Q&A / 

Glass Blocks


DEAR TIM: I am intrigued with glass block. I would like to install this material in my basement windows, a bathroom window and as a room partition. Do you think an average homeowner can successfully tackle projects like this? How can I obtain the highest level of security for ground level windows? Can you offer any installation tips? Susan P., Franklin, PA

DEAR SUSAN: I share your fascination with these unique building blocks. Glass block products are very cool. They seem to be a timeless building material. I have installed glass block windows in 100 year old houses with little harm to the aesthetics. To date, I have not heard a complaint from my past customers concerning their usefulness, utility or durability.

I know that you will be able to handle the basement windows with little or no assistance. Depending upon the type of glass block window you choose, you may be able to do the bathroom window as well. The room partition is a job for a professional.

My guess is that you might actually use a combination of materials for your upcoming projects. Traditional glass block maybe the best choice for your basement window project. You can purchase solid glass block that are extemely difficult to shatter. These solid glass blocks will stop bullets fired from .357 magnum pistols!

Your bathroom window may be an excellent location for the clear or tinted lightweight acrylic block. You can actually get acrylic glass block windows that open and close. These will allow you to get plenty of air into these havens of mold and mildew. The acrylic blocks are available in clear, peach, rose and blue.

Your room partition may end up being constructed with thin glass block or the lightweight acrylic blocks to minimize the weight on your floor. The acrylic block can be ordered in widths and heights up to 9.5 feet in either direction. Traditional glass block will allow you to build large sized partitions as long as your mason installs the necessary hidden reinforcement steel.

Installing glass block panels in a basement window is very simple. The trick is to remove the old window and frame. Many cities and towns have fabrication shops that will make the glass block windows for you. You can specify the style of block and order it with little windows, dryer vents, combustion air inlets and other accessories built right into the block window. Your task is to simply install the entire unit at once.

Once you have got your new basement windows on site, check to make sure they will fit. A one half inch gap between the glass block window and frame is preferred. There is nothing worse than tearing out an existing window only to find out your new window will not work. To complete the installation you will need a bundle of wood shims, a small level, cement mortar, a small trowel and a sponge.

Place two one half inch shims about 3 inches in from the bottom corners on the bottom ledge of the opening. Apply your mortar mix to the bottom of the window ledge. Don't cover the shims with mortar. Tilt the window into position. Insert two shims between the top of the window and the opening. Tap them until they are slightly snug. Use the level to make sure the window is pumb. Check to make sure the gap around the window is uniform and that the window is not twisted in the opening.

Once you are satisfied with the position of the window, install the cement mortar around the sides of the window and the foundation. Once the mortar hardens in about 2 hours you should be able to gently remove the shims without disturbing the mortar or the window. Install mortar in the bottom holes. The top gap will be filled with foam expansion material and silicone caulk. Wipe the glass block with a damp sponge to remove mortar smears.


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