BERLIN, Oct 19 (Reuters) - Activist investor Petrus Advisers on Wednesday criticised a 25 euro per share offer for German roof tile maker Braas Monier from U.S. rival Standard Industries as too low in an open letter to Standard Industries owner 40 North.
* "40 North's offer is a mistake," London-based Petrus writes in a letter to 40 North, published on its website.
* Standard Industries' offer for Braas Monier values it at about 1.9 billion euros ($2.1 billion) including debt. The German company has rejected the offer as too low.
* The Petrus letter says that "25 euros per share substantially undervalues Braas Monier even before taking into account the synergies 40 North wants to reap".
* Petrus holds a little less than 3 percent of Braas Monier, a source close to the matter said. It would have to declare its stake only when it passes the 3 percent threshhold.
* Petrus said it will not tender its shares at 25 euros and sees a price of between 28.50 euros and 31 euros as acceptable. (Reporting by Alexander Huebner; Writing by Victoria Bryan; Editing by David Goodman)