For information on how to build a water tight conventional shower pan, take a look here:
achieve satisfactory results using either conventional built-up shower pans or Kerdi and similar systems, but based on my experience inspecting tiled showers you are more likely
to get a satisfactory result using the latter - it's not that the former system is especially hard to do, it's just that it's becoming harder and harder to find people with the skills and experience to do it properly.
One other thing to consider: there is a temptation to assume that because a shower pan is being installed on a slab, installation is less critical.
However if somebody is installing a tile shower on a slab there is likely going to be finishing the floor surface outside it, and you are already going to have all the other issues and concerns involved in selecting and properly installing a satisfactory covering material on a concrete slab - a material inherently prone to cracks and often in a below grade location especially subject to water intrusion.
Water leaking under a slab from a defective shower pan only increases the likelihood and potential severity of problems with floor coverings, and you are not going to have the option of coming at such problems from below to correct them.
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