Caulking Windows and Exterior Doors – Caulking along the outside of the frame of a window or door is important in sealing from water infiltration which is absolutely necessary in preventing water damage. A good rule of thumb is to apply a bead of caulk anywhere two dissimilar materials meet… brick and wood; wood and glass; wood and metal, etc.
Caulking Windows – Check for window drafts by carefully holding a stick of incense up to each frame and watch the smoke to see if there is a leak. (Be sure to remove all curtains and drapes first to avoid a fire.) Then use caulking or weatherstripping to seal the cracks. Another method is to work with another person on the outside, have that person blow a hair dryer around the outside of each window while you hold a lighted candle inside. If the candle flickers or goes out, you need to caulk or weather strip around the frame. Do not seal the exterior window weep holes shut, as these allow any water or moisture that does get into the window area to get out. Never use oil-based caulk to seal the seams of an insulating window. The oils in the caulk can degrade the bond around glass allowing moisture to seep into the house. The most obvious symptom of this problem is seeing your windows fog up during the summer.
Caulking Doors – All doors (entries, garage doors, and pet entries) need special attention. Problems are common where the doorframe meets the threshold. A thin bead of caulk can prevent water damage here. Also caulk the areas where trim meets the doorframe or siding. Don’t try to caulk the entire door jamb before going back and smoothing it out, do that as you go. Caulking starts to skin over quite quickly and then you can’t smooth it out properly.
Just another expert idea from Guy Calor, the Caulk King and CaulkWarmer