In today's commercial construction and renovation markets, the building owner desires a structure that remains both free of leaks and aesthetically pleasing for many years. It is assumed by many designers that within the group of high performance sealants “a silicone is a silicone”, indicating that a sealant in a generic class carries with it both the positive and negative characteristics associated with that class. Silicone is generally considered the premium performing material, exhibiting excellent durability. However, occasional appearance problems, generically assigned to silicones, have swayed some specifiers away from silicones on some substrates. The contributors to appearance problems are many, and only a few are specifically related to the sealant used.
This paper describes several sealant related phenomena which can contribute to building aesthetic problems. These include sealant dirt pick-up, substrate staining and fluid migration into porous substrates. Each of these terms is defined in detail. Laboratory and weathering tests are described which indicate how quickly and how severely aesthetic problems develop. Results are reported for sealants representative of the following types: plasticized silicones, unplasticized silicones, unplasticized surface-modified silicones, plasticized polyurethanes, unplasticized polyurethanes and plasticized modified polyethers. The influences of local environment, joint design and application technique are also discussed.