Fracsal crosslinking additives consist of a specifically sized, sparingly-soluble borate crosslinking agent, suspended in either a low aromatic content carrier fluid or an aqueous solution, which is capable of adjusting the rate at which gelation of guar or derivatized guar occurs in a water-based fracturing fluid. Fracsal concentrates are typically added as a continuous mix during pumping operations to produce a unique gel that is elastic, thermally stable, and has the ability to re-form a stable structure after shearing.