Multi-layer Alodining

Dear members,

Is there any use of applying Alodine for several times one layer over another, provided the previous layer aged for a week or so?

I noticed the corrosion current grows after aging (probably due to cracking); also I read articles according to which Alodine C6100 doesn't provide full cover especially near grain boundaries and intermetallic particles.

Will the next in series Alodining destroy the previous coating or, it will rather overcoat it? I have some doubts about hexafluoric acid...

I treat aluminium with Alodine C6100 (Hexafluoric acid, Zink-hexafluoric silicate, Chrome Trioxide and Ammonium - 2 fluorosilicate composition, with Ferrocyanide initiator and Molybdenum accelerator).

Thank you!