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Water Repellents for Concrete Masonry Walls

CMHA TEK 19-01

Water repellents are used on exterior walls to provide resistance to wind-driven rain. In addition, water repellents can also reduce the potential for efflorescence and staining from environmental pollutants, and enhance the color or texture of a wall.

When applied in accordance with manufacturer’s recommendations, water repellents effectively control water penetration. Water repellents are generally recommended for use on single wythe concrete masonry walls exposed to the weather. The choice of water repellent will depend on the surface to be protected, the exposure conditions, and on aesthetics. A wide variety of water repellents is available, offering many choices of color, surface texture, glossiness, and application procedures.

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Crack Control Strategies for Concrete Masonry Construction
Concrete masonry is a popular construction material because its inherent attributes satisfy the diverse needs of both interior walls and exterior envelopes over a wide array of applications. While these attributes are the primary basis for concrete masonry’s popularity, performance should not be taken for granted. Cracks in building assemblies and building materials may result from restrained movement originating within the material, as with volume changes due to moisture loss or gain, or from temperature expansion or contraction. Cracking may also be caused by movements of adjacent or supporting elements or systems, such as deflection of beams or settlement of foundations. In many cases, movement is inevitable and must be accommodated or controlled, which requires an understanding of the sources of stress that cause cracking. While would be a simple matter to prevent cracking if there were only one cause or variable, in reality crack mitigation requires identifying and addressing a combination of potential sources.This Tech Note reviews the common causes of cracking, from both internal and external sources, in concrete masonry construction and presents proven strategies and detailing approaches to mitigate and control shrinkage-induced cracks. The Solutions Summary section of this Tech Note provides a summary overview of these recommendations, with more detailed explanation, construction details, and background provided in the subsequent discussion.
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Concrete Masonry Highway Sound Barriers
This TEK covers acoustic requirements for concrete masonry highway sound barriers. For structural design considerations, the reader is referred to Allowable Stress Design of Pier and Panel Highway Sound Barrier Walls (refs. 3).
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Outdoor-Indoor Transmission Class of Concrete Masonry Walls
Providing a quality indoor acoustic environment is becoming a higher priority in many cases; particularly in urban environments where noise from traffic and other outside sources can be a significant distraction, especially in schools, homes and the workplace. Concrete masonry walls provide excellent noise control due to their ability to effectively block airborne sound transmission over a wide range of frequencies.
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Noise Control with Concrete Masonry
Sound control is an important design consideration in most buildings. Sound control involves two important properties: sound transmission and sound absorption, as depicted in Figure 1. The International Building Code (IBC, refs. 1, 2) contains minimum requirements for sound transmission in certain situations (see Sound Transmission Class Ratings of Concrete Masonry Walls, TEK 13-01D, ref. 3). However, the IBC does not contain minimum requirements for sound absorption, although proper control of sound reflected back into the room is a very important design function in many buildings as well, such as concert halls, gymnasiums, places of assembly, rooms containing loud equipment.
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Sound Transmission Class Ratings for Concrete Masonry Walls
Unwanted noise can be a major distraction, whether at school, work or home. Concrete masonry walls are often used for their ability to isolate and dissipate noise. Concrete masonry offers excellent noise control in two ways. First, it effectively blocks airborne sound transmission over a wide range of frequencies. Second, concrete masonry effectively absorbs noise, thereby diminishing noise intensity. Because of these abilities, concrete masonry has been used successfully in applications ranging from party walls to hotel separation walls, and even highway sound barriers.
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Concrete Masonry Unit Shapes, Sizes, Properties, and Specifications
The most widely used standards for specifying concrete masonry units in the United States are published by ASTM International. These ASTM standards contain minimum material and property requirements that assure quality performance. These requirements include items such permitted constituent materials, minimum compressive strength, maximum linear drying shrinkage, maximum absorption, permissible variations in dimensions, and finish and appearance criteria.The letter and first number of an ASTM designation is the fixed designation for that standard. For example, ASTM C90 (REF. 1) is the fixed designation for loadbearing concrete masonry units. The number immediately following indicates the year of last revision (i.e., ASTM C90-16 would be the version of C90 published in 2016). Because significant changes can be introduced into subsequent editions of standards, the edition referenced by the building code or by a project specification is an important consideration when determining specific product requirements. For the discussion presented here, the ASTM requirements reviewed have remained relatively static unless otherwise noted.
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Design for Dry Single-Wythe Concrete Masonry Walls
Single-wythe concrete masonry walls are cost competitive because they provide structural form as well as an attractive and durable architectural facade. However, because they do not have a continuous drainage cavity (as do cavity and veneered walls), they require special attention to moisture penetration.
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Joint Sealants for Concrete Masonry Walls
Successfully sealing joints, such as control joints and around door jambs and window frames, in concrete masonry walls depends on the overall design and construction of the entire building envelope. Movement joints (also called control joints) are needed in some concrete masonry walls to accommodate drying shrinkage, thermal movements, and movements between different building components. Movement joints, joints around fenestration, doors and penetrations, and isolation joints (joints at dissimilar material interfaces) rely on joint sealants to help preserve the overall weather-tightness of the building envelope. In addition, properly sealed joints may be required to meet a specified fire resistance rating or sound transmission class.
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Flashing Details for Concrete Masonry Walls
At critical locations throughout a building, moisture that manages to penetrate a wall is collected and diverted to the outside by means of flashing. The type of flashing and its installation may vary depending upon exposure conditions, opening types, locations and wall types. This TEK includes typical flashing details that have proven effective over a wide geographical range. The reader is also encouraged to review the companion TEK 19-04A Flashing Strategies for Concrete Masonry Walls (ref. 1) which addresses the effect of moisture on masonry, design considerations, flashing materials, construction practices, and maintenance of flashing.
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