Shower Vapor Barrier

['65 corvette]

I have a house that was built in the early 1950's. The walls are a plaster board that vary in thickness, 5/8'' to almost 3/4''. I am putting in a shower surround and am hoping that I can leave the existing sheetrock up. My reasoning for this is where the tile will tie into the sheetrock, I don't think it will transition cleanly.

My first question is- Can I leave the existing sheetrock up, use 15 lb felt as a vapor barrier, and then attach my hardi backer board over it? I am having a hard time getting a straight answer on leaving the existing sheetrock up.

Second question- I formed the curb up, applied felt paper to the sub floor, then metal masonery lath on top of it. I poured the pre shower pan at 1/4'' per foot of fall, using pre pitched plastic guides for my slope. The bedding material was a 4 to 1 bedding type grout. I then applied my rubber membrane and water tested for 24 hours, no leaks. However, after the water drained, I noticed an ever so slight (about 10'' diameter) puddle near one side of the drain. I checked the entire pan with my torpedo level for fall, the bubble was buried on the correct side, except for where the water pooled. I had downward fall in that area, but not much of it. Part of the problem looks to be where the rubber membrane is folded around the drain flange and is sticking up ever so slightly in that area. When I push down on it, it drains better. Is this going to be an issue.....and when I pour the final mud bed, will it keep the membrane pushed down around the drain flange?

Thanks Joe.

[Houston Remodeler]

Joe,

Welcome to the forum.

1- Yes you can leave the old drywall in place and install a waterproofed shower over that. But pay special attention to the bottom edge. You don't want to get water wicking up from the shower floor / tub ledge into the drywall from the bottom.

2- If the slope is proper, and from your description, when the mud is packed on the upper layer, that setting water will be wicked up into the mud bed and spread itself out. You're fighting the surface tension of the water and the liner, which will not be such a huge factor.

['65 corvette]

Thanks Paul!

I really appreciate your advice, I contacted my local building code inspector today- He agreed with you.

Thanks Joe.