Glass block windows bring privacy, light, and a clean look to basements, bathrooms, and entryways. Silicone can help seal glass blocks and hold a small, non-load-bearing installation in place. But the method must match the project.
A glass block window is not the same as a brick wall or structural opening. Large openings, exterior walls, basement windows, and projects that change the size of an opening may need professional masonry work. When in doubt, ask a licensed contractor to inspect the area first.
At Casey Tuckpointing, we have served Chicago and nearby suburbs since 1994. We are a family-owned and operated masonry company. We handle glass block window repair and replacement, brick repair, waterproofing, and related masonry work. We also offer free estimates.
When Silicone Works for Glass Block Installation
Silicone works best for small glass block projects where the blocks do not support the building. A common example is a bathroom window or a small basement window set inside a sound frame. The opening must remain stable, level, and dry.
Silicone creates a flexible seal between the blocks. This helps the installation handle small movements caused by temperature changes. It also helps keep water and air out when you apply it correctly.
Silicone alone may not provide enough strength for every project. Large windows, exterior openings, and walls exposed to strong wind may need a mortar system, a special glass block channel, reinforcing materials, or professional framing. Do not use silicone to repair a failing wall or support a damaged lintel.
Chicago’s freeze-thaw cycles can place extra stress on exterior masonry. Water enters small gaps, freezes, expands, and then weakens the surrounding materials. For a glass block opening on an exterior wall, proper drainage and weather protection matter as much as the seal itself.
Tools and Materials You Need
Gather all materials before you begin. A clean work area helps you avoid gaps and uneven joints.
- Glass blocks sized for the opening
- Exterior- or interior-rated glass block silicone, based on the project location
- Glass block spacers or a manufacturer-approved installation system
- A caulk gun
- Level
- Tape measure
- Rubber mallet
- Utility knife or scraper
- Clean rags
- Mild cleaner and water
- Painter’s tape
- Shims
- Backer rod or approved filler for large gaps
- Safety glasses and work gloves
Read the silicone label before use. Some products work only indoors. Others are made for windows and exterior exposure. Do not use a product that the manufacturer does not approve for glass, masonry, or the conditions around your opening.
Measure the opening in several places. Old masonry openings may not be square. Record the narrowest width and height. Leave the gap required by the glass block system. Blocks should not fit so tightly that the frame or wall presses against them.
Prepare the Opening
Remove the old window, loose sealant, broken mortar, dirt, and paint from the opening. Scrape away material that prevents the new seal from touching a clean surface. Do not damage sound brick or the frame while removing old material.
Check the sill, sides, and header. The sill should be solid and level. The side walls should not move when you press them. Look for cracks, water stains, rust, loose brick, or crumbling mortar.
Water infiltration through deteriorated mortar joints is one of the leading causes of structural damage in brick buildings, according to the Brick Industry Association. If you see water damage around the opening, solve that problem before installing new glass blocks.
Clean the surfaces with a mild cleaner and let them dry fully. Silicone will not bond well to dust, loose mortar, standing water, or oily residue. If the opening needs masonry repair, our glass block window repair and replacement services can help you plan the work safely.
Use shims to correct a small uneven area only when the installation system allows it. Do not use piles of caulk to level a badly damaged sill. A weak or sloping base can cause the blocks to shift and crack the seal.
How to Install Glass Block With Silicone
Follow the instructions from the glass block manufacturer first. Product systems differ. The steps below describe a common small installation.
1. Dry-fit the blocks
Set the blocks in the opening without silicone. Use spacers if the system requires them. Check the pattern, joint width, and overall fit. Make sure the blocks sit flat and that the finished surface will line up with the surrounding wall or frame.
Mark the block positions if needed. This step helps you find problems before the silicone begins to cure.
2. Apply the first silicone bead
Remove the dry-fit blocks. Apply a steady bead of silicone along the sill or channel. Keep the bead thick enough to create full contact, but do not overfill the joint. Too much silicone can push the blocks out of line and create a messy finish.
Work in sections that you can complete before the product skins over. Silicone begins to form a surface film quickly. The label will tell you how long you have to tool the joint.
3. Set the first block
Place the first block into the wet silicone. Press it down gently. Do not twist it. Check the level from front to back and side to side.
Add the required spacer. Apply silicone to the next vertical joint and set the next block. Keep checking the level as you work. Small errors at the bottom can grow across the entire window.
4. Build each row
Continue across the first row. Keep the joints even. Remove excess silicone with a scraper or tool while it remains workable. Avoid smearing it across the face of the blocks.
Apply silicone to the top of the first row before setting the next row. Place each block carefully. Check the level after every few blocks. Use only light pressure. Glass blocks can chip or crack if you strike them too hard.
Some systems need reinforcement or horizontal supports between rows. Use the materials and spacing listed by the manufacturer. Never guess when the window is large or exposed to weather.
5. Finish the sides and top
Apply silicone along the side joints and the top joint. Press the sealant into any approved gap between the glass block panel and the frame. Keep the joint smooth and complete.
If the opening has a large gap, use the correct backer material first. Do not fill a deep gap with one thick layer of silicone. A deep bead may not cure properly and may pull away from the sides.
6. Tool the joints
Tool the silicone with a clean tool or a gloved finger, following the product directions. Make the joints slightly concave or use the shape recommended by the manufacturer. Smooth the surface before it skins over.
Remove painter’s tape right after tooling. Pull the tape away slowly at an angle. Clean small smears with the product-approved cleaner. Do not use a harsh solvent that can damage the frame, finish, or glass block.
7. Let the installation cure
Keep the panel still while the silicone cures. Protect it from rain, impact, dust, and freezing temperatures. Cure time depends on the product, bead size, temperature, and humidity.
Do not wash the window, hang items from it, or press on the blocks until the label says the seal has cured. A surface that feels dry may still be soft below the surface.
Common Mistakes to Avoid
A glass block installation can look simple, but small mistakes may lead to leaks or movement.
- Using indoor silicone on an exterior window
- Installing blocks over loose brick or rotten framing
- Skipping the dry fit
- Failing to check the sill for level
- Leaving dust or water on the bonding surfaces
- Applying a bead that is too thin or too deep
- Pressing blocks together without the required joint space
- Leaving gaps at the corners
- Using silicone to cover a structural problem
- Ignoring water stains around the opening
- Cleaning cured silicone with a sharp tool that scratches the glass
Do not remove a lintel, beam, or support above a window without a proper plan. A damaged steel lintel can cause cracks and sagging masonry. Our masonry contractors in Chicago can inspect the surrounding brickwork and explain the repair options.
Should You Install Glass Block Yourself?
A small interior project may suit a careful homeowner who can follow the product instructions. You should understand the limits of the work. Silicone installation does not replace structural repair, waterproofing, or code review.
Call a professional when the opening is in a foundation wall, the wall shows movement, the blocks are part of a large exterior panel, or the area leaks. You should also get help when the opening needs brick removal, lintel work, or a new support.
Property managers and condo associations should keep records of repairs and inspections. A masonry contractor may need to coordinate access, permits, and related work. Casey Tuckpointing works with homeowners, management companies, general contractors, architects, realtors, and condominium associations.
We do not subcontract our masonry work. Our licensed and fully insured team manages the project and provides follow-up service when needed. Our founder, Kazimierz Sieracki, built the company around hands-on European masonry craftsmanship and careful modern methods.
Protect the Glass Block Window From Chicago Weather
A new window still needs regular care. Check the silicone joints at least once a year. Look for peeling, gaps, cracks, or areas where the seal has pulled away from the frame. Inspect the surrounding brick and mortar as well.
Keep gutters, downspouts, and flashing in good condition. Water from the roof or wall can reach the window even when the glass block panel looks sound. If the surrounding masonry needs protection, our Chicago waterproofing services can help identify the source of the moisture.
Do not paint over failing silicone. Remove the damaged sealant, clean the surface, and use a compatible replacement product. If the wall has widespread cracks or crumbling joints, repair the masonry before resealing the window.
Glass Block Installation and Repair in Chicago
Glass block work often connects to other masonry problems. The opening may need brick replacement, tuckpointing, lintel repair, caulking, or waterproofing. Treating only the visible gap may leave the cause untouched.
Casey Tuckpointing has served Chicago, Skokie, Evanston, Glenview, Norridge, Lincolnwood, Elmwood Park, and surrounding suburbs since 1994. We are licensed, fully insured, and family-owned. Our business has a 5.0 Google rating with 86+ reviews. References are available upon request.
We offer a free estimate so you can understand the condition of the opening and the work involved. Call (847) 962-6309 to speak with us, or request a free estimate online.
You can also reach us at info@caseytuckpointing.com or visit us at 3637 N Luna Ave, Chicago, IL 60641. We are open Monday through Friday from 7 AM to 6 PM and Saturday from 7 AM to 2 PM. We are closed Sunday. Our Google profile, Yelp page, and BBB profile provide more ways to learn about our work.
A careful silicone installation can seal a small glass block project, but a safe, lasting result starts with a sound opening and the right materials.