golf39
Structural
- Mar 1, 2007
- 13
I review Structural Drawings on numerous Commercial Buildings across the U.S.A. If properly designed there is no better wall system than a double wythe masonry wall with CMU backup and Brick Veneer. I do not understand how most architects appear to be driving the train when masonry construction is concerned and I have seen the following, which does not seem to be good engineering practice to me. I would appreciate hearing other professional opinions.
1. Single Wythe CMU walls, are shown with no dry block additive required for CMU or mortar. Featherlite in SW area uses dry block additve in their block, but other manufacturer's may not unless specifically required to do so by the specifications. The masonry contractor likewise will not use dry block additive unless it is contained in the specifications. CMU is like a hard sponge and will collect water and efflourensence will occur, unless dry block is used to help inhibit it. Silane and Siloxane water repellent coatings and paint coatings may help over the short term, but have to be periodically reapplied to provide continual protection. While this can occur in brick it is far less of a problem than CMU. There is no way to properly drain or flash a single wythe masonry wall, but architects seem to continue to require them. It is my professional opinion single wythe CMU walls should not be used except for austere facilities such as remote pump houses etc. where interior finishes are not required as they are prone to leakage.
2. Brick or CMU Veneer with Steel-Stud Backup while less of a problem than single wythe walls are used extensively by architests. However, they often do not follow Brick Industry recommendations. See Tech Notes 28B Brick Veneer/Steel Stud Walls by Brick Industry Association. Several Mansory Associations have shown that this type construction is the same or less expensive than Brick Veneer with CMU Backup. Thereore, I do not see any advantages as the veneer will crack more with a less rigid backup and the additional weight on the foundation is usually slight. Also I am seeing more CMU veneers being used. However; horizontal joint reinforcement is often neglected and should be provided for shrinckage & crack control. Yes, brick expansion joints have to be provided in the brick veneer also, but brick is a superior veneer to CMU due the problem outlined above.
3. I have seen grouted & ungrouted CMU stem walls on top of spread footing instead of using concrete stem walls below grade for commecial construction. It is my opinion masonry should not be installed below grade without being waterproofed. Brick Industry Association seems to agree. See Tech Notes 28B,noted above, but CMU manufacture's seem to show CMU being used below grade withouit being waterproofed. Therefore, if you have to waterproof masonry below grade, why would't you use concrete. I am not talking about basements, where waterproofing of the concrete would still be required.
4. CMU & Brick being placed at grade with no masonry/brick ledges. Therefore, the foundation and first joint of Masonry cracks allowing water penetration in driving rain. (Have investigated this on numerous existing building, but I still see it frequently on Commercial Buildings Drawings).
While I have not covered all wall systems, these appear the most commonly used in masonry construction and using masonry at or below grade should be avoided as outlined above. Your comments would be appreciated.
1. Single Wythe CMU walls, are shown with no dry block additive required for CMU or mortar. Featherlite in SW area uses dry block additve in their block, but other manufacturer's may not unless specifically required to do so by the specifications. The masonry contractor likewise will not use dry block additive unless it is contained in the specifications. CMU is like a hard sponge and will collect water and efflourensence will occur, unless dry block is used to help inhibit it. Silane and Siloxane water repellent coatings and paint coatings may help over the short term, but have to be periodically reapplied to provide continual protection. While this can occur in brick it is far less of a problem than CMU. There is no way to properly drain or flash a single wythe masonry wall, but architects seem to continue to require them. It is my professional opinion single wythe CMU walls should not be used except for austere facilities such as remote pump houses etc. where interior finishes are not required as they are prone to leakage.
2. Brick or CMU Veneer with Steel-Stud Backup while less of a problem than single wythe walls are used extensively by architests. However, they often do not follow Brick Industry recommendations. See Tech Notes 28B Brick Veneer/Steel Stud Walls by Brick Industry Association. Several Mansory Associations have shown that this type construction is the same or less expensive than Brick Veneer with CMU Backup. Thereore, I do not see any advantages as the veneer will crack more with a less rigid backup and the additional weight on the foundation is usually slight. Also I am seeing more CMU veneers being used. However; horizontal joint reinforcement is often neglected and should be provided for shrinckage & crack control. Yes, brick expansion joints have to be provided in the brick veneer also, but brick is a superior veneer to CMU due the problem outlined above.
3. I have seen grouted & ungrouted CMU stem walls on top of spread footing instead of using concrete stem walls below grade for commecial construction. It is my opinion masonry should not be installed below grade without being waterproofed. Brick Industry Association seems to agree. See Tech Notes 28B,noted above, but CMU manufacture's seem to show CMU being used below grade withouit being waterproofed. Therefore, if you have to waterproof masonry below grade, why would't you use concrete. I am not talking about basements, where waterproofing of the concrete would still be required.
4. CMU & Brick being placed at grade with no masonry/brick ledges. Therefore, the foundation and first joint of Masonry cracks allowing water penetration in driving rain. (Have investigated this on numerous existing building, but I still see it frequently on Commercial Buildings Drawings).
While I have not covered all wall systems, these appear the most commonly used in masonry construction and using masonry at or below grade should be avoided as outlined above. Your comments would be appreciated.
