i wish to lay 19mm full length yellow pine floorboards on my fully dried 70mm screed.I have allowed 38mm from top of screed to top of finished floor level thinking that 19mm wpb plywood would be ok as a sub floor to attach 125mm boards to.What would be best way to fix ply to screed/boards to ply?.I was told by someone that i could anchor nail the ply and secret nail[at shallow angle} the boards -is this a good idea?.