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Jason Thompson

Grouting 4 in. CMU

Question

I'm often asked if it feasible to grout 4 inch (100 mm) concrete masonry units. To which I reply "No"...or possibly "Good Luck". While there is no code prohibition on grouting hollow 4 inch CMU, the size of the cells makes doing so pretty impractical - especially if reinforcement is present.

The primary reason is illustrated in the accompanying photos showing a 4 inch CMU from the top of the unit (as made) and the same unit from the bottom (as made). While the width of the cells at the top of the unit could lead one to believe grouting is possible, due to the tamper of the cells opening width transitions from about 1.5 inches to around 0.75 inches. 

Is it impossible to fill these hollow 4 inch units with grout - no. But if a solid 4 inch unit is needed for whatever reason(s), it's easier, faster, and less expensive to simply specify a solid 4 inch unit.

4 in. Block Top (As Made).jpg

4 in.  Block Bottom (As Made).jpg

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