What thickness of sand & cement?
Say 1/2" = 12.5 mm = 0.0125 m
x 8m2 = 0.1 m3.
Sand is 1600 kg/m3 dry, so about 160 kg which is about 3 bags.
Anyway I would have thought that just by looking at that area, 3 or 4 bags would be a good guess.
JD, March 2009