Masonry Magazine March 1982 Page. 1
masonry
MARCH 1982
This publication is prepared by the staff of the Portland Cement Association. It is intended for use by qualified professional personnel who are competent to evaluate the significance and limitations of its contents and who will accept responsibility for the application of this material. The Portland Cement Association disclaims any and all responsibility for application of the stated principles or for the accuracy of any of the sources other than work performed or information developed directly by the Association.
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**Keywords:** brick, concrete block, construction, control joints, cracking, design, economics, masonry, mortars, reinforcement, specifications.
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**Abstract:** This issue discusses the causes of cracking in masonry walls and recommends design and construction practices to minimize cracking. Topics include: movement joints, mortar selection, reinforcement, and construction practices.
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**Cracking in Masonry Walls**
Cracking is probably the most common complaint voiced by owners of masonry buildings. Cracks are unsightly and may give the impression of poor workmanship or structural distress. Cracks can be caused by a variety of factors, including:
* Volume changes due to moisture or temperature
* Differential settlement
* Applied loads
* Seismic forces
Although it is virtually impossible to build a masonry wall that is completely crack-free, the size and number of cracks can be minimized by following good design and construction practices.
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**Movement Joints**
Movement joints are designed to relieve stresses caused by volume changes in masonry walls. They should be located at points of weakness in the wall, such as:
* Changes in wall height or thickness
* Corners
* Intersections of walls
* Near large openings
The spacing of movement joints will depend on the type of masonry, the climate, and the amount of reinforcement in the wall. As a general rule, movement joints should be spaced no more than 20 feet apart in unreinforced masonry walls and no more than 40 feet apart in reinforced masonry walls.
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**Mortar Selection**
The type of mortar used in a masonry wall can have a significant impact on its resistance to cracking. Mortars with high compressive strength tend to be more brittle and more prone to cracking than mortars with lower compressive strength. For this reason, it is generally recommended that a relatively low-strength mortar be used for masonry walls. Type N mortar is a good choice for most applications.
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**Reinforcement**
Reinforcement can be used to control cracking in masonry walls. Horizontal reinforcement is particularly effective in resisting tensile stresses caused by volume changes. Vertical reinforcement can be used to resist bending stresses caused by wind or seismic loads.
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**Construction Practices**
Good construction practices are essential for minimizing cracking in masonry walls. Some important considerations include:
* Using proper mortar mixing and application techniques
* Protecting masonry from moisture during construction
* Allowing masonry to dry properly before applying finishes
* Avoiding excessive loads on masonry walls during construction
By following these recommendations, it is possible to build masonry walls that are both durable and aesthetically pleasing.