The Burkard family, Winkler’s fourth-generation offspring and Sika’s biggest shareholder, agreed to sell its 16.1 percent stake and control of the voting rights to Cie. de Saint-Gobain SA. The move caught both the management and investors off guard, with the stock sliding the most on record. Sika’s chief executive officer went into open rebellion and threatened to quit, while his counterpart at France’s Saint-Gobain sought to defuse the situation, saying they had been approached.