Adding a glass block window is a great way to let light into a space while maintaining privacy. Glass block windows look stylish and can increase security. Installing a glass block window is also a relatively easy DIY project for many homeowners. Following some key steps will ensure the glass block window is properly installed and functions as intended.
Benefits of a Glass Block Window
There are several benefits that make a glass block window an excellent choice:
- Privacy – The thick glass blocks obscure vision so people cannot see directly into the window. This allows light in while maintaining privacy.
- Security – The glass blocks are thick and durable. Combined with mortar, they create a window that is more difficult to break through than a regular window pane.
- Light – Glass blocks allow an ample amount of natural light to filter into a space. This can help brighten up interior rooms.
- Insulation – Glass block windows provide an extra layer of insulation, helping keep interior spaces comfortable.
- Style – The grid pattern of glass blocks has an attractive, contemporary aesthetic. Glass block windows can enhance a room’s decor.
For bathrooms, basements, and other spaces where you want light along with privacy and security, a glass block window is an ideal solution. The installation process takes some time and care, but it is a DIY-friendly project for many homeowners.
How to Install a Glass Block Window
Installing a glass block window involves removing the existing window, preparing the opening, installing a metal framework, adding mortar, and setting the glass blocks. Here is the complete process:
Select a Window Location
Choose an appropriate location for the glass block window. Consider the room layout, existing windows and doors, and lighting needs. Bathrooms, basements, and first-floor interior walls are common locations. Avoid above countertops or sinks, where sealing is difficult.
Glass block windows come in standard sizing, usually between 16” and 24” wide and 20” to 32” high. Measure the existing window or desired opening to determine what size glass block window to purchase.
Ensure the selected location has a wood or metal frame in good condition to support the glass block window.
Remove the Existing Window
Carefully remove the existing window and its trim work:
- Use a utility knife to cut through any exterior caulk or paint sealing the window in place.
- Remove any screws, brackets, or other fasteners. Label pieces for reinstallation.
- Detach the interior trim work with a pry bar. Remove any remaining nails and set aside.
- Remove the window sash and frame. Scrape away old caulk and debris.
Make sure the rough opening is in good condition for installing the new glass block window. Verify it is plumb and level.
Prepare the Opening
The opening must be properly prepared and have the right materials in place to support the glass block window:
- Ensure the sill plate is secure. Add bracing if the sill plate is loose or damaged.
- Check that the opening has proper jack studs at the sides.
- Seal any gaps around the rough opening with silicone caulk.
Install the Metal Framework
Glass block windows require a metal framework around the perimeter to provide sturdy support:
- Measure the opening and cut metal channel frame pieces to fit with a hacksaw.
- Apply silicone caulk to the back of the metal channels.
- Attach the side jamb channels first with appropriate metal fasteners, keeping the channels plumb and level.
- Install the sill channel, shimming if necessary to ensure it is level.
- Attach the header channel across the top to complete the metal frame.
Waterproof the Window Sill
Since the glass blocks will not form a water-tight seal, it is critical to waterproof the window sill:
- Clean and prepare the sill with sandpaper. Vacuum up any debris.
- Apply a bead of silicone caulk along the edges where the sill meets the side jambs.
- Cover the sill with peel-and-stick waterproof membrane. Cut it to overlap up the side jambs.
- If desired, top with additional waterproof layers, such as ice and water shield.
Properly waterproofing the sill helps direct water to the exterior and prevents leaks.
Install Expansion Strips
Expansion strips around the interior perimeter allow room for the mortar to expand:
- Cut cork, foam, or rubber strips to fit inside the window openings.
- Apply silicone caulk to one side and stick them in place on the interior side.
- Keep them 1/4” to 1/2″ away from the wall surface.
Mix and Apply Mortar
Glass block mortar differs from regular mortar. Use a glass block mortar mix:
- Prepare mortar per package directions, to a grainy, damp, loose consistency.
- Load some mortar into a mortar bag to control application.
- Apply a layer of mortar onto the back side of each glass block.
- Also apply mortar to the sill, jambs, and header, about 1/4” to 1/2” thick.
Mortar adhesive is necessary for proper glass block installation.
Set the Glass Blocks
Carefully set each glass block into place:
- Set the first row of blocks on the sill, pressing gently into place. Use spacers between blocks.
- Apply mortar and set the second row. Check alignment with a level.
- Continue setting rows until reaching the top. Remove excess mortar with a trowel.
- Allow the mortar to begin curing before moving to the next steps.
Go slowly to keep the glass blocks aligned and prevent slipping.
Mortar the Exterior
Properly mortaring the exterior gaps will help seal the window:
- Load mortar into the mortar bag. Trim the opening so it is narrow.
- Starting at the bottom, fill the exterior gaps between blocks and metal frame with mortar.
- Slowly work your way up both sides, then across the top.
- Strike and smooth the mortar with a tuck pointing trowel for a clean finish.
Install Exterior Trim and Seal
Adding trim gives the glass block window a finished exterior look:
- Measure and cut exterior trim pieces for each side from lumber or pvc.
- Apply silicone caulk to the back of trim. Press trim firmly against the exterior wall around the glass block window.
- Caulk around the edges of the trim. Use a wet finger to smooth the caulk for a clean look.
- Allow the caulk to fully cure for several days before exposing to weather.
Install Interior Trim
Interior trim gives a tidy, polished look:
- Reinstall any original interior window trim, jambs, and casing that was removed. Use scrap lumber to replace damaged/missing pieces.
- Install trim snugly against the glass block window, leaving expansion strips visible.
- Fill nail holes with wood filler and touch up with paint to match the wall.
With both interior and exterior trim installed, the glass block window installation is complete!
Finishing Touches
Adding a few final touches will complete the project:
- Make sure all silicone and mortar are fully cured, typically taking 5-7 full days.
- Placing sheer curtains over the window allows extra privacy while retaining light.
- Windows can be decorated with trim pieces, frosted film, or other treatments.
- Caulk around the interior trim edges for an air tight seal.
For added energy efficiency, consider low-emissivity coatings and thermal pane options.
Glass Block Window Variations
There are a few variations and customization options when installing a glass block window:
- Vented glass blocks – Special blocks with internal louvers can allow ventilation. These help prevent condensation in humid areas like bathrooms.
- Curved windows – Convex curved glass blocks are available for a rounded window. The installation process is largely the same.
- Color options – Glass block windows can incorporate colored blocks or be frosted for decoration. Clear blocks maximize light.
- Custom shapes/sizes – For unique openings, full glass blocks can be cut with a wet saw to fit odd dimensions. Special corner blocks are also available.
Advantages of Hiring a Professional
While a DIY glass block window installation is possible, it has some challenges. Hiring a professional window installer is advisable in some cases:
- For large or complex window openings, a professional can ensure it is structurally sound.
- Experts have specialized tools and materials to make the job easier. This includes laser levels, high-strength mortar, and vacuum suction cups for handling blocks.
- There is less margin for error. Mistakes like cracked glass blocks or crooked rows are expensive.
For homeowners less comfortable with construction projects, hiring a professional may provide peace of mind and better results.
How to Install a Glass Block Window for Extra Privacy: FAQ
Here are answers to some frequently asked questions about installing glass block windows:
How long does a glass block window installation take?
The project will typically take 2-3 days from start to finish. Removal of the old window and modifications to the opening take 4-6 hours. Installing the metal frame, mortar, and blocks requires 6-8 hours. Allow another 4 hours for trim, caulking, and sealing the window. This timeframe can vary based on window size and whether doing it yourself or hiring a professional.
Can you install a glass block window in an existing wall?
Yes, it is possible to install a glass block window by cutting an opening in an existing wall. Extra framing and structural preparation are required to ensure the wall can properly support it. Consult a building professional to evaluate feasibility for specific cases.
Do glass block windows open?
Glass block windows are fixed and do not open like traditional windows. Glass block windows provide light while maintaining privacy and security. For rooms requiring ventilation, use vented blocks or install a glass block window alongside an operable window.
How much does a glass block window installation cost?
A typical professionally-installed glass block window costs $800 – $2,000, with most homeowners spending $1,200 – $1,500. DIY installation using purchased materials lowers costs to $300 – $800. Window size, customization, labor rates, and material grades affect the overall project cost.
What is the best method to clean a glass block window?
Use a mild soap and soft cloth to clean glass block windows. Avoid abrasive cleaners. For hard water spots, wipe with equal parts white vinegar and water. Rinse thoroughly and use a squeegee to remove moisture. Avoid cleaning glass blocks in direct sunlight, which can cause streaking.
Conclusion
Installing a glass block window is a worthwhile upgrade that provides increased light, security, insulation, and privacy. With careful planning and preparation, both DIYers and professionals can successfully tackle a glass block window installation project. Following the step-by-step process will help ensure proper installation so the glass block window functions as intended for many years.