Alternative to fermacell fine surface treatment

[tck1985]

I’m preparing NoMorePly cement boards to be microcemented over as part of a bathroom renovation. FST has been recommended on here to fill the screw heads / boards joins. I’m struggling to get hold of any locally and the delivery cost online is as much as the product. Can anyone recommend a suitable alternative? Would Toupret fine surface filler work ? 

[PeterW]

Either Toupret or Alabastine filler are fine