Question:

• What is flexible sealant ? Why must we use sound tested flexible sealant for sound rating drywall partition and ceiling systems, and fire tested flexible sealant for fire rating drywall partition and ceiling systems ?

   

Answer:

• Flexible sealants are polymerized products, used for caulking peripheral gaps between walls and floors, walls and ceilings, newly built and existing walls, door/window frames encompassed by walls, pipe penetrations through walls and ceilings, etc. Flexible sealants are thick paste when packed in cartridges / sausages / tubs, will gradually dry out when exposed to air, but remain their permanent elasticity when completely dry. They can be made from a variety of chemical susbtances and thus, can be either acrylic based, silicone based, or polyurethane based, copolymer based, etc. 
  

   

• Regardless of their chemical origins, most flexible sealants can be used to caulk gaps to ensure the sound insulation rating for wall and ceiling systems as designed. However, it should be noted that while strongly adhere to acrylic and polyurethane sealants, water based paints are hard to stick to gaps filled with silicone sealants. As a result, silicone based sealants should not be used for gypsum / masonry walls and ceilings that need to be finished with water based paints.
  

   

• In general, a good designed sound rating drywall partition system has a minimum laboratory sound reduction index Rw = 50 dB(A). This rating might be achieved if all gaps are carefully caulked with sound tested sealants during the installation phase. Any built up system in situ having gaps unsealed with flexible sealants, on purpose or by chance, would have a field sound insulation rating R'w much lower than its designed level; in some cases, the sound insulation performance of said system might be downgraded to 30% of its original design.
  

   

• For wall and ceiling systems specially designed to have a certain fire rating level, all gaps must be caulked with fire tested sealants to the full depths and widths specified in relevant drawings. If gaps are only filled with normal sealants which are sound tested but not fire resistant, when in fire, the flame will rapidly break through the sealed gaps and spread from one area to the other. Most so-called "Fire Rating" gypsum / calcium silicate drywall partition and ceiling systems already built up in Vietnam , including but not limited to modern offices and cinema complexes located at splendid commercial building projects, whose fire resistance is of vital importance, by intention or by chance, do not have this indispensable component in the installed systems.