Installing Glass Block Windows in Basements

Consider purchasing a premade glass block window to install in your basement. This is a more expensive option but if you intend to place the window in a room you will use as a bedroom or family room, it should meet national ingress/egress standards, meaning it must be large enough for a body to pass through and it will open as a casement window. Check International Residential Code for the correct dimensions. (See Resources)

Prepare the concrete surface to install a traditional glass block window if you are not subject to ingress/egress restrictions. In this case, the window can be of any size and it will be stationary, due to the method of construction. The concrete should be smooth so chip off any rough protrusions and apply a thin layer of prepared mortar to fill any large holes or gaps. Use a trowel to smooth out the wet mortar.

Install glass blocks in direct contact with the surrounding walls. If, however, a wood frame is already in place, make sure to install metal flashing between the glass block and the wood frame to prevent moisture in the mortar from entering the wood, causing it to warp.

Begin in one bottom corner by slathering prepared mortar approximately ½-inch thick along the side and bottom where the first block will lay. Position the glass block and scoot it back and forth to settle it solidly in the mortar. Put a spacer on the top edge of the block, next to the open side where the next block will go.

Repeat the procedure for every block on the bottom level, alternately adding mortar, placing a block and then smoothing away the excess mortar. When the bottom row is in place, set a carpenter's level on the top of the blocks to make sure they are even. If there is any discrepancy now -- it will affect the level of the rest of the rows.

Continue to lay the glass blocks in rows, one at a time and leveling each one as soon as it is complete. If you have to take a break, do it only after an entire row is finished and leveled. Otherwise, the mortar will set up and manipulating the blocks will not be possible.

Keep a soft sponge in a bucket of warm water handy and wipe excess mortar off each row as you place the blocks. Be careful not to rub too hard or you risk scratching the glass. Change the water in your bucket regularly.

Remove the spacers by pulling and wiggling them a bit. They should come out easily. Fill large gaps with mortar and allow it to set. Apply a generous bead of silicone caulking around the inside and outside perimeter of your new glass block window.