Surfactants are an integral part of acrylic paint, helping to stabilize the pigments, among other things. The paint is designed so that surfactants either dry off during the curing process or are sealed into the paint. When there is excessive moisture or humidity, surfactants may rise or leach to the paint surface, causing it to become streaked or blotchy.
The primary causes of surfactant leaching include the following:
- Ambient moisture, or the amount of humidity in the air - Our technical data sheet suggests painting when it is below 50% humidity. Surfactant leaching is more likely to occur when there is high humidity. Often, humidity is highest overnight and lowest from around noon to early afternoon. If, for example, something was painted in the late afternoon, and then humidity set in overnight (or if it rained), that might be a factor.
- Dry Times - the paint might be dry to touch but the paint underneath may still be wet. If you apply a second coat before the first one is fully dry internally, moisture gets locked in, making surfactant leaching more likely. We typically recommend the dry time between coats to be 2-4 hours, which is typically adequate for interior painting, but because exterior conditions can be harder to control, dry times can vary much more significantly.
- Cure times - the final coat should adequately cure before being exposed to excess moisture. Typically it takes about 3-4 weeks for the paint to fully cure, however, in higher-moisture conditions it may take more time. Once the paint is 100% fully cured the surfactants are fully locked in, and should not leach.
- Substrate Moisture - Many surfaces can absorb moisture, especially if the ambient moisture is high, if it was washed recently, or if there was a lot of rain, necessitating a longer dry time than usual. The substrate needs to be completely dry from the inside out before painting, otherwise over time, moisture naturally will want to travel, pulling with it surfactants in the paint.
If you experience surfactant leaching, your best bet to remedy the issue is to do some or all of the following:
- Clean the surface as soon as possible: Use a strong stream of water such as from a hose, or give it a light scrubbing with a soft brush. Often, minor cases will wash off or resolve with normal weathering over time. This may very well solve the problem and you won’t need to do anything further. Sometimes, in high humidity areas, even after cleaning, the surfactant may continue to leach over time.
- If cleaning it didn't resolve the issue, you may need to repaint it during better conditions, so that this problem doesn't repeat:
- Make sure the humidity is low (ideally 50% or less),
- Make sure the surface being painted is completely dry,
- Give the surface adequate time to dry between coats,
- Make sure that rain or other forms of precipitation, as well as high humidity, is not in the immediate forecast.
- Possibly use a stain-blocking primer to help block out any existing moisture in the Hardie board (but again, allowing it to properly dry and applying the paint in correct conditions is the most important).
