Glass Block Windows

• Glass block is a building material developed in the 1900s for use in factories, according to the GlobalSpec website. Glass blocks were a desirable material for this purpose because they allowed natural light into the facilities while still providing thermal insulation. They were soon used for residential construction as well. Glass blocks are installed much like brickwork, with a silicone sealant to hold the blocks together and grout that provides the separations between the blocks. Small metal pieces are often used to hold the glass blocks in position, or a metal grid may provide the framework for the individual pieces.
  
  

Mortar

• The mortar around the glass blocks serves an important purpose. It provides a solid surface for holding the glass blocks in place and allows for structural flexibility. Ground settling beneath the window may cause enough movement in the structure to crack the mortar materials. The mortar will then need to be patched or replaced. Sometimes, the mortar fails because of improper mixing at the time of installation.
  
  

Locating Leaks

• Investigating leaks around glass block windows can be tricky. The leak may originate in an area above or around the glass block window and not from the window itself. Inspect the mortar around the glass blocks carefully to find cracking, holes or crumbling. If the mortar seems sound, then you can begin to suspect that the leak may be coming from another source. It may be a leak from a roof problem or a plumbing leak that has occurred somewhere above the glass window. Leaks from these other areas must be repaired or you will continue to have a leaking problem around your window.
  
  

Repairing Leaks

• Cracks and holes in the mortar should be repaired with mortar patching compound. If the glass block itself is cracked and leaking, it should be replaced by cutting into the mortar around the block with a diamond-cutting wheel, being careful not to damage other blocks. The damaged block is then removed, and the grout is chiseled out to give a clean surface. A new block is put into place with silicone. Fresh mortar is then set around the new block and allowed to dry.