To avoid this check regularly for.
Repair cracked concrete window sill.
Stone windowsills add old world charm to many buildings.
Window sills are designed to divert water away from the house and as a result they get a battering from the weather over time wooden sills can rot and concrete window sills can develop cracks.
If it is broken under the window it would probably require taking the window out to repair.
Apply a 3 8 inch thick layer of concrete all over the sill with a trowel following any contours to mimic its original shape.
Resurface stained or cracked concrete window sills with new concrete.
Puddles of water collecting on the window sill.
Rub off flaking paint or loose concrete along the crack with the wire brush and make sure to clean out any moss that may be growing inside.
Cracked or worn paintwork.
Worn or loose joints.
If sills are sandstone the stone tends to deteriorate with age exposure to rain snow and freeze.
Use a paintbrush to apply concrete bonding agent to the entire window sill.
With concrete and slate sills the exposure to the variations in temperature can cause cracks and crumbling water penetration can also weaken the joints.
Here is a site that will help with replacing a concrete sill l that is not broken off all the way under the window.
Repairing a concrete window sill could appear to be a major job that s far beyond the skills of the average diyer but with the proper knowledge tools material and preparation you might find it s worth considering having a go yourself unless a complete rebuild is necessary.