The aging of a novolak resin solution used in iron-making blast furnace taphole clays is reported. The novolak resin propylene glycol solution was aged at temperatures between 2 and 80degreesC for up to 56 days. The viscosity was measured to evaluate the change in the resin's behavior. A cure reaction was found to occur with the addition of hexamethylenetetramine (HMTA) at temperatures lower than had previously been reported. Methods for handling and storage of taphole clay to avoid excessive increases in viscosity due to aging are discussed. An approach for estimating the long term aging at temperatures of 30 to 50degreesC was considered using shorter term aging data obtained at 70 and 80degreesC. (C) 2004 Wiley Periodicals, Inc.