While there are three basic types of sealants in general use today- mastics, thermoplastics, and elastomers- there are also many variations of materials which fall under these classifications. Each product has its place. For example, elastomers have been used in building structures; thermoplastices in highway construction; and mastics and thermoplastics in concrete floors. The term mastic embraces that group of sealants which are formulated form viscous liquids such as non-drying oils or low melting point asphalts. Fillers such as asbestos fibers or siliceous material are added to these liquids. Mastics are useful in reservoirs and sewage plants were the temperature range is comparatively small and where they are not subject to attack by chemicals stronger then chlorinated water or treated sewage. Additionally, under there conditions, the mastic is protected form the destructive effect of ultraviolet light rays. Mastics require some type of installation equipment. A regular, hot melt asphalt sealant is melted directly in an asphalt melting pot similar to those used by roofers, and pumped or poured directly into the joint. Cold applied, ready to use mastic sealants are usually pumped directly form the pail or drum medium, but the air is not midxed with the material. September's issue discusses thermoplastic sealants.