Spoke to laybond tech guy he said same as you, apart from he didnt mention degreasing, just light sanding.... is the sanding literally just to score the surface ? Also you mentioned a low strength compound..for what reason ?
the compound needs to be softer than the subfloor it's bonding to and asphalt is quite alot softer than a sand/cement screed
Magnesite flooring is electrically conductive and so an electrical resistance moisture meter will give a full scale damp reading even when the material is bone dry. Also, a small lump when held in gas flame will glow brightly, like a gas mantle at the edges. Yes youre right, its very sensitive to moisture too. i would put down an isolater membrane as merit says over arditex n/a or yellow bag then any sheet vinyl on top.
