Valtteri Bottas says confidence was building "lap-by-lap" in his Mercedes during practice at the French Grand Prix.

The Finn ended Friday fastest as the Brackley-based team once again established themselves as the dominant force at Paul Ricard, leading teammate Lewis Hamilton by four-tenths of a second.

However, that gap was flattered by a mistake from the Briton which was one of many on what Bottas admitted was a tricky day. 

“It was not easy in the beginning; everyone struggled in the morning because the track was much more slippery than usual,” he said.

“But the track ramped up quickly, I could feel big gains on a lap-by-lap basis, especially in the corners.

“The more the track improved, the better the balance of the car felt, but despite the balance issues, the car was quick out of the box which is always a good start."

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“We've made good changes between the sessions and I felt much more comfortable in FP2," he said initially "But it's really warm out there and it will only get warmer, so tyres are going to be on the limit, especially on Sunday.

“We still struggle with the balance over the course of the entire lap, so we'll have a good look at the data tonight to see what we can improve for tomorrow.”