What is Surfactant Leaching?
Surfactant leaching is a phenomenon is a relatively common exterior paint issue that is also known as streaking, weeping, surfactant staining and exudation. These stains are generally shiny and tan or brown in color and can occur with any exterior latex paint when certain environmental conditions occur. It can also happen on interior paints exposed to intermittent or continuous levels of high moisture or humidity (bathrooms, locker rooms, saunas, etc.).
What are Surfactants?
Surfactants are specialized soaps found in all latex paints. These additives provide paint with stability and keep it from getting too thick or separating. In addition, they help keep the pigments dispersed in the paint and help “wet” the substrate and allow the paint to more evenly flow and across the surface. Glycols are a commonly used surfactant found in most paint and the colorants used to give the paint its color. Dispersants are another surfactant that help ensure that when the colorants are added to paint, they are distributed evenly to provide the correct color and help prevent the color from changing when different application methods (brush, roll or spray) are used.
Surfactant Leaching Causes
During the curing process of latex paints, surfactants will slowly move to the surface of the paint and we washed away by rain and weather. The rate of this migration is dependent on the temperature and atmospheric conditions present as the paint is applied and died. If the paint is applied and dries in cool, damp, humid conditions or if exposed to dew or a light rain the surfactants will come to the surface very quickly and form the unsightly stains. This phenomenon can also occur if the air or surface temperature of the substrate is below 50º Fahrenheit during the application and drying process (See Florida Paints Technical Bulletin: FP01 – Cold Weather Painting). When these factors exist, the surfactants remain on the surface as the paint dries and causes streaking or staining. Dark, deep or vibrant colors are more prone to surfactant leaching because more colorant (a significant surfactant source) is required to achieve the desired color.
The surfactants will generally weather off naturally in a month or so. It can be washed relatively easily if the surfactants have not been baked by sunlight. If the leaching occurs in the first few days of application, the surfactants can usually be cleaned or rinsed off with a strong stream of water from a garden hose end sprayer nozzle. In mild cases, regular rainfall will wash the surfactants from the surface. Pressure washing can also be utilized to remove the surfactants, but care must be taken not to damage the freshly applied paint film. In severe cases, a soft bristle brush or sponge and a mild grease cutting dishwasher soap can help remove the stains.
To help prevent the onset of surfactant leaching, it is important to follow these guidelines:
1. Avoid painting when conditions are or are expected to be cool, damp, or humid.
2. Avoid painting if rain is forecast within 24 hours or painting within 24 hours of a rainfall as the air will be moisture-laden. Especially in cooler temperatures.
3. Avoid painting late in the day when mist, dew or other moisture may form on the substrate.
4. Do not paint if the air, material or substrate temperature is below 50º Fahrenheit or will be within four (4) hours of application.
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