For my meat chickens tractor I used a lyme whitewash. I found instructions on the internet, bought a bag of hydrated lyme and went for it, (mix the lyme powder with water) even though my meat chicks won't be here till the end of April. It seems to be holding up really well, although it leaves a white dust on your hands when you touch it so I don't think I will do it for the coop, of course that will change if someone knows how to keep that from happening!
Did you use salt?
The problem you are having is called chalking and salt is one of the ingredients said to help with the chalking.
The basic Whitewash Paint is,
12 cups hydrated lime
4 cups salt
2 gallon water
Chris