Historical Note
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Architectural Sealants Going about our daily business of inhabiting buildings, we should be blissfully unaware of the presence of sealants. Sealants fill in a building's gaps. These materials play a large role in making buildings weathertight but we seldom see them because they are hidden from view or, where visible, are purposely unobtrusive. Buildings protect their human occupants from the elements but must protect themselves, too. If water is allowed to penetrate into a building's structure, it can cause deterioration through rot, rust, or movement as it expands and contracts. Movement itself is inherent in buildings. We may think of buildings as stationary objects, but in fact they move around a good deal: Different materials within buildings expand and contract at different rates depending on changes in temperature and moisture, buildings settle on their foundations over time, wind pushes buildings around, and earth movements can toss them in all directions. A building's structure also moves because of the ways in which the building is used. A high-rise building may need to accommodate car traffic in a basement parking garage, high volumes of pedestrian traffic in a mall on its street level, moderate pedestrian traffic and equipment loads in offices on the next few floors up, and light traffic in apartments in the uppermost floors. Sealants help buildings deal with movement by allowing separate parts to move independently without losing weathertightness or allowing sound to pass where it is unwanted. Not all sealants perform all of the missions listed, but by definition they must maintain their integrity and shape while bridging some kind of gap. Elastomeric sealants are those which must be able to stretch, compress, and perhaps twist, yet return to their original form while accommodating movement. A sealanf s capacity to do this is usually expressed as a percentage of the width of the gap being bridged. The movement that elastomeric sealants used in buildings can withstand ranges from 12.5% to 50% or more. Non-elastomeric sealants, traditionally called caulking, are not expected to withstand much movement (2-7.5%). The middle range of movement capability is covered by, you guessed it, semi-elastomeric sealants. Sealants come in a variety of forms: flexible (elastomeric) gel-like polymers, gaskets, putties, tapes, and caulks. In
during this period with the development of elastomeric sealants. Rubber, which had already been used to manufacture gaskets, possessed many desirable properties: Synthetic rubbers and latex-based polymers were important starting points for further developments. Natural rubber was watertight and flexible under the right conditions, but was subject to cracking and deterioration in cold temperatures; it also had no adhesive properties of its own. Sealants based on polysulfide rubbers and polymers were the first elastomeric sealants to hit the market in the early 1950s. In 1960, thefirstindustry-wide standard stipulating the performance of polysulfide elastomeric sealants was developed. T
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