Abstract: A retarding heat tracing system amd method of making same adapted to externally heat a process pipe including a channel member, a heat transfer element, a retarding heat transfer strip made from a retarding heat transfer material, and a plurality of clamping members. The retarding heat transfer strip has a longitudinal cavity which receives the heat transfer element. The external shape of the retarding heat transfer strip substantially conforms to a longitudinal recess of the channel member. The retarding heat transfer strip with heat transfer element is positioned in the recess of the channel member and the clamping members attach the channel member to the process pipe. The retarding heat transfer material optimizes the heat transfer between the heat transfer element and the process pipe while minimizing the heat transfer element heat loss.

Abstract: Improved water insensitive bonded perlite structural materials are produced by combining expanded perlite with an aqueous solution of an alkali metal silicate and thereafter molding the mixture into a desired shape and curing the molded mixture under closely controlled temperature and humidity conditions. The aqueous solution of alkali metal silicate will be either a sodium silicate solution or a potassium silicate solution. The temperature and humidity conditions for curing the molded perlite and alkali metal silicate mixture are from about 180.degree. F. to about 225.degree. F. and from about 30% to about 60% relative humidity. By carrying out the curing process under the closely controlled temperature and relative humidity conditions, a water insoluble crystalline reaction product is formed between the alkali metal silicate and the reactive expanded perlite.