The Proper Way to Build a Brick Window Sill

By Brian Scudder

Builders use brick to construct window sills in residential and commercial buildings. Although appealing, brick window sills create moisture problems due to the number of horizontal joints in the sill. Brick sills constructed with the correct slope, pointing away from the building, provide ample drainage. Preparation of the wall before the brick is installed remedies the moisture problems. Installing flashing and weep holes -- holes that prevent water from entering the building -- before installing the brick sill is crucial for keeping out moisture. The "rowlock" brick pattern is common for window sill applications.

Things You'll Need

  • Folding rule
  • Pencil
  • Bricks
  • Brick hammer
  • Brick chisel
  • Weep hole wicks
  • Mortar
  • Mason's trowel
  • Level
  • Brick jointer
  • Stiff bristle brush

Step 1

Measure the distance from the window to the outside of the brick wall. The underneath side of the brick sill must extend past the face of the brick wall a minimum of 1 inch.

Step 2

Lay the brick on a flat surface with the holes facing up. Mark a 15-degree angle on the end of each sill brick. Mark the end closest to the window.

Step 3

Place the brick chisel on the line you marked. Strike the chisel with the hammer to cut an angle on the brick end. This allows the brick to fit under the window trim.

Step 4

Install weep hole wicks by placing them horizontally on the flashing, spaced every 16 inches. Allow the wicks to extend slightly beyond the front of the flashing.

Step 5

Apply mortar to top of the flashing with the trowel.

Step 6

Install the bricks on the wall below the window sill. Place them on a 15-degree angle, sloping away from the window. The brick spacing should match the width of the mortar joint on the wall.

Step 7

Use the level to check for a straight and level surface.

Step 8

Smooth the mortar joints with the brick jointer. Sweep off excess mortar with the broom. Allow the mortar to dry.

Step 9

Clean the brick with water and a stiff brush after the mortar has dried.