JanosK, on this video by Yvan he uses multiple sprays on the wheel and so I am with Setec, 2 sprays sounds a little on the low side. Don't forget the ONR will also dilute the Ferrex. As for efficiency, this is often not what people think it is. If a process needs to be done twice then it does not sound very efficient but more broadly efficiency also depends on what you are trying to do and why. A process in a high volume detail business could be very different to a business working on show cars and this is largely due to the expectations of the customer. Is your goal 'good enough', close of perfect or somewhere in the middle, efficiency is about finding the solution which will give you that goal