Setting Glass Block Windows

Remove the existing window frame, if applicable, by cutting through it with a circular saw. Then pry the frame out of the opening using a pry bar.

Walk to the interior side of the window opening, and attach a 6-inch long wooden block to the upper portion of the windowsill outside the area where the window will reside. Secure the block using masonry or wood screws and a power drill. The block should hang down at least 1 to 2 inches, which prevents the window from falling out during installation.

Walk to the outside part of the window opening, and insert one wooden wedge on the bottom left side of the window opening and one wooden wedge on the bottom right side of the window opening. Set the pre-constructed glass block window into place with the help of another person if necessary.

Place a tape measure or ruler at the bottom of the window to ensure a 1/4-inch gap is under it. Then check for levelness by placing a carpenter’s level on top of the two wooden wedges. Walk to the interior side of the window opening, and insert a third wooden wedge under the bottom center of the glass block window.

Open a tub of pre-mixed mortar, and scoop up ¼ cup of it using a margin trowel or a pointing trowel. Press the mortar into the bottom gap under the window, skipping the areas with wedges. Add mortar to the top and sides of the window, and repeat the process on the exterior side of the window.

Wait until the mortar feels firm but not dry to your touch. Press a striking tool into the mortar, and pull it along the entire perimeter of the window to smooth the mortar.

Remove the wooden wedges and 6-inch long wooden block after the mortar dries completely, generally about two hours. Add mortar to fill gaps left when you removed the wood, and wait until that mortar dries.

Apply a 1/4-inch bead of silicone caulk around the inside and outside perimeter of the glass block window to seal the window opening.