Q: We are designing a building using 4x8x16 polished CMU anchored veneer. In addition to the anchors, do we need to include joint reinforcement?
-Joint reinforcement In Masonry
Dear JIM:
YES! Concrete Masonry anchored veneers follow similar recommendations for crack control that structural CMU walls do. Movement caused by temperature changes, moisture-volume changes, de lection and/or shrinkage needs to be accommodated. Shrinkage cracks in concrete masonry aren’t a structural concern but an aesthetic one, though they could potentially provide a pathway for water. Crack control measures include 2 components: horizontal joint reinforcement and control joints. The “rule of thumb” or empirical method is to have horizontal joint reinforcement every 16” oc with control joints placed at a maximum panel length to height ratio of 1 ½. For example, a 10’ tall wall would need a control joint every 15’. The maximum spacing no matter the height would be 20′ for veneers and 25′ for structural walls. Control joints would also need to be placed where stress concentrations occur (such as openings and corners). Want to have fewer control joints? Crack control is a ratio between control joint spacing and the amount of horizontal steel reinforcement in the wall (joint reinforcement for veneers and/or rebar for structural masonry). It is possible to have control joints further apart if there is more steel in the wall using the “alternative engineered method” outlined in NCMA TEK 10-3. We see this out in California where there is a substantial amount of horizontal reinforcement due to seismic concerns. There, control joints are usually eliminated altogether. For more, see TEK 10-4, Crack Control for Concrete Brick and Other Concrete Masonry Veneers.
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Heidi Jandris is a technical expert and trusted voice of the industry. She part of the family business’s 3rd generation, grew up immersed in all things concrete block and worked as a welder at the plant before getting her BArch at Pratt Institute in Brooklyn NY. She is the Sustainability Manager and provides technical and design services for A. Jandris & Sons.
