PSP (Metallic Panels)- Request your contribution
 

have a technical problem to solve on an airfield used 25 years ago by USAF. A tarmac is made with those metallic plates (PSP), the "PSP" are rusty but seem in workable condition for General aviation particularly a Flying School. I have seen on old photos that the Tarmac was black.
My questions are:
Has anybody information about maintenance of those PSPs? Have they to be painted and do we need any specific paint? What is the method used to take out the grass (Any specific chemical weed killer -compatibility with those iron plates?)
if we put a layer of concrete or asphalt what are the risks of cracks?
Any experience on utilisation and maintenance appreciated.
Thanks