Yes Steve, no slurry coat. Not sure if zinc coating is resistant to the cement in backerboards but I would imagine it is. They use zinc to inhibit corrosion on steel exposed to the elements, but I would be guessing if I gave a resounding yes!
for a sand cement screed do i mix 4to1 building sand to normal blue circle cement and leave to dry before going over with concrete or will sand cement screed up to desired level do?
Know how to pick my jobs for a beginner!
No building sand you want sharp or river washed mixed semi dry as you said 4-1 to a maximum depth of 75mm. Do the concrete first then screed if thats an option for you