Looking to paint exterior of the house sand&cement finish was going to waterproof and then use a quality exterior smooth masonary what would you suggest?
We would not recommend to waterproof the render prior to painting.
Assuming the cement based render is bare, clean, dry, sound and prepared as detailed in the technical data sheet you could consider Wethertex AP77 Flexible Smooth Masonry Paint.
This can be mixed to many RAL, NCS or BS colours in a matt finish.
If the bare render is friable Wethertex ST1 Quick Dry Stabilising Primer should be used prior to painting.