DIY Brick Caps for Sills

Window sills are often trimmed out with a row of bricks called a cap.

Brick sill caps are installed beneath windows and doors. These caps cover bricks that have holes exposed. Additionally, they serve as trim pieces for windows and doors that are surrounded by brick walls. A homeowner can install brick sill caps with little or no experience, usually in two to four hours, depending on the size and scope of the project.

Things You'll Need

• Type N mortar
• Sand
• Shovel
• Wheelbarrow
• Mason's trowel
• Tape measure
• Bricks
• Right-angle grinder
• Masonry blade
• Brick hammer

Instructions

1. Measure the width of the window opening from brick to brick. Record the measurement onto a pad for future reference, especially if you are doing more than one window.

2. Divide the window width by 4 inches, which is the thickness of one brick standing on its side along with a 3/8-inch mud joint. For example, if your window opening is 40 inches, then you will use 10 bricks for the installation of the sill cap.

3. Cut the brick lengths to 6 inches. That will allow full coverage of the window sill and allow a 2-inch overhang. Cut the brick length down to 4 inches if you do not want an overhang. Cut the bricks with a right-angle grinder fitted with a 4-inch masonry blade.

4. Mix eight shovels of sand and half a bag of mortar in a wheelbarrow. Combine the mixture with a hoe. Chop the mixture with the hoe to remove any lumps. Add 3 gallons of water to the mixture to achieve a pancake batter consistency. Allow the mortar to set before proceeding.

5. Spread the mortar along the brick sill opening beneath the window or door with a mason's trowel. Pile the mortar up at about 4 inches thick, and rake your trowel point through the center of the mortar bed, creating a void in the center.

6. Spread mortar on the sides of one brick and place it on one end of the window sill. Press the brick into the mortar bed and at a slight downward angle -- but no more than 5 degrees. Repeat the process on the opposite side of the window sill. Allow the two outside bricks to set for 20 minutes.

7. Attach a nylon string to the two outside end-bricks using line blocks. Place the line blocks on the outer edges of the bricks, stretching the line across the window sill. Lay the remaining bricks in the window sill, aligning the edge of the brick with the nylon string.

8. Measure the opening after every two bricks to ensure that the mud joints are consistent. The measurements must always be divisible by four. Smooth the mud joints with a round thumb jointer after the mud has set for 30 minutes.

Tips & Warnings

• Mortar drying time will vary depending on the exterior temperature.

• Wear a dust mask and eye goggles when cutting bricks.

References

• "Masonry Skills"; R.T Kreh; 2002
• "Masonry & Concrete"; Benjamin W. Allen; 1997
• "Building with Masonry"; Dick Kreh; 1998