I am getting these glass block spacers for 4" blocks but the website I got it from says nothing about the thickness of the joint it provides.

enter image description here

I would like to build my framing before it arrives (could be up to 2 weeks) in the meantime but, for that, I need to factor the joint to calculate the width my glass block window. Can you guess it from the picure (my guess is something like 3/16-1/4")?


This site says 4” modules in both directions. (I know some glass blocks come in 6” modules.)


So to answer your question, the mortar joint is going to be as wide as necessary to provide a 4” module. (The spacer will make the joint the correct width.)

Don’t forget to add one mortar joint width for your wood frame

  • To clarify, the answer is 4" minus the actual dimension of your particular blocks. The thickness of the spacer arms is not related to the final mortar joint thickness.
    – isherwood
    Jan 24 '19 at 20:39

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