concrete floor

[rodsretreat]

had to take up old concrete floor which was laid on rubble going to reconcrete an area of 4metres by 2meters can i lay viscuine straight onto rubble then reconcrete should i use a sand and cement mix of 4to1 ratio or make a concrete mix with sand gravel cement how much will i need to do this area at 40mil thick willthis be deep enough after concreting on this im going to lay warmup insulation boards then underfloor electric heating then tiles any other advise greatly welcome