Can You See Through Glass Block Windows?

Detail Shot Of Glass Block
Rolfo Brenner/EyeEm/Getty Images

Glass block has long been used in homes as a way to bring natural light and a feeling of openness to rooms yet maintain privacy.  

Homeowners' love for this material ebbs and flows throughout the decades.  If you're going for a 1940s post-Deco film noir look, you can do no better than creating a curved glass block window on the front of your home.  It was used again during the 1980s, making those homes look severely dated during the next decade.

 No doubt it will rise again in popularity.

Where and Why?

Glass block is used in place of conventional clear glass exterior windows at the front of the house or on bathroom windows.  It is also used as an interior non-load-bearing wall, along foyers or in bathrooms.

Privacy is the top reason this material is installed.  While lounging in the bathtub, you can get a reasonable amount of natural light filtering through an exterior glass block window, but it is impossible for anyone to look inside.  Even a snooper who puts his/her eyes right up to the glass will only see amorphous, vague images inside.

You can also use it for interior screens, such as in bathrooms where you might want to shield the toilet area from the rest of the bathroom.  A conventional interior wall, built with studs and drywall, would only cast the toilet area in darkness.

Why Is It "Dated"?

Glass block, as noted earlier, seems to have its hot and cold periods in the area of design.

 And when it's cold, it's ice-cold.

That Pasadena-house-Film-Noir look you're trying for often doesn't translate to houses that aren't in Pasadena (California) that weren't built in the 1940s.  It just looks like you're overreaching.  

Or more likely, it's a South Beach Miami (Florida) look.  Since much of South Beach was built up in the Forties and included glass block, and was then again revived in the 1980s and 1990s, using glass block in your home might date your home to 1984 more than 1944.

Self-Supporting But Not Load-Bearing

Glass block looks as solid and substantial as brick, but it does not have load-bearing capabilities. It cannot bear loads other than its load.

Homeowners often lose sight of this because glass block is installed much like a brick, with mortar. But you need to think of glass block just as you would a window: a fully self-supporting opening with fragile glass inside.

Not only that but for exterior walls, you will find that glass block is so heavy that it requires a sturdy base with a properly built sill and cripple studs running vertically below it.

Kits Make Construction Easier

Instead of building glass block windows and screens from scratch, pre-fabricated kits make the job easier.  Installing glass block in your bathroom or even exterior can be a frustrating project because the material is so heavy and requires a precise opening (glass block cannot be cut).

But prefabricated glass block window units operate just like any other kind of replacement window. They have the glass blocks already installed in the unit, and the units have nailing flanges on the perimeter. These prefabricated glass block window units are then installed just like any other type of window.

Use Special Mortar

Do not use regular brick mortar. You will need to use a premixed glass block mortar.

Why can't you just use plain old mortar? Because brick mortar has high water content, and this water gets "pulled away" by capillary action by the porous brick. Glass is not porous and so will not pull the water away. Glass block mortar is drier than brick mortar.