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Kerdi /"modern" membrane with cast iron drain

I am about to begin re-doing a shower on a cement slab -- that I had planned to do in 2001 -- finishing it with ceramic tile. (Someone had installed a 2nd layer of ceramic tile over a failed ceramic tile wall without fixing the basic problem -- chicken wire mesh (then plaster) that ended between two studs and the ends were not fastened to each other!) At that time, I gutted the area so that the studs and the slab are exposed and the curb is gone. I had a plumber install a new cast-iron drain, which is on solid with some sort of epoxy filling between the top of the pipe and the inside of the drain. (The old cast iron pipe/drain connection was very corroded.) For the new shower pan and curb, I had purchased a sheet of blue vinyl membrane (Composeal), membrane corners (Pasco), solvent-based elastomeric sealant (Compotite Elasti-Seal), flexible vinyl cement (Compotite).

Three separate, but related issues:
1) Since first planning this shower renovation, I have been concerned about minimizing the "bulge" at the corners where the membrane is folded. (At that time I installed pieces of 1x10 between the studs as backing for the lower wall area of the pan. Thus, unless I create them, there is no space through which to "stuff" the corners as some suggest.) Now that there are several types of thin membranes available -- Kerdi, Noble, RedGard, etc., I am wondering if I would be better off (easier?) to simply scrap the pan liner and fixings that I have and use a more "modern" waterproofing membrane? Kerdi seems to me to be the best, albeit quite expensive. Experience/ opinions/ advice?

2) Kerdi “requires” use of their proprietary drain. If I follow the same technique as shown in RedGard's shower pan construction diagram, seems like I could use any of the "modern" membranes with the a cast-iron drain as long as the membrane will stick to the top of the lower flange of the drain and/or be thick enough to allow the clamping of the top and bottom of the drain to maintain water tightness. Of course money is an issue, but so is my time. (I'm getting old enough that the "fun" of renovation is looking more and more like "work".) Experience/ opinions/ advice/ confirmation?

3) I'm considering having the height of the curb at an absolute minimum, possibly even eliminating it and raising the entire bathroom floor with a ramp at the entrance door for old age easy access. Thus, even the thickness of the membrane is an issue and it appears that I could eliminate the "top" mud layer that I had been planning by using a "modern" membrane with thinset for the ceramic tile applied directly onto the membrane. Experience/ opinions/ advice/ confirmation?

If you have read this far, I thank you. Some say I am too detailed in my explanations -- how to fix the watch when asked what time it is, but with something as critical as potential water leakage, I really want to be sure of what I am doing.

BTW, I have tiled a tub surround, used RedGard under tile at a doorway to eliminate water problems for the plywood floor underneath floor tile, etc., but this will be my first time doing an entire shower.

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