Change of Color
This term is self-explanatory, however, there are several mechanisms, which can cause changes in color. First, there are mechanisms that are inherent in the sealant. For example, a change in color can be caused by the insufficient color fastness of one of the pigments used in the sealant formulation. A darkening of a sealant may be simply the first stages of dirt pick-up or microbial growth, as the whitening of the sealant may be the first stages of chalking. Second, there are a number of mechanisms that are induced by factors external to the sealant. Probably the most important example of these is the incompatibility with other building materials, such as backing materials, building substrates, or the remnants of a failed building sealant in a resealed joint. Incompatible materials then migrate from the other building material into the sealant and cause it to change color. Examples of such incompatible materials are low molecular weight polymers, plasticizers, antioxidants, bitumen, or tar.
FIG. 1—Atlas VIEEWm digital image analyzer.