Glass Block Basement Window Installation Tips

February 1, 2015

If you need to replace your old, single-pane basement windows consider upgrading to Glass Block windows. Glass Blocks are weather-tight, maintenance-free, and are very energy efficient. With an R-Value of up to 2.0 glass blocks will help to keep your basement warm in the winter, an important consideration for those of us living in Illinois and other northern states.

Follow These Basement Window Installation Tips

Clear the Window Opening

Remove the old window being careful not to break the glass to avoid injury. Using a pry-bar or wrecking bar remove the old window jamb. You may need to use a saw to cut the wood at the four corners for a clean demo. Remove the window sill, the side jambs, and the head jamb. Using a hammer and chisel chip away at any remaining mortar and/or wood that may be left behind.

It’s important to have a clear opening where you will install your new glass block window. SAFETY FIRST: Be sure to wear your safety glasses for this step.

Accurate Measurement:

Carefully measure the opening so you can order your new glass block windows. Measure twice!!! Most glass block window fabricators can provide standard glass block assemblies in 1 inch increments. Be sure to subtract ½” per side from the physical measurement. So if your window opening is 25 inches tall x 37 inches wide; you should order a glass block assembly that is 24 inches high by 36 inches long.

Bring a Friend!!!

Larger assemblies of glass blocks can become quite heavy. Be sure to bring a friend along to help you carry your new block windows.

Temporary Wood Block

Attach a temporary block to the underside of the sill plate or joist. This will be used as a back stop to hold the top of the glass block assembly in the proper position and prevent the installer from pushing the window through the opening. Bad things will happen if you push your new windows through the opening and they fall through, crashing to the basement floor.

Apply Mortar

Mix a small batch of mortar in a pail or bucket. Use a small amount of water so the mortar will be somewhat stiff as opposed to very fluid. Prepare the mortar in small batches so it won’t setup in the bucket before use. Depending on the size of your project it may take one or two bags of mortar. Apply a thick layer or mortar along the bottom of the curb. Smooth the mortar with a trowel. CAUTION: Wear gloves for this step to protect your skin.

Set the Window in Place

Place the window on top of the bed of mortar. You may need a small ½” block in the two lower corners to maintain the height. Gently wedge a small block in the middle of both sides and the top of the window to keep the glass blocks in place while you apply the remaining mortar. Apply mortar along the top and both sides of the window using a mortar bag. Remove the temporary wood wedges and trowel the mortar smooth.

Tools Required:

  • Caulking Gun
  • Chisel
  • Gloves
  • Hammer
  • Masonry Trowels
  • Mortar Bag
  • Pail
  • Safety Glasses
  • Saw
  • Tape Measure
  • Wrecking Bar

Contact Us:

Looking for more glass block basement window installation tips? Give us a call or read our other articles about glass block windows. If you are searching for a professional glass replacement contractor to help you with your installation in Illinois: contact One Source Renovation, LLC at or give us a call at (815)-634-8922.