All face dimensions of hollow glass block are ¼ inch less then nominal size. In other words, 8 inch by 8 inch block is actually 7 ¾ inches square. Typically a ¼ inch mortar joint is used so that the center line of joint to the center line of joint is a full 8 inches or 6 inches or 12 inches depending on the nominal size of the block used.
What other physical properties do glass blocks have?
The insulation or R value of the Premiere Series (3 7/8 inch thick) glass block when installed with mortar is 1.96. The reciprocal U value is .51. The R value of our Thinline series (3 1/8 inch thick) glass block when installed with mortar is 1.75, the reciprocal U value is .57.
The visible light transmission of all hollow glass block products is 75% with the exception of ESSEX® AA pattern and LX filter blocks whose values range between 50 to 55%.
The STC, or Sound Transmission Class, of the Premiere Series glass block products range between STC values of 35 to 40 depending on the size of glass block. The STC value for the THICKSET® 60 Series block is 48, the STC value for the THICKSET® 90 Series block is 50, and the STC value for solid VISTABRIK® units is 53.
