How to Repair or Replace One Glass Block in a Glass Block Wall

Protect the floors on both sides of the wall by laying down drop cloths. Put short pieces of duct tape along the edges of the adjacent glass blocks on both sides of the wall. This will help protect the surrounding blocks during the repair and replacement process. Protect yourself with safety goggles and leather work gloves.

Saw into the mortar surrounding the glass block that needs replacing. Use a tile grout saw and make a 1/2-inch groove into the mortar on both sides of the block

Break and remove the glass on one side of the block. Tap a hole in the center of the block with a hammer. Continue to chip away at the glass with the hammer and carefully remove the pieces. Work from the center out toward the edges. Repeat this process on the other side of the block.

Chip away at the old mortar that was holding the glass block in place with a chisel and hammer. This includes the mortar around the rim and inside the hollows of the surrounding blocks. Take your time to avoid damaging the surrounding blocks. Vacuum the area thoroughly to remove all pieces of glass or mortar.

Follow the manufacturer's instructions and mix the glass block mortar with water in a bucket using a drill equipped with a mixer attachment. The consistency of the mixture should be spreadable and similar to thick pancake batter. If you're replacing one block, you can mix a small amount of mortar in a bowl.

Spray a fine mist of water around the inside of the hole. Put a 3/8-inch to 1/2-inch layer of mortar along the bottom of the hole. Rest a couple of pencils across the mortar. This keeps the mortar in place when you slide the new block into place.

Spread mortar along the sides and top of the new glass block with a margin trowel. Align the block with the hole and slide it along the pencils until it is flush with the surrounding blocks. Once it is in place, remove the pencils.

Pack the joints around the perimeter on both sides of the new block using a joint tool. Gently wipe away any excess mortar from the face of the block and surrounding blocks, front and back, with a damp sponge. Allow the mortar to set for 30 minutes.

Run the joint tool along the horizontal joints first and then the vertical joints to create a smooth, concave groove. Allow the block and mortar to set undisturbed for two hours. Gently buff off any excess haze with a dry, clean rag.