Q&A / 

Glass Block Installation

glass block installation

Glass block installation like this requires skill. I doubt you'll do a job like this your first time. Copyright 2018 Tim Carter

"Now for the fun part. I hope you bought several bundles of cedar shims, as we are going to need them."

Glass Block Window Installation Tips

  • Take great measurements - mortar gap on sides and top can be up to 3/4 inch
  • Use ingenuity to remove the old window frame
  • WATCH glass block videos below
  • Wood shims hold new pre-made glass block window in place
  • CLICK HERE to Get Tim's FREE & FUNNY Newsletter!

Can You Buy Pre-made Glass Block Windows?

Yes, that's the easiest way to install glass block windows. Don't try to lay glass block like a bricklayer lays brick. It's very easy to install a pre-made glass block window, but hard to install individual glass blocks.

Glass block windows are a fun project to tackle. Minimal tools are needed. If all goes well even a "newbie" DIY'r can install four pre-fabricated glass-block windows in a day. Here is what I have learned over the years about installing these neat windows.

Related Links

 Glass & Acrylic Blocks Do Many Things

Glass Block

Glass Block Manufacturers

Glass Block Greenhouse

Should I Make a Drawing of the Existing Opening?

Make a simple sketch of each window opening you intend to transform into the glass block. Measure the narrowest point side to side and up and down to the masonry or where you "think" the masonry will be once you remove the frame.

If you're in doubt, take a photo of different windows. You will need to show these to the company that will make your glass block panels. Check your measurements.

Go to the fabricator and ask if everything is in order. Show him/her using your photos and drawings where the measurements were taken. Getting the right size is the most critical aspect of the ENTIRE job. Let's take our time and do this right.

Free & Fast BIDS

CLICK HERE to get FREE & FAST BIDS from local glass-block window installers. Ask about venting windows.

How Big Will the Glass Block Window Be?

When the windows are built, they will be a giant slab of glass. Some fabricators put a band clamp around the windows so they can't break apart. If you don't have a clamp, be CAREFUL! If you bump a corner, you can pop a glass block off. Ask the fabricators to wrap the windows with a band clamp if possible.

Glass Block Videos

Watch these two videos to give you an idea of how easy it can be to work with glass block. In these, I put together panels with a single block.

You can BUY pre-made windows so you don't have to do what I did in the videos.

How Heavy are Glass Block Windows?

The glass block windows are very heavy. Glass block is just clear rock believe it or not. It's pure silica in most instances. Just one square glass block can weigh three or four pounds.

If you're doing a glass block window installation, one complete window can weigh 60, or more, pounds,

What is the Hardest Part of Glass Block Installation?

Removing the old window and frame is the hardest part of the job. If you get the frame out easily, celebrate!

If your window frame is a full-width metal frame that was cast with the concrete, then you better ask the fabricator for his recommendation. I always leave those frames in place. It is a NIGHTMARE to remove them.

Once the old frame is out, use a brush to clean away dust and debris. I also recommend that you sweep up the floor and get all unnecessary stuff out of the way.

How Many Old Windows Should I Remove in a Day?

Remove as many frames and old windows as you think you can deal with in a day. I prefer to get all the demo work done and do things in stages. I don't like to do these windows one at a time. It really breaks up your momentum.

WARNING TIP: Do not remove an old window unless you're sure the new glass block panel is going to fit inside the opening.

glass block window installation

A large window like this needs to be installed one glass block at a time. It's a huge window. Copyright 2018 Tim Carter

How Much Mortar is on the Sides of the Window?

I also assume that there will be a 1/2 inch gap of mortar around the window. If so, then place several shims on the bottom frame that extend up 1/2 inch. Place these in from the corners about 3 inches or so. Slightly dampen the exposed masonry jambs with a spray bottle of water.

Now for the fun part. I hope you bought several bundles of cedar shims, as we are going to need them.

Where Do You Apply the Mortar?

Trowel some of the cement mortar onto the sill. Don't use bricklayers' mortar. Use Portland cement and sand. It will be stronger and more waterproof. If mortar is your only alternative, it will work, but I prefer cement.

Do You Install the Glass Block Panel on Shims?

Now tilt or slide the window onto the shims. Take two other shims and place them between the top of the window and the jamb. Slide them until they are just snug.

Check the window for plumb and square. You are also looking for equal reveal side to side. You want the window parallel with the inside and outside walls, not twisted.

CLICK HERE to get FREE & FAST BIDS from local glass-block window installers. Ask about venting windows.

How Do You Install the Mortar?

Use rubber gloves, small trowels, sticks, whatever it takes to pack the cement mortar around the window. Fill any pesky gaps at the bottom.

Should I Put Mortar On Top of the Glass Block?

Don't put any mortar on the top of the window. Downward pressure or stress over time can crack these windows. The top gap can be successfully filled with caulking tomorrow.

Your mortar may be too wet to tool as soon as you install it. Don't worry. Within a short period of time, the mortar will begin to harden. You can tool it with an old spoon, a stick, or with your fingers. Use a damp sponge to remove mortar smears from the glass.

When Can I Remove the Shims?

Usually within about two hours, you can gently remove the shims. Apply pressure against the glass as you pull the shims. Immediately, fill the bottom holes with cement mortar. Blend it in to match the texture and tooling of the rest of the joint.

When Do I Caulk the Top?

Don't try to caulk the glass on the same day it is installed. I get the best results waiting 24 hours. Don't try to fill the entire space with caulk!

Use a foam caulking backer rod to get within 1/2 inch of where the caulk joint will finish out. Use 100 percent silicone caulk. Wipe up smears immediately with lacquer thinner.

"Dear Tim,

I was looking at info about building glass block windows and you were talking about using lacquer thinner to clean up silicone residue. I thought I'd e-mail you to offer the suggestion that the next time you are using silicone you try denatured alcohol. My tile man taught me this and it works really really good! Probably less toxic too! I share your interest in building...I live in what was the Hartwell fire department at the turn of the last century and remodeled it into something a little more modern. " - John Figueras, Cincinnati, OH

Dear John,

Thanks for this tip.

Author's Note: We've received other questions with similar problems or questions. Here's one from Lena K. of Rockville, MD, regarding basement replacement windows.

"Our basement windows leak air as well as water when the snow melts. The house was built in 1965 and the windows seem to be from that time. They are below the ground level with wells dug out around them. They are set directly into concrete blocks. I looked at different replacement window manufacturers and installers, and none of the ones I saw offer specific windows for basements. Do you have any suggestions? (We aren't planning on doing the replacement ourselves). Thank you."


Companion Articles:  Glass & Acrylic Blocks Do Many Things, Glass Block, Glass Block Manufacturers, Glass Block Greenhouse

Column B395

Glass Block Installation - It's Not as Easy as It Looks
Article Name
Glass Block Installation - It's Not as Easy as It Looks
Glass block installation is not easy. Don't believe what you see on TV shows. You need skills and magic to get it right.
Publisher Name
Publisher Logo

13 Responses to Glass Block Installation

Leave a Reply

Your email address will not be published. Required fields are marked *