I found with this sawdust like flock, the PVA glue would show and soak through the flock. A second dunk in the flock tub just made sure the base was well and truly covered in colour with a nice thickness to it. Any mistakes or patchy areas at this point can be covered over in later stages so do not worry about details. Sometimes the metal bases of figures can still be seen easily after the first layer, but do not worry.
The great thing about flocking bases is that it allows you to do whole armies in one go and quickly too.