It is best to never stain any exterior wood when inclement weather is forecasted, especially rain. Most deck stain brands will warn against application of their product within 12-24 hours of rain being forecasted. But as we all know sometimes the weather is not so predictable. So what do you do if it does rain shortly after staining?
You cannot do much until it stops raining once it starts. After the rain has passed and the deck has dried take a closer look. It really depends on how hard it rained and for how long. A light drizzle most likely won’t hurt anything but a good downpour can be a different story. The type and brand of stain can make a difference as well. Some stains can handle rain shortly after being applied better than others.