Window sills are designed to shed water. Bricks are not. Brick window sills are notorious for spalling (see "Spalling"). Concrete sills, however, are designed to shed water. They have a smooth surface and a drip edge underneath, used to keep water away from the wall below. Replacing deteriorating brick sills with a new Indiana Limestone sill is commonly reccommended, unless preservation of archetectural or historical integrity is desired.