How to Install Preassembled Glass Block Windows

Measure the preassembled glass block window to be certain it will fit in the opening. Next, place some of the shims on the bottom, or windowsill, of the opening. These need to hold the window off the sill ½-inch. It’s best to set these 3 or 4-inches in from the corner to allow for mortar in the corners.

Apply some mortar on the sill without disturbing the shims. Remember that this window is very heavy, so it will pack the mortar. Be certain to place enough mortar on the sill so the weight of the window will pack it down to ½-inch. If you discover a few gaps, fill them without removing the window.

Place shims on either side of the window to even the gap on the sides. Be certain they match the gap on the windowsill as well.

Fill the areas on either side of the window with mortar. Remove the shims on the sides as you come to them, but leave the ones on the bottom (windowsill) of the window for last. Do not place mortar on the top of the window. Clean up excess mortar before it sets with a damp sponge and a clean, dry cloth. Wait 24 hours before caulking the top.

Fill the gap at the top of the window with foam caulking backer rod. Leave it back from the face of the window ½-inch. Apply the caulk in the gap so it finishes out to the face of the window. Clean excess immediately with lacquer thinner.