It was a fairly decent day for Mercedes by recent standards as Michael Schumacher and Nico Rosberg ended practice sixth and seventh fastest.
The Brazilian Grand Prix also marks Michael Schumacher's last ever race.
"It was a reasonably good day, and we kept working on our planned programme", he said.
"However, the predictions for Sunday at the moment are for rain, so there may be totally different conditions then. We therefore have to see what we can make of today's data and transform it into a good qualifying and, even better, a good race"
"It was a decent Friday for us today", added Rosberg.
"There were difficult conditions out there because of the high track temperatures and the altitude which made it hard to find grip. However we managed quite well and, especially on the long runs, the pace was good. So I hope we can do better here than in the previous races. But it will be tough for us, and our focus is still on learning and understanding for 2013".