Latex Paints Sometimes Stay Tacky
Has this ever happened to you?
It's damp, it's rainy... and your exterior doors stick so badly that they are nearly impossible to open! You'll never see this happen with oil or "alkyd" paints. This tackiness problem is solely owned by latex paints! The problem is known as blocking, and can be caused by many factors such as applying an overly thick layer of paint, not allowing adequate drying between coats, reactions between the primer and the finish coat or the temperature at which the paint was applied... too hot or cold.
Want to get rid of the tackiness? Get rid of the latex!
First, don't use latex paint. Latex paints are a marvelous invention for many reasons but, in some applications and under some conditions, gloss and semi-gloss latex paints can develop a "tackiness" that seems to last forever. I painted a garage door with an exterior latex paint over 5 years ago and, in the warm weather, I still hear the sound of the tacky paint breaking contact as the door goes up!
The best way to avoid blocking is to avoid latex paints for 1) surfaces that contact each other and 2) surfaces you put things on, such as bookshelves. Use an oil-based alkyd paint instead, whether for inside or outside applications. Alkyd paints, which are the very top quality oil paints, dry hard and smooth and do not produce the tackiness you have been experiencing.
To paint over sticky latex paint with oil paint, what preparation is needed?
Yes, you can! There are mixed views among painters on preparation for a latex-to-oil changeover. In my experience, oil paint can be applied over latex without priming as long as the environmental conditions are not too demanding. Of course, a light sanding OR the use of a "deglosser" such as Wilbond is essential for a firm paint bond, and I don't want to discourage priming... it is a sure way to seal the latex and to assure the oil paint will stick for the long-term!
In the case of an exterior surface such as a door, I vote for light sanding followed by priming the doors prior to applying the oil. The primer must be an exterior grade and can be either oil or water-based. Again, there are some strong opinions on using either type of primer... just be sure it is an exterior grade. Under NO circumstances use Kilz, BIN, or any of the other interior primers.
Doors that are protected by an exterior storm door can have unique problems. Manufacturers of metal exterior doors generally frown on the use of storm doors, since the air space between the metal door and storm door can become hot enough under exposure to the sun to blister paint and distort the plastic moldings that some companies use to mount the window glass! This can also occur with wood doors, causing the paint to prematurely fade or appear weathered. In fact, this overheated situation can even cause wood doors to expand and contract severely enough to cause cracks in the door panels! And guess what makes the situation even worse? You guessed it… dark paint colors!
A final comment concerning blocking…
If you are not ready to repaint and would like to eliminate the tackiness, one method that I have used successfully is to apply auto or paste wax to the sticky area. The wax coating removed the tackiness, though it may have to be repeated occasionally if the tackiness reoccurs. Another "prophylactic" solution is to dust the area with talcum powder, which will stick to the sticky spots and lessen or eliminate the tackiness... for a while, anyway.
Nevertheless, the best and most permanent solution is to repaint with oil paint!