Painting in the rain
It rains a lot in the Pacific Northwest so people often ask how long does paint need to dry before it rains, or what we do about rain. You shouldn’t paint when it rains. Sometimes we need to get a house painted and it’s raining, so what are the options? And why exactly is water an issue?
Let’s start with the solutions.
Sherwin Williams Resilience
Miller AcriMax
Special Paint for rain
Most of the major paint brands have come up with specialty products for painting in less than ideal conditions. Sherwin Williams Resilience and Miller Acrimax are both formulated to cure quickly. These can develop moisture resistance in 2 hours or less. My local SW store told me that they tested the 2-hour claim on Resilience by spraying water on the house with a garden hose and the paint held up.
If the weather is otherwise good but could change quickly, I would recommend using a specialty paint. Early spring-time and late fall is when we use a lot of Resilience paint.
So why did the paint companies come up with these new products? Why can’t they just make one paint that works all the time?
If the paint dries at a normal speed when it is cold, then it will dry too fast in the heat. For example AcriMax dries so quickly it is advised to only spray it, and not brush or roll.
Watching paint dry
- How long does it take for exterior paint to dry?
Usually 4 hours for normal paint to properly cure in good conditions. It can dry to the touch within an hour, especially if it is hot.
- How long does paint need to dry before rain?
Special paints can be rained on after 2 hours. No paints can be applied over moisture.
- How do oil based paints react to rain?
Technically moisture won’t absorb into oily paints, but at minimum the surface finish will be impacted. Premature failure is likely even with an oil based paint if it is rained on before it cures, or if the wood underneath wasn’t dry.
DIY chemistry
There are also additives that can be added to paint to make it dry faster. The most popular is rubbing alcohol or isopropyl alcohol (IPA). When a small amount is added it evaporates quickly and takes water with it. This is not recommended as it typically voids the paint manufacturer warranty and could interfere with the paint curing chemical reaction known as cross-linking. This is basically when the paint melts together and becomes a single skin or coat (also called the paint hide) on your house. If you’ve ever wondered why the paint is water-based but doesn’t dissolve again in water, it’s because of this chemical reaction. Kind of like how like wet concrete cures and then is waterproof.
Some painters report good results with this technique, but your mileage may vary.
Problems
The obvious problem when it rains is that it is wet. You don’t want to seal moisture into your house (especially if you are painting wood!) because all it takes is one hot day to have all the water evaporate and leave through the paint. This causes peeling, blistering, and general paint failure.
The rain can also land on top of the paint and wash it away, and mix with the paint. This ruins the final finish and dissolves into the paint, thinning it down, and taking longer to dry. This means the paint job will probably be uneven and have runs and drips, and no one wants that.
Humidity can cause these same problems even if no visible water touches the paint. High humidity means that moisture will be sealed into the painted substrate and the paint will take longer to cure.
Book early to avoid problems
By the time summer rolls around and the weather is right for painting, it is usually too late to book with most painters. The lead time is usually a few months, so if it is currently raining you should book now.