Largely overlooked since their popularity in the 1980s, glass blocks are making a comeback as a way to enjoy light with privacy, improved security, and an upscale ambiance. Reinvented in fresh, modern ways, they’re showing up not just as exterior windows, but also in partition walls, showers, and other interior features.
These blocks, also known as glass bricks, aren’t as easy to work with as glass panes, so incorporating them into your home takes careful planning.
Glass Blocks Through the Years
Mouth-blown glass blocks were used in the 1800s to let light into underground spaces such as storage cellars and below ship decks, but they lacked the durability for serious architectural use. In 1907, Friedrich Keppler, founder of the Deutsche Luxfer Prismen-Gesellschaft, patented a mechanical process for producing reinforced concrete frames embedded with solid glass blocks, which offered greater strength.
In 1935, Corning GlassWorks further improved on the idea with a process for joining two sections of glass to create a hollow block known as the Corning-Steuben block. These blocks are lighter, insulate better, and diffuse more light, so the same basic process is used today.
The glass in modern blocks is typically 2 to 3 inches thick, much thicker than the 3/32-inch glass used for standard windows. Blocks are available in a variety of sizes, shapes, colors, and patterns to let you create the look and level of privacy you want.
To build your glass block feature, you can either buy individual blocks and mortar them together like bricks or use a pre-made glass block panel designed to be installed as a single piece.
Pros and Cons
Aesthetics – The luster and timeless elegance of glass brings a touch of glamour to a home, improving the ambiance and adding curb appeal. Mixing blocks of various sizes, colors, and patterns lets you turn even the dullest wall into a showpiece. Because glass blocks were so widely used in the 1980s, they do have something of a retro vibe, but for many, that’s part of their appeal.
More energy efficiency lighting – Thanks to their thickness and hollow centers, glass blocks provide as much thermal insulation as double-paned windows. The mortar or silicone between the blocks and the insulation between the glass block window and the wall blocks air infiltration even better than traditional window frames. For optimal energy efficiency, look for glass block windows that carry the Energy Star label.
Privacy – The thick glass and multiple joints of glass block windows offer more privacy than standard glass panes. For even greater privacy, look for blocks manufactured with texture patterns designed to obscure the view from outside.
Lighter, more transparent patterns give you a good view outside without letting every passerby see in. A heavily textured pattern that almost completely obscures the view lets you maximize privacy for your bathroom, garage, basement, or front door sidelights.
Keep in mind that color, outlines, and some larger details are still visible even through heavy textures. If privacy is a priority, check the glass’ transparency before you buy.
Safety and security – By obscuring the view, glass block windows prevent opportunistic thieves from spotting your valuables. The thick blocks are more like masonry than like windows, so they can’t be broken through without a lot of noisy work that draws attention. They’re more waterproof than standard windows, helping to keep your valuables safe from storms and floods. Even bullet-proof models are available.
Heat buildup – Despite their overall energy efficiency, glass block windows can create a greenhouse effect that heats up the room. That’s a plus in a cold climate, where glass blocks help you make the most of the winter sun for heating.
In a climate with hot summers, though, this kind of window can make it hard to keep a room cool even with air conditioning. The effect is particularly pronounced in small rooms. Adding a reflective coating helps cut down on heat gain somewhat.
Reduced ventilation – Because glass block windows don’t open, they don’t provide the airflow standard windows do. That can be a problem in a bathroom or basement where humidity is an issue. Installing a hopper vent allows for ventilation without compromising the window’s energy efficiency, but this still gives you less airflow than you’d get from a fully operable window.
Installation issues – Glass blocks are heavy, and they sit directly on the wall. Before you build, you’ll need to be sure the wall and floor can support this weight. For this reason, it’s much easier to install glass blocks when the wall is being built.
Replacing an old window with glass blocks requires removing the window frame and possibly reinforcing the wall and floor. If you decide to go back to standard windows, you’ll need to replace the window frame.
When to DIY and When to Call a Pro
As a rule, experienced DIYers can handle smaller interior jobs such as adding a glass block window to a partition wall or building a glass block shower wall, wet bar, or kitchen backsplash. Installing an exterior window is a more complex job that should be left up to a professional experienced in working with glass block.
If you’ll be doing the job yourself, start by assessing the floor and wall’s ability to bear weight and adding structural supports if needed. Skipping this step could leave you with a sunken floor or collapsed wall. Next, carefully measure the space where you want to install the glass blocks. Leave around 2 inches free around the edges to account for the mortar, and remember to account for additional inserts, such as block vents and hopper windows.
If you can find a pre-made glass block panel that fits the space you have, this will be the easiest way to go. A panel is installed as a single piece, but it’s still a job for two people.
For spaces pre-made panels won’t fit, you can build block by block. You’ll need not only the glass blocks and suitable mortar or silicone, but also panel reinforcers, panel anchors, and spacers. This method requires careful measuring and laying. First dry fit the blocks in place using spacers to ensure everything fits as planned.
Once you’re confident in your layout, start laying the blocks with mortar, plumbing each one as you go to make sure it’s level. Lay two rows of blocks, wait around half an hour, then tool the joints with a jointer. Let the mortar harden for another half hour before you add another two rows. The weight of more than two rows can press unhardened mortar out of the lower sections.
After a week, the mortar should be set. If your new feature will be exposed to water, apply a silicone grout sealer to protect the joints.
More than just a decorative accent, glass blocks bring real value by improving your lighting, privacy, and security. While exterior windows are best handled by a professional, interior features are something you can do yourself either with pre-made panels or individual blocks.