Like many product categories the installation options for glass block windows have grown proportionately to the expanding design options. Years ago, blocks were made in a 8” x 8” x 4” size in a few patterns and put together inside a masonry window opening (usually by a skilled mason) block by block with a gray mortar and masons sand – not real sexy, but it worked. In today’s world people want to use blocks more creatively in different types of openings (could be masonry, framed, steel openings etc.) for a wide variety of uses, and not have to rely strictly on a mason to get the job done. The following 5 installation steps can help you think through what’s needed to have your block window installation project go smoothly.
- Step 1 – Ask, “What size is my window opening?” – The size of the opening is a large factor in the window installation approach. There are two basic ways to install a glass block window:
- (Option 1) As a window panel alone, or as a panel built into a vinyl or metal framed window system.
- (Option 2) installing the glass blocks one by one inside of the opening.
A benefit of glass block is it’s a heavy material, the challenge is it’s a heavy material when you’re installing it! For most openings less than 25 square feet consider option 1, the block window built as panel (or section) vs. option 2. Option 2 is usually more difficult, costly, and requires a higher skill level. For the first option you can get a block window panel built by a glass block window manufacturer, often saving time and money.
- Step 2 – Ask, “Where is this block window going?” A key factor in the block window installation is if the glass window is going in new construction or a remodeling project, and whether the surrounding construction is masonry (poured concrete or concrete blocks) or frame (surrounded by wood). Here are some recommendations for each job condition:
- New construction projects in framed openings – For new construction framed openings use a vinyl framed nail in glass block window. Consult your glass window manufacturer for the size to create your rough framed opening. These windows (which are usually siliconed together for an all glass look) can be purchased with nailing fins to simply nail in from the outside just like a traditional vinyl window in new construction. Since they can be manufactured with the 2” thick series of blocks (in either a high privacy “Ice” pattern or “Wave” pattern from Mulia Inc.) they are lighter than traditional block windows. These windows can also be purchased for the 3” and 4” thick series of blocks as well if you’d like to try one of the upscale designed Beveled or Spyra series of blocks from Pittsburgh Corning.
- New construction projects in masonry openings – For most masonry openings under 25 square feet it is best to purchase mortared or siliconed block panels that can be set into the opening and mortared in at the top (also called the head), sides (also called the jambs), and bottom (also called the sill).
- Remodeling projects in framed openings:
- (Option A) If you can adjust your openings to fit one of the vinyl framed glass block windows you can install your project like a standard vinyl replacement window (make sure the window manufacturer takes the window nailing fins off for this type of installation) by placing the vinyl window in the opening, insulating around the window, and installing aluminum coil stock capping to meet the glass block window.
- (Option B) If you can’t adjust your existing wood opening then remove the existing window sashes and mortar the glass block into the wood opening and install aluminum coil stock to the block and caulk where the coil stock meets the glass masonry units.
- Remodeling projects in masonry openings (concrete blocks or poured walls) – In remodeling projects measure the entire size of the masonry openings with the existing frame being removed (the only time you don’t remove the metal or wood frames is when the frame is either seated over the concrete blocks or poured walls and removing them might cause damage to the surrounding interior or exterior walls). Then size your block window panels to be smaller than the masonry openings (these block windows can be sized basically in any 2” size increment). The window panels can then be mortared into the openings.
- Step 3 – Ask, “What should I use to put the glass block together into a window panel assembly?” – You might have heard varied opinions about how the block panel should be assembled (the most common methods are using mortar or silicone). While some companies may tell you that only one method is correct, they are often just trying to get people to buy the fabrication method they prefer. You should choose that method where the panel size is going to fit best into the opening (making sure the joints do not exceed 1” around the window). Included below you’ll find some advantages of both the mortar and silicone systems:
- Advantages of Mortar over Silicone – Mortar is the traditional way to build a block window. The advantages of this system are the ability to vary the size of the mortar joint (helpful when you have an odd size), the mortar joints can be finished to match the existing masonry, and it’s very difficult to break a block out of mortared joint.
- Advantages of Silicone – Silicone is preferred if you like an all glass look to your panel, or if you need a smaller window in an opening (silicone joints are smaller than mortar joints), and transportation is safer because the glass window will stay together better than with mortar.
- Step 4 –Ask, “How do I handle an opening greater than 25 square feet?” – When openings become larger than 25 square feet (mostly in commercial, architectural and institutional projects) it is often better to build the window block by block within the opening (this is because the panels would need to become larger, heavier, and are more difficult to handle). With openings of this size you will need to keep the following installation points in mind:
- The window usually requires a “soft joint” at the top (head), and sides (jambs) of the opening – Windows greater than 25 square feet need more space for expansion and contraction requiring glass block caulk be used at the jambs and head of the opening along with an expansion strip. For larger openings an aluminum channel will also help with concerns regarding wind loads.
- Structural steel or aluminum may be required – To allow for wind loads and structural safety larger openings (greater than 20 feet high for 4” blocks and 10 feet high for 3” blocks, and 25 feet wide for 4” blocks and 15 feet wide for 3” blocks) there should be a metal stiffener put into the glass block window. This stiffener could be a metal hidden plate, an I beam, or a T shaped mullion of steel behind the window/wall.
- Step 5 – Ask, “What should I do if my skills or physical abilities don’t allow me to do this type of installation?” – Call a specialty glass block contractor or find a nationwide glass block window manufacturer (to make a pre-made glass panel) to make contract out the installation of this window. This will ease the process, reduce cost, and improve the quality of the block window installation project.
Now that you’ve got the 5 installation steps you’re ready to either to get your hands dirty or hire the right specialty glass block contractor for your project.
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Mike Foti is President of Columbus Glass Block, Cleveland Glass Block, Mid America Glass Block Cincinnati, Dayton, Akron & V.P. of Eastern Glass Block New Jersey and New York - suppliers, glass block window manufacturers, and glass block contractors. Tel. 614-252-5888 Nationwide 877-668-5888 firstname.lastname@example.org
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