Urgent - PVC Shower Pan Membrane Punctured By Screws - Potential for Leaks - Advice Soliticted Please

I am having my shower torn out and completely rebuilt.
The trademan who is doing this (and who has done exceptional work for me in the past) has installed a PVC liner 7 inches up the sides of the shower and over the curb.
However, when he installed backer board over the PVC liner, he installed screws into the backer board that were about 1.75 to 2.00 inches above the bottom of the liner where it rests against a sloped subfloor, piercing the PVC liner at that level 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 by the time the tile is installed.
This trademan says that he installed a bead of caulk to prevent the PVC liner from leaking where the screws penetrated the liner, but I am still extremely concerned that integrity of the PVC shower pan has been compromised by the screws that pierce it.
It is my understanding that the PVC membrane should NOT have been punctured at a point so low to the bottom of the pan.
I would also like to know what would happen if the PVC membrane on top of the curb is pierced by screws when backer board is installed on top of the curb. Will this create create a potential for leaks as well?
If screws should not pierce the PVC vinyl membran, what is the appropriate way to fasten backerboard over a PVC liner? Does one just not fasten the backer board to the wall at the the bottom or what?
Am I justified in being concerned about the potential for leaks?
Please respond ASAP as the trademan has not installed the tile yet, but plans on doing so very shortly.
As I wrote above, this trademan has done superb work for me in the past, but this is the first PVC shower pan he has ever installed and it's possible he may not be fully aware of all the details to follow in installing one that is absolutely leak proof. Thank you.
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The potential for leaks where nailed 2" up is a real concern if the water does not drain out completely. Those holes will be less than 1/2" above floor. How did he get a bead of caulk under the backer board? Sounds like B.S. Make him replce the liner as there should be no holes in it that low. The holes on the curb shouldn't be a concern because they will never be submerged, I hope.
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hwm54112
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Geezus Keyrissttt ----> Calm down !!!!!!!!!!!!!!!
It's only a little water... Not hurricane Katrina. So a few gallons of water run down under the shower, big deal. The worst that can happen is the ceiling underneath will collapse, the floor will rot under the shower, and some day you will fall thru the floor into the room below, which is only an 8 to 10 foot drop. Not a big deal when you consider how some people have fallen 3 or more stories in recent hurricanes, and some of them even survived. Besides that, the drain pipe will likely remain intact when you fall, so you will have that to grab on the way down.
Trust your trademan, he's the expert, and it's only your money....
If however, this really bothers you, put some duct tape around the bottom of the walls before he finishes the job. Duct tape holds the world together so you can feel much safer, knowing duct tape came to the rescue, and if the floor does collapse, the duct tape will hold tight and strong, and save your life.
Rondo
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Its fine. No worries. Just ask for a guarantee from your man. Say, 1 year, no leaks OR tear it out and attach 3" further up wall. You man will go with warrantee. Get it in writing. W/o seeing it, but as you described it, there will be no issues if the tile and grout are done properly.
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