How to Install Glass Blocks Without Mortar

Set the glass block window frame inside the window opening. Check that it is level and plumb, or straight up and down, using a carpenter’s level. Add wood shims as necessary to level the window frame. Pull it back out of the window opening without disturbing the shims. Nail the shims into the window framing to hold them in position.

Run a bead of silicone caulking in a wavy pattern along the back side of the flange that goes around the window frame, using a caulk gun. Slide the window frame back into position in the opening. Secure it to the house with nails or screws driven through the pre-drilled holes in the frame.

Slide one glass block into one of the glass boots that come with the glass block window frame. You might have to turn the block to get it to fit into the boot because not all glass blocks are completely square.

Push the boot, along with the glass block, into one of the openings in the window frame from the exterior.

Repeat Steps 3 and 4 until all the openings in the window grid have blocks in them. Check the appearance of the window inside the house to ensure the boots are all in their proper position. Push the boots farther in if they aren’t set properly.

Run a bead of silicone caulking along each of the grids to seal the glass blocks in place. Depending on your glass block grid, there may be a channel to fill with caulking. Dampen your finger and smooth the surface of the caulking with it. Wipe off any excess caulking from the glass blocks.