before repainting than other walls, and why kitchen paint tends to peel or discolor faster.
What Moisture Does to Paint Over Time
The application stage isn’t the only time humidity causes problems. The effects of continuous moisture exposure accumulate over the course of months and years and gradually affect paint finishes.
Mildew and mould growth: When ventilation is inadequate, high-humidity surfaces can become breeding grounds for mildew. It appears as spots, typically in corners, around the edges of ceilings or behind furniture where the air will not circulate as freely. The spots are not always mould growing on the paint itself. They are frequently nourished by organic material contained in the paint film, such as dust, soap residue or biological material.
Efflorescence. Mineral salts in the soil are drawn to the surface and form a white, powdery deposit under and/or through the paint on the wall in rooms where moisture is moving from the outside. Any treatment of the efflorescence or painting over it is not a solution, as it doesn’t resolve the moisture problem. Salts continue to migrate, and the paint continues to flake off.
Paint softening. Over time, paint films will soften, harden, and soften again from repeated cycles of high humidity followed by drying. This cycling will slowly affect the integrity of that film, leaving it more prone to scuffing, staining, and then failing to adhere.
Colour and sheen change. The behavior of pigments and binders in paint over time is influenced by high humidity. Colors may change and sheen levels may vary from the initial application, and may become uneven due to moisture stress on the paint film over time.
The Role of Sheen Level in Humid Spaces
Paint sheen is not just aesthetic but also a practical choice and is most important in rooms that have moisture issues.
Flat and matte finishes are porous. They absorb moisture more easily than higher sheen finishes and are not well suited to bathrooms, kitchens and laundry rooms. They are also hard to clean without harming the paint surface, which is a problem in rooms with walls that require regular wiping down.
Satin, semi-gloss and gloss finishes feature a denser, less porous film that is more resistant to moisture and will withstand cleaning. The drawback is that the more sheen the paint has, the more likely it is to reveal surface flaws, so it is even more critical to prepare the surface for painting when using semi-gloss or gloss paint. That’s not an issue if the surface is properly prepared. When texture variations or patchwork are not addressed on a surface, a higher sheen will amplify everything.
The reason that satin or semi-gloss is the recommended finish for bathrooms and kitchens is not that it is waterproof, but that it is much easier to maintain than other available finishes, and can be cleaned frequently without degradation.
Ventilation Is the Variable That Changes Everything
Even high-quality paint systems don’t work well in a room where moisture can’t escape. How a bathroom is ventilated can make the difference between a manageable humidity level and spending most of its time saturated.
If the exhaust fan is functioning and is used during and after showers, it will make a significant difference in the longevity of paint in a bathroom. The fan must be appropriate for the size of the room, properly vented out instead of into an attic or wall cavity and be used regularly, not just occasionally. It is not just applied during showers, but after showers for 15 minutes to allow moisture in the air to evaporate before coming into contact with surfaces.
In the South Okanagan, where Evolved Contracting operates in Summerland, Penticton, Peachland, and West Kelowna, the interior humidity will change throughout the seasons. During the winter months, the air is drier and can cause paint to crack on surfaces that were painted in warmer months with higher humidity. That means older houses without air conditioning may have more humidity during the summer than people realize, especially in an area known for its dry heat. Both extremes matter when selecting paint products and timing applications.
Getting the Paint Selection and Prep Right for Your Space
The right paint for a kitchen or bathroom isn’t just the one that says it’s suitable for those rooms on the label. It’s the one that’s selected based on the specific conditions of that space, applied over properly prepared surfaces, and put on in conditions where it can cure correctly.
Kary and the team at Evolved Contracting assess each surface and room before selecting products or starting work. That includes looking at ventilation, existing moisture damage, surface condition, and the history of what’s been applied before. Over 20 years of painting across the Okanagan builds a clear picture of what holds up in these specific conditions and what doesn’t.
Call Evolved Contracting at (604) 966-4449 or email evolvedcontracting@proton.me to talk through your project before any commitments are made.