How to Add Windows to a Cinderblock Wall

Measure the edges of the window you plan to install in the cinderblock wall. Cut lengths of 2-by-4 pieces of lumber to construct a frame around the window, then drive wood screws through the joints at the edges of the frame.

Mark where you plan to cut the window opening, using the window’s frame as a stencil. Hold the window frame against the wall and place a level along the top, bottom and side of the frame to ensure it sits level. Trace around the outside of the frame using a piece of chalk, then set the frame aside.

Put on protective goggles and a face mask before continuing. Cut a 1/4 inch deep line along the chalk lines you drew using a concrete saw. Adjust the saw’s blade to make a 1-inch deep cut, and cut along the same lines again.

Strike the bricks within the cutout using a sledge hammer. Knock off any rough edges in the opening, using the claw side of a masonry hammer.

Slide the window frame you constructed in the opening you created. Drive concrete nails through the fame and into the surrounding blocks, anchoring the frame in place. Apply an even bead of silicone caulk around the edges of the window frame, filing in any gap between it and the cinderblocks.

Insert the window into the frame you anchored in the opening. Drive shims around the perimeter of the window to center and level the window in the frame, and then drive galvanized nails through the fins on the edge of the window and into the frame.

Mix mortar with water, following the ratio on the mortar’s bag. Spread the mortar on the exterior of the opening, filling in any gaps between the blocks and the window frame using a putty knife. Cut the vinyl trim that came with the window, so it fits around the window opening and over the frame, and then nail the trim to the cinderblocks. Apply silicone caulk evenly around the edges of the vinyl trim.