Caulking Wood Windows
Wood windows are especially prone to damage from moisture. Water finds its way into the narrowest cracks and joints, where it can rot wood or peel paint. Every joint on a wood window should be caulked with elastomeric or silicone caulking. If you're going to paint or repaint the windows, look for paintable caulking. For windows that are staying natural or stained wood, choose caulking in the color that most closely matches the color of the wood, or use clear caulking. Caulk is usually available in a range of colors, including various shades of tan and brown, as well as gray, black, white and clear. The U.S. Department of Energy figures you'll need about one half of a tube of caulking for each window.
Vinyl or Aluminum Windows
Most vinyl and aluminum window units come caulked and sealed from the factory although over time, the caulk dries out and needs to be replaced. Choose silicone clear caulking. When applied, it's milky white but turns clear as it dries. Unpainted aluminum windows look good with gray or silver caulk because it matches the color of the metal.
Although caulk typically comes in disposable tubes that are fitted into a caulking gun for application, it's also available in squeezable tubes that require no gun and aerosol cans that apply expandable foam into larger gaps. Both of these types are messier to use. The squeeze tubes can be useful for small touch-up areas around your windows. Aerosol foam is best used for joints wider than one quarter of an inch, such as a wide space between the window trim and masonry siding. Since it expands as it dries, use a razor knife to trim it smooth.
Most caulking material is water-based and cannot be applied below 50 degrees. However, solvent-based caulking can be applied at any temperature although it will take a long time to dry in the cold. Some companies have water-based caulking that can be applied at any temperature above freezing and will dry quickly.