Acoustic block in Reinforced Walls

Acoustic blocks and similar products have a long history of being used in various applications to absorb sound. The purpose of this page is to provide insight on how to incorporate acoustic block while considering potential issues that come with using these types of units in a masonry wall system.

This page is part of a larger series of specification examples meant to highlight cases where vague or poorly written items have lead to issues on masonry jobs across Canada.


The information contained here is intended to serve as educational content for designers, specifiers, or contractors. It is not to be relied upon for formal technical advice, as masonry projects may have details and considerations that are unique to a particular project and may be beyond the scope of the content of this page.

If there are any questions or concerns regarding masonry design or construction, CMDC offers technical assistance to our supporting members, as well as the design community.

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How the original specification typically appears:

X.Y.     Acoustical block:

X.Y.a   to CSA A165 Series, Type H/15/C/M in metric modular size. Exposed faces of uniform texture with reverse funnel shaped slots (two per block) and having black glass fibre filled cavities. Minimum NRC to be 0.65; 300 mm nominal size unless indicated otherwise “XXXX Block” Type XXXX manufactured by XXXX or other approved product.

X.Z      Placing of Block and Brick Units  

X.Z.a   Lay the work from face side to line and level. Accurately space courses. Keep the bond plumb throughout. Install corners and reveals plumb and true. Form uniform size joints. Check work regularly.

X.Z.b   Lay interior block walls in running bond.

How the original structural note typically appears:

X.Y      Reinforced Masonry

X.Y.a Unless otherwise noted, reinforce loadbearing 190 masonry with 15M@1200 vertical + 2-4.8 diameter wire ladder-type horizontal reinforcing at 400 centres. All other masonry is non-load bearing, refer to architectural specifications for reinforcing requirements.

X.Z      Grouted Masonry

X.Z.a Unless masonry walls are noted as “Fully-grouted” or “Grouted solid”, grout only cells containing vertical or horizontal reinforcement and anchor rods or straps, and other areas specifically indicated on drawings.

Discussion points to consider when specifying masonry with acoustic units:

Some geometries of Acoustical/Sound Block units allow for placement of vertical reinforcement; however, those configurations may differ from that of a standard stretcher concrete block unit (with 3 webs and two cells). Some geometries of Acoustical/Sound Block units do not have the centre web and therefore have only one cell for the placement of reinforcement. Webs of units are one means by which sound is conducted through a material, reducing the web area and specially designing the configuration of these units is how they achieve their desired acoustic effect in the field.

The cells in a standard stretcher concrete masonry unit align in a way that allows grout to flow down to the base of the wall and surround the reinforcement within the cell. The webs in the unit form a barrier preventing the grout from seeping into adjacent cells that are not to be grouted, in cases of partially-grouted masonry. Typically there is sufficient overlap of webs in these units that the mason can use mortar to help contain the grout. For certain types of Acoustical/Sound Block units that have a single cell, it is not possible to align the webs to permit partially-grouted masonry. A possible work around to this would be to construct the wall in a stack pattern fashion (i.e. no over lap of units between adjacent courses). This would ensure that each cell in each unit is vertically aligned and then partial-grouting of the wall can be completed, however, stack pattern walls require additional design considerations over running bond.

The above specifications and structural notes pose a conflict for cases where wall containing Acoustical/Sound Block must be reinforced and partially-grouted. Stack pattern walls have very specific design requirements and cannot be treated as structurally equivalent to a wall constructed in running bond. Similarly, partially-grouted masonry cannot be treated as structurally equivalent to fully-grouted masonry. In this case there is an inherent conflict for the installer that may only be resolved from the design team side.

Finally, it is important that the most recent editions of relevant CSA standards are referenced. In the case of uncertainty, one can find out the relevant edition of the standard in the list of referenced documents accompanying the building code in effect for you specific area.

Suggested Changes to the Specification:

It is not possible to provide specific recommendations to the language of the specifications without conducting a complete design analysis. In this case it would be pertinent for the design team to recognize this conflict and resolve it since both options (constructing the wall as fully-grouted in running bond or partially-grouted  in stack pattern) have structural design implications.

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