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Installing Glass Block Windows

Installing windows made of glass block from Pittsburgh Coming Corporation is a simple project. In fact, it's as easy as laying cement blocks. All that's required to do a professional- looking job are a few basic tools, a little planning and your favorite glass block from Pittsburgh Coming.

Even though the project is simple, there are some "tips" to doing a good job that you should know before you start the job. We suggest you read this pamphlet thoroughly and plan to follow the installation steps as closely as possible.

Pre-Installation Points

You maybe tempted to start the job by quickly tearing out your old windows. We don't blame you since you're going to replace them with energy-saving, easily-maintained, secure Pittsburgh Coming glass block. But first, there are a couple of things to do.

Measure each window opening

While the old windows are still in, measure the height and width of each total opening. Measure the openings as though the old windows, frames and all other obstructions had already been removed.

Make a list of all window sizes

Space is provided on the back page of this brochure for listing all window sizes. Number each window and cross reference that number to the list.

Take the list to your Pittsburgh Coming glass block dealer

Your dealer will help you select the glass block size that will best accommodate your window openings. Your dealer can also help you select the glass block pattern which will provide the amount of privacy and light transmission you prefer.
Allow for mortar joints. Be sure to allow for a 1/4 -inch mortar joint around all four sides of each glass block, including a joint between the glass block and the window opening.

Before you start

We suggest you have all the Pittsburgh Coming glass block you need delivered before you start to remove the old windows.

Tools and Material

The best way to keep a glass block installation project simple is to have the right tools and material on hand. With one or two exceptions, all the items required to install glass block windows are found on the average home work bench.

  • Hammer
  • Chise
  • Crowbar
  • Trowel
  • Pre-mixed mortar
  • Striking Tool
  • Level

If installing glass block windows in a wood frame opening, the following items will also be needed:

  • Caulking gun
  • Wood molding
  • Wood preservative


Remove the old windows

You've made your preparations and glass block are on hand. Now you're ready to start the actual work by tearing out the old windows.

Old windows are constructed with wood, steel or aluminum frames. Wood and aluminum frames are very easily removed using a claw hammer or

  • crowbar. Steel frames may require cutting with
  • hacksaw. Whatever the case, entirely remove the old frames.

"Level" the windowsill

You may find that old windowsills are not level because of high spots or slumps. In either case, it will be necessary to level the sills so that the glass block will fit properly in the window openings.

In the case of high spots, use a hammer and chisel to chip away the old mortar. If the sills slope to either side or the middle, the first bed of fresh mortar will level them out. Remember, the first bed of mortar is part of the overall window opening measurement.

Take a "reading" of glass block placement

Before actually mortaring the glass block in place, make a "test run." Place loose block in each window opening to create one complete horizontal and one vertical row. Place folded cardboard or wood spacers between the glass blocks to simulate even mortar joints. Once you have a complete horizontal and vertical row in place, put check marks on the wall surrounding the window opening to line up with the top and bottom of each spacer.

By setting the block in loosely, you have the opportunity to make whatever changes are necessary for problem-free installation.

Put check marks on the wall to line up all joints when mortaring in glass blocks.

Mortar preparation

Preparing mortar is an important step when you install your glass block windows. Mortar consistency must be workable but dry enough so that the glass block won't "float" out of place causing uneven joints.

As a rule, mortar which has the consistency of bread dough will produce the best results. Any commercial, pre-mixed dry mortar will be adequate. Follow the directions on the sack and prepare approximately one bucket of mortar for each window. If you prefer, make your own mortar using a mixture of one part masonry cement and three parts sand.

Installing glass block windows in masonry openings

Put a layer of mortar on the windowsill and smooth it out with a trowel to create an even "bed." Then put a layer of mortar on the side of the opening where the first block will butt against the wall. Put mortar on one vertical edge of each block at a time and place them in position to create the first row.

Make sure that the first row is even to the eye or check it with a level. Remember to position each glass block row so that all mortar joints line up with the check marks on the wall. Put a bed of mortar across the top of the first row making sure that all spaces between the glass blocks are filled. Repeat the process for each new row until all blocks are mortared in place and the window is complete.

If the blocks "sink" or "float," mix some dryer mortar to create more substantial joints. You can firmly press the tops of the blocks with your hand or the trowel handle to line them up.

Ventilator Installation

If you're installing a ventilator in a window, simply mortar it in place of one or more glass block, depending on the size of the unit you want. Generally, ventilators are positioned in the center of the window for aesthetic reasons. When considering a ventilator, plan to use a unit which is large enough to meet your air flow requirements. Ventilators are available in various sizes from your Pittsburgh Corning glass block dealer.

Smooth all mortar joints

Let the glass block windows "settle" for approximately two hours or until the mortar is almost dry. Then smooth all joints to remove excess mortar for a clean, professional-looking job. The smoothing procedure will also compact the mortar to create a moisture-proof seal.

By using a striking tool on all mortar joints, the installer creates a professional-looking effect on glass block windows.

Clean the glass block windows

Allow the windows to set long enough for all mortar joints to "firm up." Then wipe off excess mortar using a cloth and some water. Be careful not to let excess mortar totally dry before attempting to clean the window surface. Do not use steel wool or other abrasive materials to remove partially dried mortar.

Installing glass block windows in a wood frame opening

Installing glass block windows in a wood frame opening is as simple as the process for any other structure. However, there are a few special installation procedures that should be followed to insure a complete and adequate job.

Before installing the glass block, apply a coating of preservative to all the exposed wood frame area around window openings. Then, when you start to put in the block, USE MORTAR BETWEEN THE GLASS UNITS ONLY. DO NOT USE MORTAR BETWEEN GLASS BLOCK AND THE WOOD FRAME. Glass blocks should be shimmed in tight to the frame.

To complete the job, fasten wood molding to the house frame so that it overlaps the glass blocks approximately 1/2" and holds them in place. Caulk wherever glass blocks butt against the trim on both interior and exterior surfaces.