Al wrote:

I am having my shower torn out and completely rebuilt.

The trademan who is doing this has installed a PVC liner 7 inches up
the sides of the shower from the and over the curb.

However, when he installed backer board over the PVC liner, he
installed screws into the backer board that were between 1.75 and 2.00
inches above the bottom of the liner where it rests against a sloped
subfloor, piercing the PVC liner at that point behind the backer board.


He intends to lay down a layer of mortar on top of the PVC liner to
create a sloped surface to lay the floor tile on. Thus, the height of
the screw holes (and the punctures in the PVC membrane) will be even
closer to the finished shower floor after the file is installed.

This link has details of shower installation, and suggests your concerns
are right:

http://www.thetiledoctor.com/howto/showers.cfm