More than ever before major construction design and materials decisions have a decided sustainability element to them. Issues such as indoor air quality (IAQ), greenhouse gases (GHG’s) and energy independence have forced the issue into the spotlight. In making these decisions, we must remember that sustainability is inherently a balancing act between the social, the economic and the ecological. When making design choices, it is important to choose products not only for their ecological impact but their performance as well since premature replacement or worse can cause more overall ecological harm than good. Sealants, being among the best methods of saving energy as DOE has established when used properly, should be on the top of the list to be aware of when it comes to the right product for the job.
While many other technologies exist, there are essentially four basic technology types most commonly found in general commercial sealing today; acrylic-latex technology (acrylics), polyurethanes (PU), silicones and hybrid silicone-polyurethane technologies (hybrid). While validated third-party data comparing the LCA aspects of these technology types is not yet available, some assumptions can be made based on the production and technology generically. Following is those assumptions, as well as a general guide to choosing a sealant:
Silicones are inorganic and therefore do not deplete oil reserves. They are also low-VOC, though they do require significantly high temperature processes to create them. They have a very long service life in most cases (20 year warranties are commercially available) due to their inorganic base. They do tend to cost more than other technologies. They are the best sealant choice for glazing applications as many other technologies either have compatibility issues or performance issues in such a demanding situation. They are also ideal for kitchens/baths as they are inherently less likely to support microorganisms due to their inorganic nature. Being able to withstand higher temperatures, their use in hot areas such as HVAC is ideal as well.
PU sealants are now starting to be at least in part synthesized and include additives derived from materials based upon renewable resources, though they are still overwhelmingly petroleum-based. PU’s have shorter service lives (they are typically warranted for 5 years). Most formulations are very-low VOC, well below the current 4% by weight limit in some areas. This technology is the general purpose sealing technology used in commercial construction for both interior and exterior conditions such as traffic decks, around window frames, and even in continual immersion such as canals. Where they are not exposed to UV light, PU’s can last well beyond 5 years in most applications.
Acrylics are usually water-based and inherently low-VOC, but latex is shipped from once rain-forested areas globally, which is not GHG-friendly. Latexes tend to be less expensive, but depending on the application may not provide warrantees in commercial applications. They are not intended for exposure to adverse conditions where they will see significant moisture and temperature fluxes. They are paintable and compatible with most drywall compounds, though, and make excellent finishing sealants commercially.
Hybrid sealants have a PU backbone with silicone functionality, usually in the form of silyl terminations. They are inherently low-VOC, and have the same basic ecological pluses and minuses as PU sealants as they are well over 90% PU structurally. They do have the advantages of long service lives (up to 20 years is commercially warranted). Many are made overseas, having larger transport-related GHG associated as a result, though manufacturers are beginning to acquire the manufacturing technology in North America. Prices tend to be slightly higher than PU technology, but less than silicones generally speaking. These technologies are ideal for general exterior sealing and many interior applications as well.
As we see, every technology has ecological pluses and minuses. This is not just the case for sealants but air barriers, waterproofing, coatings and in essence all products across every major field. Each technology also has applications where they are the better choice more often than not. As such, anyone specifying products and technologies for a project like the sealants presented here, must consider the function as well as the ecological aspects in order to achieve truly sustainable design.
Michael Schmeida, MS, LEED™AP- Manager of Sustainable Programs at Tremco Commercial Sealants & Waterproofing