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Building Pathology: restoration and durability of masonry construction; French: Restauration et durabilitÚ de mašonnerie; Romanian: Patologia cladirilor: reparatii si durabilitate pentru constructii de caramida

Pathology of building envelopes:
restoration and durability of masonry construction

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Summary
Early in the process of addressing the needs of contemporary masonry structures we have to face two problems:

  1. Model building codes (i.e. UBC, BOCA, NBC in Canada, etc.) have ballooned in size, price, and complexity. They are reissued every three years or so, making their producers more publishers of dubious material than problem solvers. The sponsoring organizations have become, more often than not, part of the problem, rather than the solution. In their futile attempt to include prescriptive "how to" language, their respective codes ended up becoming difficult and unwieldy.
  2. Masonry used to be an art and a science, yet after the second world war the art and pride that used to come with this craft diminished, and most masonry practitioners (architects, engineers, tradesmen) just do not have the time, inclination, and background to understand the underlying science.
  3. Budget restraints combined with technology that is moving too fast for the various training programs that prepare masonry craftsmen.
Masonry structures
Unfortunately, the life of masonry structures in North America is short and troubled. In my practice I see most masonry or stone veneers developing problems in 10-15 years of service. These problems become increasingly serious, generally before most buildings are less than 30 years old. At this point the rehabilitation needs of these existing buildings should be outpacing new construction. On the other hand, older, mostly load bearing masonry buildings, are getting to a point where more and more owners and developers decide in favor of retrofits rather than demolition. Retrofitting older buildings often involves upgrading the building shell so that both safety and environmental concerns (temperature and humidity) can be satisfied. However, especially in the case of older masonry buildings there are special problems due to the fact that they were not designed or built to operate within tight envelopes. The problems induced by these modified environments become acute at the high humidity levels required for the operation of modern construction. Unfortunately, general guidelines are difficult, if not impossible to develop. Many contemporary retrofitting methods will adversely affect the durability and the way these old masonry buildings behave. Recognizing this need for better approaches, owners should attempt to develop guidelines specific to their real estate portfolio. Erratic fixes, performed under duress after minor nuisances were allowed to become major problems, usually create rather than solve failures down the road. Ideally these guidelines should be independently developed, and include comprehensive checklists for the investigation, analysis, materials and construction process inspection, and long term monitoring of buildings. The most promising retrofit approaches for the particular type of building, loading and environmental conditions should be identified with a view towards the potential long-term behavior and impact on masonry walls.

Masonry cladding
Things become really complicated when we have to deal with the durability of masonry claddings; not only this depends on the masonry and building details, but also on the type, quality, and installation parameters of the anchorage system to the structure, as well as the back-up system itself. The problem in masonry claddings versus their load bearing counterparts is that they often have inadequate thermal mass and are prone to more movement. These induce additional stresses that cannot be handled effectively when new, much less after a few years of shrinkage, freeze-thaw cycles, and differential movement among others.



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