Saint-Gobain Chief Executive Pierre-Andre de Chalendar said its purchase of 52.4 percent of the Sika voting rights from the Burkard-Schenker family was "absolutely irrevocable", and the deal would close in the second half of 2015 at the latest.
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The Saint-Gobain chief said he was surprised by Sika's reaction, saying the French firm had held constructive discussions on Saturday and planned to retain Sika's management team after the takeover.
Sika's Chairman Paul Johann Haelg made it clear at a news conference in Zurich on Monday that the company's executives were not on board: "This transaction is not in the interest of Sika and its public shareholders."
Sika said in a statement that all non-family board members and the entire company's management will resign when and if the transaction goes through.
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A problem for Sika shareholders is that the Burkard-Schenker family's majority voting rights come with only 16.1 percent of the shares. Saint-Gobain, however, will be able to incorporate Sika onto its accounts without buying any of the other 85.9 percent of the shares.
"This is a disaster for the public shareholders, among them pension funds," said Gregor Greber, chairman of Zurich-based shareholder advisory group ZRating.
Saint-Gobain, Europe's biggest supplier of building materials, said it hoped the deal would generate 100 million euros ($120 million) in annual cost savings from 2017, 180 million from 2019, and create value by the fourth year.
Sika, the world's leading supplier of construction chemicals, said it could not see the industrial logic for the deal and disputed Saint-Gobain's cost savings estimates.
To stay independent, Sika would have to find a "white knight" bidder to top Saint-Gobain's offer to the Burkard-Schenker family, said Bank Vontobel analyst Christian Arnold.