The thermoplastics are those materials such as rubber asphalts, pitch, coal tar and jet-fuel resistant materials which become plastic when heated. These products are primarily used in the highway, airport and street paving field. With few exceptions, the thermoplastics must be treated before they are poured into the joint slot. In most cases, the temperature to which they should be heated is critical and for this reason a double boiler type melting machine is required. One of the most recent developments in the thermoplastic field is a product which really falls somewhere between the thermoplastics and the elastomers. This sealant is make in two grades. One is used in non-critical areas such as highways and runways and the other is used in areas such as warm up aprons and taxiways where jet-fuel spillage of jetblast is involved. This material has many advantages over most thermoplastics in that is manufactured and delivered as a liquid. Most of the others are solids which have to be melted down. This particular product still has to be heated but since it starts out as a liquid it can be heated quite rapidly. There are a few rubber asphalt type materials on the market which do not require heating before being used. Some of these are two part material and others are single component materials ready for use. Logically, cold poured seals on should not be included under the heading of thermoplastics since the term "thermoplastic" indicates a softening under heat and the ability of be melted a number of times without adverse effect. In addition to the thermoplastics and the cold poured or cold-applied materials, there are also the so-called butyl rubbers. These are no-skinning sealants made from poly-isobutylene and poly-isobutlysene. They are compounded with resins, oils, fillers, sovents, and pigments to produce a wide range of sealing compounds. The butyl rubbers are nonoxidizing and almost non-curing since they remain tacky for an extremely long period of time. In this respect, they resemble the non-hardening mastics. These sealants are used more as caulking compounds than as joint sealers