How to Install Glass Block Windows in 10 Steps

Proper measurement is the first step in ensuring the successful installation of a glass block window panel. Measure from the inside jambs, then subtract 1/2 inch from the window’s length and height. This allows you to construct a curb using mortar underneath the window panel. Once you have the proper measurement, purchase your pre-assembled glass block window panel at your local home improvement store or place a custom order from your favorite brand.

Wear eye protection and work gloves for this next step to prevent injury from broken glass or other materials. Use a wrecking bar to carefully pry out the old window jamb (the sides creating the frame). Cut the wood sill using a handsaw or circular saw while being cautious not to cut through the concrete or supporting wall. 

Afterward, remove the sill, side jambs, and head jamb. You may need a utility knife to remove the old caulk and paint. Confused about all the different parts of a window? It might be time to put down the saw and call a pro.

You should fasten a wooden block temporarily beneath the sill plate using screws. It will prevent the glass block window from slipping during installation. You will want to ensure that the block extends downward sufficiently to prevent the glass block window panel from tipping inward. If your home lacks a sill plate, simply attach the block to a joist instead.

Grab a helper for this next step. One person will be outside the window opening. The other will be inside.

Place the bottom of the window on two wood wedges from the exterior side. The bottom of the window will slide inward a bit. Your helper inside and the block will help stabilize the window during the positioning process.

Now that the window is in position, it’s time to ensure that it’s level and centered. To accomplish this, use your level and adjust the wedges. You can use wood shims for further adjustments and to secure the window. Ensure your helper is on the other side of the window in case of slippage.

Afterward, measure the distance from the center of the window to each of the four corners to ensure it is centered, or square. You may need to adjust the wedges and shims to secure the window. Then, check your work using your level once again.

First, gather the necessary materials, including mortar mix, a bucket, water, trowels, a drill, a scoop, and a grout mixing paddle. You must also wear your work gloves because mortar can harm the skin.

Next, measure the mortar mix using the scoop and add it to the bucket based on the manufacturer's instructions. Afterward, add water gradually, pouring it into the bucket while continuously stirring it with a trowel.

It is essential to mix the mortar thoroughly until it becomes one consistent mixture, ensuring no dry or lumpy areas are left behind, just like you would with pancake batter. Grab your drill and pop on the grout-mixing paddle to get the job done.

When the mixing is complete, let the mortar rest to activate the bonding agents for better workability. It should take up to 15 minutes. Making small batches of mortar is a good idea to avoid waste throughout the project.

From the exterior side of the window, fill the gaps under and alongside the glass block window panel with mortar, ensuring a thorough packing. Begin by packing the bottom and smoothing the curb where the window sits, avoiding contact with the wedges and shims. Allow the curb to harden to the touch before moving on to the sides. This will enable you to brush off any mortar crumbs that may have fallen onto the curb. 

Next, fill in the sides, avoiding any additional wedges and shims.

Then, use a margin trowel and a pointing trowel to fill in any additional gaps alongside the panel. Once the mortar has stiffened slightly, use one of your trowels to smooth things.

Once the curb for the glass block window panel sets, remove the wedges and shims. Remember that the mortar must be properly set and hardened before performing this step. For timing, it is a good idea to refer to the mortar manufacturer's instructions. As a rule of thumb, the mortar will require at least two hours to set or up to five hours in cooler temperatures.

Carefully fill the gaps that the wedges and shims have created with mortar. Once the mortar is stiff, you can smooth it out with a trowel. Afterward, you must wait several hours for the mortar to completely dry and set.

Now, ensure a watertight seal from the window's exterior and interior sides with weather-resistant caulk. You must apply it to the gaps or seams between the glass block window panel and the wall. Don't skip this step because it is crucial for keeping unwanted moisture out.

Grab your trusty tube of weather-resistant silicone caulk and place it into your caulking gun. Carefully apply the caulk along the entire perimeter. Take your time to ensure a thorough and even application, leaving no room for water infiltration or pesky drafts.

Now you can stand back and enjoy the natural light.