Glass block-from Pittsburgh Corning and other major manufacturersBuilders are using glass block to add natural light, enhance security, and to fashion room dividers, shower enclosures and a whole lot of interesting features in home designs.

If you've not specified glass block for any of your homes recently, you might be surprised at the wide array of blocks and products now available. Most people are familiar with the standard 4-by-8-by-8-inch clear block, but that's only one of many sizes and shapes available. There are square and rectangular blocks of various sizes, plus specially shaped corner blocks for ending a wall or turning a corner at a 45- or 90-degree angle.

When choosing glass block, keep in mind these five considerations:
•Visual privacy: ranges from low (see-through) to high (view totally obscured)
•Visible light transmission: indicates the percentage of light that passes through the block; typically ranges from about 30 to over 80 percent.
•Color: vast majority of glass block is clear, but color-tinted blocks are also available.
•Core: most blocks are hollow, but there are solid-core blocks, too.
•Finish: represents the type of finish on the block's surface, such as smooth, fluted, wavy pattern and grid pattern.

Glass Block Sizes and Colors
The standard size glass block is 4 inches thick by 8 by 8 inches square, which are its nominal dimensions. It actually measures 3-7/8 inches thick by 7-3/4 by 7-3/4 inches square. And although most projects use standard blocks, there many other sizes to choose from. For example, blocks range in thickness from 3 to 3-7/8 inches, and may be as narrow as 3-3/4 in. and as tall as 11-3/4 inches. The wide variety of sizes makes it possible to build projects to virtually any dimension; remember, unlike masonry brick or block, you can't cut glass block down to size.

Pittsburgh Corning Premiere Series glass block, Argus design

A vast majority of glass block used in residential and commercial construction projects is clear glass. However, you can also order color-tinted blocks in rose, blue or bronze. For the Sun Belt, there's a solar-reflective (low-E) glass block that has a metal oxide coating applied to the interior surface that reflects 75 percent of solar heat gain.

When specifying glass block for a project, take into consideration the visual privacy requirements. For a bar or basement window, you might want a totally clear glass block unit, but for a bathroom window, you'd need a design that obscures the view from the outside. The finish on the glass block determines the amount of visual privacy. A block with a smooth, clear finish is nearly transparent. A wavy-pattern or fluted block distorts images, but offers a modicum of privacy. A grid-pattern block totally obscures the view.

Pittsburgh Corning Premiere Series glass block, VUE design

Installation Options
Most glass block is laid in white glass-block mortar. The technique is similar to laying brick or concrete block. Depending on the height and overall size of the project, reinforcement is typically needed between courses to provide structural stability.

There are also two installation options that don't require mortar. One system uses wide plastic spacer strips placed horizontally between every course, and vertically between each block. The spacers and block are adhered together with clear silicone adhesive. Once the adhesive cures, the spaces between the blocks are filled with glass-block grout. The result is a glass block wall that resembles a traditional mortar-laid wall.

The other method is an all-silicone system. A series of plastic tracks and spacers are set between each block to maintain consistent spacing, then the joints between the blocks are filled with clear silicone adhesive.

Specialty Glass Block Products
Glass block manufacturers offer specialty products that enhance and simplify the use and installation of glass block units. One of the most popular of these products is a glass-block grid system for building glass-block windows and skylights. The anodized aluminum frames accept 3-1/8-inch-thick by 7-3/4-inch-square glass block units and come in wide range of standard sizes.

Hy-Lite decorative glass block window

Pittsburgh Corning, the world's largest glass-block manufacturer, offers LightWise, a prefabricated glass-block window that comes ready for installation in a variety of sizes ranging from about 16 by 16 inches to 32 by 80 inches. LightWise comes in a choice of vinyl-framed or aluminum-clad wood windows. Also see offerings from Hy-Lite Block Windows. There's also a line of prefab glass-block windows specifically designed for basements.

Glass-block shower systems are available for greatly simplifying the construction of shower enclosures. The pre-designed system includes everything you need to complete the project, including an acrylic shower base, shower doors, and the glass block, spacers, and other necessary materials.

Additional Resources
Mason Contractors Association
National Glass Association