Water insensitive bonded perlite structural materials

An improved water insensitive structural material consisting essentially of reactive expanded perlite bonded by an in situ produced water insoluble, crystalline reaction product of said expanded perlite and at least one alkali metal silicate selected from sodium silicate and potassium silicate, said structural material being made by a process comprising the steps of:

• (a) mixing from about 1 to about 2 parts by weight of a filler material having at least 75 parts by weight reactive expanded perlite with about 4 to about 1 parts by weight of an aqueous solution of said at least one alkali metal silicate and when said alkali metal silicate is sodium silicate, the weight ratio of SiO.sub.2 to Na.sub.2 O is from about 3:1 to about 4:1 and the solids content is from about 28 to about 34 weight percent and when said alkali metal silicate is potassium silicate, the weight ratio of SiO.sub.2 to K.sub.2 O is from about 2:1 to about 2.6:1 and the solids content is from about 24 to about 30 weight percent;
• (b) thereafter compressing the mixture from step (a) into a coherent article;
• and
• (c) thereafter subjecting the coherent article from step (b) to a one-stage curing process in which the article is maintained through the entire curing process at a temperature about 180.degree. F. to about 225.degree. F. at a relative humidity of from about 30% to 60%.