Yes it is. However the substrate must also be suitable. So if you have a solid base (such as a concrete screed) then the microcement will go straight over the top.
If the substrate is a timber floor then it will need to be prepared first. We recommend Hardie Backer but there are other similar systems on the market. Attached is their installation guide.
hardiebacker board applied to floor ready for microcement application 
hardiebacker board applied to floor ready for microcement application 
hardiebacker board applied to floor ready for microcement application 
hardiebacker board meeting shower base in readiness for microcement application 
taped hardie backer board ready to receive microcement 
microcement applied over hardiebacker board