Abstract: A method of building viscosity in a sheet molding composition is provided that includes a thickening agent of at least one of magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxides, zinc oxide, borates, aluminum ion chelates, aluminum trihydrate, polyphosphate, epoxides being mixed into a phenolic resin liquid or solution that includes novolac resin. An initial viscosity results for the mixture. The viscosity builds from the initial viscosity to 36 hours, from 36 to 142 hours, and then from 142 hours to 176 hours to define a slope ratio of viscosities in these time ranges of 1.5-8:1:-0.4-2 and a having terminal viscosity as measured at 176 hours. Alternatively, the initial viscosity is between 500 and 50,000 centiPoise (cP) and at 24 hours thereafter builds to between 1 million to 50 million cP, and the terminal viscosity thereafter of between 10 million and 200 million cP.