Robin,
I have a working model of the Kingsferry Bridge (Isle of Sheppey) and it's carved from European oak so it's nice and sturdy. The wood finish looks great (if you're a woodturner) but I want to paint it in "concrete". If I had that self same formula that you've applied to your gate posts it will look absolutely spot on.
The gates are also made and I have the servers for them so hopefully I can get them hooked up to operate similar to yours.
Paul.