F08-CMU-Troubleshooting Guide
Common Problems
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Common Solutions
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Pop-out CMUs
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Free lime may be present, which when hydrated creates calcium hydroxide, which in turn causes a volume increase. Exposure to the air (and carbon dioxide) forms calcium carbonate, which results in the white streaks on the sides of buildings (efflorescence). It would be worthwhile to send samples of the building material to get tested for free lime and test its properties so that one could tell how long they have before the bricks need to be replaced. |
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How much joint reinforcement is needed?
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Joint reinforcements are needed (along with control joints) in exposed concrete masonry walls to control cracking associated with drying shrinkage. The National Concrete Masonry Association (NCMA) has a long list of recommendations regarding CMU construction, and in this case one such bit of information is that the distance between control joints not exceed the lessor of 1.5 times the height of the wall or 25 feet. Read up more of what the NCMA has to say. It is important to note that control joints are used much more liberally on buildings that have an aesthetic requirement.
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Is it better to fully bed concrete masonry units rather than merely face-shell bedding them?
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Cross webs with mortar do not significantly increase the strength of a concrete masonry wall. Most of the durable strength of the concrete masonry is provided by the mortar in the exterior portion of the wall on the interior and exterior faces. It takes much more time and effort to fill cross webs with mortar, and for this reason cross webs are only filled when the cells are to be grouted. In most reinforced masonry walls, that's only a small portion. Cross webs must be filled to prevent grout from flowing out to adjacent cores that will not be grouted. It really depends on if the plans call for this (or face-shell bedding), because then all of the above and more have been taken into consideration.
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How much bracing is enough? |
As with every project this varies, and by far the most important answer to this question can be given by your local structural engineer, so ask him! Studies have shown that simple reinforcing rods driven into the ground do not provide adequate support in a majority of cases. Two 2 x 4 members driven at least a foot into the ground provide better support, but even these are not usually sufficient for any safety regulations. The best bracing is all proportional to the size of the wall your building, one that is strong, can survive soil changes, and will not slip or break under tension. Again the best answer is to ask your structural engineer. |
Sources and additional information:
http://findarticles.com/p/articles/mi_m0NTA/is_/ai_n6090141
http://www.ncma.org/Pages/default.aspx
http://findarticles.com/p/articles/mi_m0NTA/is_/ai_99697480
Picture Links:
http://farm3.static.flickr.com/2010/2338258383_b4501c0612_o.jpg
http://www.masonrymagazine.com/12-02/art/joints-Figure-1.jpg
http://www.simpsonanchors.com/images/catalog/large/073a-2008.gif
http://www.masoncontractors.org/codesandstandards/wallbracingfaq/images/wallbracingfaq-1.jpg |
