Air Leaking Around the Grout of Glass Block Windows

Block Window Systems

• Many glass blocks come with complete installation systems that include mortar or grout. Directions found along with the systems provide detailed instructions on putting the glass blocks together into window form. In general though, a block window is installed by creating a frame in the wall, just as you would for a standard window, followed by applying grout or mortar along the bottom of the frame, laying the glass blocks into the grout and mortar, and working your way up to the top of the frame.

Spot Grouting

• If you can see holes around the glass blocks in a window, and this is where the air is leaking around the grout, you sometimes can fill in these leaky holes by spot grouting. To spot grout, place just enough grout on the tip of a putty knife, and apply the grout directly to the sections of the glass block window where the holes are visible and the air passes through. If the hole was the issue, spot grouting should stop the air flow.

Replacing Mortar or Grout

• If you see no visible holes in the grout and the air seems to be leaking from the entire grout job, the window may have been improperly grouted. To repair a bad grout job, you must remove the grout that already lies in the spaces between the blocks and replace the grout. Scrape out grout from the vertical lines between the blocks only with a chisel and hammer, and apply the grout again, making sure to get the grout all the way to the bottom of each space.

Caulk

• Another option to fill in the holes that cause leaking air in the grout of glass block windows is to fill in the spaces with caulk, instead of grout. Use a silicone-based caulk, which provides the necessary water resistance and durability for glass block windows, and apply the caulk to the holes found in the grout. If the caulk won’t ruin the appearance of the window, you may want to apply a bead of caulk over the top of all of the grouted spaces of the window to create an airtight seal.