That does NOT sound like a proper plan!
A conventional shower pan is made up of three layers before the tile goes on:
- a presloped mudbed
- a liner on the preslope (flood tested to verify it doesn't leak!)
- a setting bed of mortar that you add your tile to.
Deck mud is mad up of a lean sand:cement mix of around 4-5:1, mixed with enough water to hydrate the cement and allow it to bond - wet beach sand is a good analogy for its consistency. When it cures, it will still be a bit grainy on the surface, but be porous, and fine in compression (porosity is needed to allow the moisture to migrate through it to the weep holes of the drain that you've kept clear!).
There are some alternatives, in fact the TCNA guidelines contain lots of them, but it sounds like you're trying to do a conventional one, and it does NOT sound right. Trying to reinvent the wheel isn't a good idea until you've got lots of experience and can afford failures, which few DIY'ers can afford.
There are good reasons why things are done in a particular way, and it would be unusual for an individual to figure it out on their own. Lots of what if situations.