HOCKENHEIM, Germany - Michael Schumacher blamed himself on Friday after he walked away unhurt from a heavy crash during the second free practice session for the 2012 German F1 GP.Schumacher said he was not concentrating properly in difficult, wet and treacherous conditions and lost control of his Mercedes car when it ran over a white line on the circuit.HEAVY DAMAGEIt was a major shock for the crowd in the stadium section of the Hockenheim circuit with four minutes remaining in a session topped by controversial Venezuelan Pastor Maldonado in his Williams. His car suffered heavy damage to all four corners and the practice session was red-flagged.Schumacher said: "Basically I've not been fully concentrated. I was on the radio and I was doing some other changes to the car and touched the white line. It was my own fault."Schumacher finished 23rd on a very tricky day for the teams, with rain coming and going both in the morning session, topped by Briton Jenson Button in a McLaren ahead of his team mate and fellow-Briton Lewis Hamilton, and the afternoon.The 43-year-old-German conceded that the changeable conditions meant the day was not too useful to him in preparing for the weekend when he hopes to lead Mercedes' bid to grab a podium position."It didn't help us a lot, because the conditions were so inconsistent that we couldn't learn a great deal," he said. He said, however, that it was worth running in the wet as qualifying is also expected to be hit by rain on Saturday."It is what it is, so you have to make the best of it. We are going to qualify probably in wet conditions so that's why it makes sense to go out and try the car and get the set-up right and so on."But it's guesswork for Sunday, definitely." Stay with Wheels24 for the 2012 German F1 weekend.