Filling in a window opening might be undertaken for reasons of security, heat retention or remodeling. Whatever the reason, when you no longer want a window in its current location, one of the easiest ways to get rid of it is to fill it in with concrete blocks. This should be done only in walls that are built of stone, brick or blocks. The weight of all those blocks in a wooden wall might cause problems.
Things You'll Need
Remove the window sash and the window frame from the opening. If you're not planning to re-use the window frame, the easiest way to remove it is to cut through one of the side pieces with a reciprocating saw and bend and twist the frame out of the opening with a crowbar.
Attach mortar ties to the sides of the rough window openings at 8-inch vertical intervals so they will sit between the concrete blocks as you stack them up. The ties should be attached to the inside face of the opening with screws and bent so they are protruding horizontally into the opening.
Spread a 1-inch-thick bed of mortar along the bottom face of the opening using a mason's trowel. Spread mortar over the end face of a concrete block and seat the block in the opening so the holes in the block are sitting on the mortar bed and the end face of the block with the mortar on it is pressed against the side wall of the opening. Tap the block in with the handle of the mason's trowel so it's seated solidly and its top face is level.
Install another block next to the first by spreading mortar over one of its end faces and pressing this face against the end of the first block.
Cut a block to fit into the remainder of the opening when you reach the other side of the opening. You can do this with a masonry saw or by scoring a block with a cold chisel until it breaks in two. Install the cut block to complete the first course of concrete blocks.
Spread a layer of mortar over the top face of the first course of blocks. Seat the lowest masonry ties, which should be level with the mortar you just spread, in the mortar.
Install another course of concrete blocks in the same way that you did the first one.
Continue filling the window opening with courses of concrete blocks. Trim the height of the final row of blocks to fit the space between the row of blocks below it and the top of the window opening.
Wear gloves to avoid getting mortar on your hands. The lime in the mortar draws the moisture out of your hands and causes skin to become dry and uncomfortable.