Holcim shares will be swapped at the rate of 0.9 Holcim share for one Lafarge share.
Filaret Galtchev, a Russian billionaire who owns 10.8% of Holcim, is also said to be still opposed to the merger.
The capital increase of Holcim that will be used to support the merger will be submitted to a shareholder vote on 8 May 2015. Holcim needs the approval of 66% of shareholders.