I’ve been check your site in there and i make an example page for you here http://robinoude.fr/wp-admin/post.php?post=174&action=edit . You can also check the attached image url below, it’s just works fine https://www.dropbox.com/s/xti434spi31yofj/Screenshot%202016-06-23%2010.23.30.png?dl=0
Unfortunately, at the moment we don’t Visual Composer option for every page template. It only be available on Landing Page (Landing Page Builder – Page Template) and Portfolio Landing Page type (Portfolio Item with Extended Layout).
Let us know if you have further question.