Moisture on the surface is not a problem for "3in1" during application. If the surface is (too) wet there is no film (you see small "rivers"), but some moisture is taken from the surface by the watersoluble part of our solvents and goes to the surface of the paint and evapurates together (if it gets a chance to dry during the drying process. If a surface with moisture is painted in the morning and it dries during the day, that´s fine. But you cannot coat a cold-water-pipe with constandly cold water running through, it will hardly ever dry.) But if there is any chemical like salt or detergent on the surface and is overcoated, then we will see a bubble and corrosion under the paint.