JND Enterprises

Newly installed window frames have a channel built into them that is used for gripping the caulk and securing it in place.

 

If this channel is not caulked, then the caulking only adheres to the side of the window, thus making the caulk prone to shear. 

Often on newly installed windows the brick opening is a little too large and the window has a pretty big joint that needs to be caulk, if you caulk the gripping channel it makes for a wide joint that is unsightly. To get around this problem you can only caulk to the side of the window thus not having caulked the gripping channel, this makes caulk failure more likely, to solve this problem you need to apply a deeper bed of caulk. So it is essential to get the openings as close as possible during construction, a tighter opening makes for a neater and better caulk joint.