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Glass Block Windows iStock

Glass block is a popular choice for bathrooms, and it’s easy to see why. Rather than partitioning spaces between the sink, toilet, and shower or tub with dark walls that can make the room feel claustrophobic, keep the light as well and add some privacy. If you replace one or more of the solid walls with glass block walls or windows, you can transform a tight space into a bright space — without sacrificing privacy.

Glass block can be used in several ways in the bathroom. Glass block windows are available in a limited number of sizes, and can be installed in a bathroom’s exterior wall. It’s much easier to install them during new construction, as opposed to removing an existing window and replacing it with a glass block version.

That’s why most homeowners choose to hire an experienced contractor for this kind of retrofit. But DIYers can handle installing a glass block window in a partition wall, or building an interior wall with glass block. In this article, I’ll lay out the tools and materials needed, and the techniques required to work with glass block.

Before You Build with Glass Block

Most glass block projects are constructed not unlike laying out a row of bricks and mortar. In fact, special glass block mortar mix is the industry standard for its ability to connect the blocks strongly and safely. If you prefer, for small spaces or just for the aesthetic appeal, you can choose to use glass block silicone between blocks.

To determine how many blocks you will need, or if you can use a pre-made block unit or kit, measure your space carefully before you begin. You’ll want to measure the width and height of the wall or window in several spaces, in case the existing space is not 100% plumb and level. Take the shortest of each measurement as your height and width. Because you’ll be putting mortar or silicone between the blocks, you’ll want the opening to be about one-half to 2-inches larger than the total measurement of the glass blocks.

To compute your materials, know that the average glass block measures either 7.75- x 7.75-inches or 5.75- x 5.75-inches. Compare your measurements to decide what size of block you’ll need, and also any additional inserts, like block vents, sometimes used in glass block windows. Check for pre-made glass block kits at your local hardware store that may come in the dimensions you require, or purchase glass blocks and materials individually.

See “Tools and Materials Needed” located at the bottom of this article.

How to Install a Glass Block Wall

  1. Using a bucket, water, and a mortar and grout mixer (or a sturdy stirring stick), mix together your glass block mortar mix according to the package’s directions. (This mortar mix is specifically designed to use with glass blocks, and contains a mix of mortar cement and white sand.)
  2. You can use a pre-made glass block frame to begin, or start with a layer of mixed mortar. With a trowel, spread a light layer of mortar on the bottom of the glass block area. You want the mortar to be somewhat firm, like bread dough, to support the weight of the glass blocks.
  3. Starting with the bottom row, apply a small amount of mortar to the sides of each block and put them in place, starting at one corner or edge. If desired, use glass block spacers at each block joint to create even spacing between blocks. (You’ll remove these spacers later and fill in the gaps with mortar or silicone to complete the seal.)
  4. With each new block mortared in, check that the blocks are level both vertically and horizontally before proceeding.
  5. Continue with each block, row by row, working up to the top.
  6. For the last row, pack mortar on the top as well, and smooth. Mortar in the sides of the glass blocks as needed. Remove any temporary spacers and fill in gaps with mortar.
  7. Clean up any extra mortar or silicone with a damp cloth.
  8. When your mortar has dried and set (24-48 hours), you can complete the job by applying a silicone sealant designed for glass blocks along the outer edges.

Tools and Materials Needed

  • Glass blocks
  • Glass block vent or screen panel (if using)
  • Glass block mortar mix
  • Mortar and grout mixer
  • Glass block silicone (for finishing, or as mortar, if desired)
  • Disposable gloves
  • Brick trowel
  • Glass block vertical and horizontal spacers (optional: wooden shims for bottom row leveling)
  • Tape measure
  • Level
  • Cleanup rags
  • Mixing bucket