Copper Piping Systems and Acoustical Sealants

There are many situations in the built environment in which copper piping systems, as well as other piping, electrical, HVAC and necessary building services systems penetrate non-fire rated floors, ceilings and partitions. Depending on the size and complexity of the building, these penetrations can number in the tens of thousands.

In many instances, it is desirable to completely seal these penetrations in non-fire rated partitions to prevent the spread of smoke in case of a fire, or to attenuate the transmission of sound from one building area to another during normal building operation.

There are a number of products on the market designed specifically for this purpose, to provide a non-fire rated acoustical or smoke spread seal between the piping, electrical, or other system and the surface through which they pass, most commonly a drywall surface. Among these are acrylic, acrylonitrile, and other latex based sealants/caulks, silicone-based sealants/caulks, and others.

There are also a variety of penetration details that a designer or installer can employ when making the penetration, such as using a sleeved penetration (vented or unvented, using various sleeve materials) or an un-sleeved penetration.

In evaluating all of these possibilities for sealing copper piping systems passing through non-fire rated partitions the designer and installer should consider the following:

  • In both sleeved and un-sleeved penetrations the interstitial or annular space between the exterior of the copper piping system and the partition surface or interior surface of the sleeve should be as small as possible (less than a ¼" gap is preferred). Acoustical/Smoke-stop sealants should only be applied in a small bead between the piping system and the penetration; excessive gaps between the two require excessive amounts of sealant and longer cure times. Cure times are further impacted under adverse environmental conditions, thus exposing the copper surface to compounds in a wet condition that can etch or cause minor surface corrosion and discoloration on the copper surface.
  • In both sleeved and un-sleeved penetrations where the interstitial space between the exterior of the copper piping system and the partition surface or interior sleeve is excessive (greater than ¼" gap) the interstitial space shall be filled with an appropriate backer (mineral wool for example) prior to application of the acoustical/smoke-stop sealant to prevent the introduction of excessive amounts of sealant into the interstitial space. Situations have been reported where the use of acrylic latex and acrylonitrile latex-based acoustical sealants such as USG Sheetrock® Brand Acoustical Sealant and Hilti® CP 506 Smoke and Acoustical Sealant have been used to seal unvented, sleeved penetrations and un-sleeved penetrations with excessive gaps between the exterior of the copper piping system and the penetration. In these cases, compounds within the wet sealant (likely formates and acetates) combined with longer cure times due to the excessive amount of sealant have combined to cause discoloration and general minor surface corrosion of the copper piping. While detailed examination of these occurrences indicate that the surface corrosion is nothing more than an aesthetic concern, and has not resulted in aggressive corrosion attack or premature failure of the copper piping, this is still an undesirable situation that should be avoided where possible.
  • Where strict control of the size of the interstitial/annular space cannot be ensured, or a backer material is not used, designers and installers should work with the acoustical/smoke-stop sealant supplier to ensure that sealants do not contain compounds (formates, acetates, sulfur, and ammonia compounds are most commonly of issue in sealants) that may cause corrosion of the copper piping system. Many silicone-based sealants/caulks have shown good service in this regard.

Designers, installers, inspectors and building owners should remember that discoloration of the copper surface does not necessarily indicate a cause for concern, as slight surface discoloration is a typical reaction between copper and many compounds, especially when they are in a wet state. Copper has long been used successfully because of its outstanding corrosion resistance to atmospheric, process and building compounds. Its success is primarily due to its ready ability to react with such compounds to form a protective surface scale or patina, most usually notable by an even, general discoloration and surface corrosion film across the copper surface. In the absence of discrete deep pitting this is not generally an indication of aggressive corrosive action.

Engineers, installers, inspectors and building owners should be cognizant of the above recommendations and require that appropriate penetration details and materials are used to ensure the lifetime of service delivered by the copper piping system.