How To Replace Glass Block Window Panes

If you have a broken glass block window, you don't have to replace the whole window. Glass block windows are made from single blocks of glass joined by mortar or plastic spacers. It is possible to replace single glass blocks. You don't need advanced skills to replace glass blocks. Here are some tips the replace glass block window panes.

Prepare to Work

For this project, you need:

  • work gloves
  • safety glasses
  • tape measure
  • cloths
  • vacuum
  • paper bag
  • bucket
  • pliers
  • duct tape
  • utility knife (optional)
  • putty knife (optional)
  • rubber mallet
  • hammer, pre-mix mortar or plastic spacers and silicone sealant
  • trowel
  • striking tool (a narrow spatula)
  • replacement glass blocks

Wear thick pants and long sleeves. Pick up as many pieces of glass as possible with gloved hands, and vacuum to pic up glass shards you may have missed. Pull out any remaining shards in the pane with the pliers, and discard the pieces in a paper bag.

If the glass block is just cracked, place masking tape on one sides of the block to secure it. Gently tap both sides of the glass with the mallet so the glass falls and sticks on the duct tape

Remove the glass and discard it. Measure the glass block openings that need replacing, and use the measurements as a guide to buy replacement glass.

Install Traditional Glass Block Replacement 

Chip the old mortar off with the hammer and chisel, taking care not to damage good glass. Mix mortar in a bucket to the consistency that matches the thickness of the other joints. This is usually the thickness of bread dough.

Apply mortar with the trowel on the bottom of the opening. Clean excess mortar with a damp cloth before it dries. Don't use abrasive to clean the window.

Set the glass block in place. Allow the mortar to dry for about two hours, then check for evenness. Use the striking tool to even the mortar, and clean excess mortar with the cloth. Apply mortar in the same manner to the sides and top, and on the other side of the window.

Install Glass Block Replacement Without Mortar

Remove old spacers, and scrape old sealant with the utility knife. Place the new glass in the opening. Insert the new spacers around the glass; tapping them with a mallet to push them in place, if needed. Apply the sealant around the edges with a putty knife, and let it dry.

Your glass block window should look as good as new. If you don't trust your skill, or the window is on a higher level or seriously damaged, contact a window replacement service, such as Distinctive Siding & Window.