How to Close in a Basement Window With Cement

Sal Marco

Homeowners may choose to close off a basement window to add wall space or achieve more privacy or security. Basement windows do not only act to allow potential unwanted individuals from entering, but may also trap occupants inside the home. Check local fire codes before attempting to close the window space. Many cities require an alternate escape route and officials consider windows as an emergency exit in case of a fire.

Use caution if planning to enclose a basement window, it may be deemed a hazard.
  1. Place masking tape over the window glass to keep the glass intact in case the glass breaks while removing the window. Masking tape will not prevent the glass from breaking, but it will prevent the glass from shattering over the work area.

  2. Pry off the surrounding window trim with a thin, flat pry bar or hammer and chisel. Insert a reciprocating saw blade into the space between the window and the masonry surface. Turn the saw on and cut the nails holding the window in place. Remove the window and discard or set aside for future use.

  3. Remove paint and loose concrete by brushing the rough window frame surface with a wire brush. Sweep away debris with a small hand-held broom.

  4. Inspect the rough window frame for cracks and holes. Press hydraulic cement into damaged areas with a putty knife.

  5. Mix type S masonry mortar mix with water in a wheelbarrow following the manufacturer's instructions. Type S masonry mortar mix resists weathering and is specialized for below-grade masonry projects.

  6. Apply an epoxy-based bonding agent on the interior surfaces of the rough window frame.

  7. Dip a trowel into the masonry mix and apply a 1/2-inch layer of the masonry mix along the base of the rough window frame and up the sides.

  8. Apply a 1/2-inch layer of the masonry mix to the bottom of a concrete block, cinder block, brick or stone. Determine what the existing foundation has and match the block, brick or stone to it or match it based on the size of the existing masonry.

  9. Set the first block in place along the inside bottom of the rough window frame firmly abutted to the side of the rough window frame. Apply a 1/2-inch coating of masonry mix to the second block and up the side of the block. Set the block in place next to and abutted tightly to the first block. Make cuts as necessary to the bricks or blocks with a masonry saw, brick set and hammer or wet saw.

  10. Apply a 1/2-inch layer of masonry mix along the top of the first course of block or brick. Apply a 1/2-inch layer of masonry mix to the bottom and up the sides of the next course of block you are setting. Set the brick or block in place tightly against the rough window framing and over the top of the first course. Continue to apply masonry mix, set blocks or bricks, course-by-course until block or brick covers the entire space.

  11. Allow the masonry mix to dry for 24 hours.

  12. Wet the block or brick with water.

  13. Mix type S masonry mix with water in a wheelbarrow. Dip a trowel into the masonry mix and spread it over the brick or block. Build up the layers until flush with the existing foundation.