Need a little advice, building shower pan

[tmy23]

Greetings. I am about set to begin building the shower pan for a tile shower in a master bath conversion of what was a nursery, in a 130 year old victorian. Rough in's are done, subfloor secured, walls now straight, and will do framing this weekend, pour and form the shower pan next weekend. Here are some questions:
- Seems to me sill height is predicated (to a degree) on the thickness of the mud bed. The shower is 4' x 5'. I didn't want to cut into the joists which run cross the project, so roughed for an "end" drain, will probably put in a linear drain, seems to make the slope question simpler. Anyway...What is the minimum thickness (drain end) for the two mud layers? the slope will be 1.25 inches across the 5' dimension, so if I am 1" at the drain end, then I'm 2.25 at the top, then another 1" finish mud on top of the rubber barrier takes me to 3.25 at the top. BUT I don't know whether 1" at the low end, and then a uniform 1" for the top layer is enough. How high above the final tile height should the sill be?

Next question, I've been reading that generic Sakrete sand mix is acceptable for the mud layers, but that I have to pour the 2nd layer (rubber and then 2nd layer) within 16 hours and then tile within 16 hours on the finished layer or wait 28 days. Do I have this correct?

thanks in advance for all your help!!!

 

[Jadnashua]

There is some disagreement on the minimum thickness, but industry guidelines call for a minimum layer of 1.5" for an unbonded mudbed. Some manufacturers will warranty their material for less. If overall height is really an issue, had you considered use of a surface waterproofing membrane such as Kerdi, or NObleCS, or Hydroban sheet? If you use one of those, you only need one layer, then your membrane, then the tile. You'd need a compatible linear drain to match up with the membrane chosen.

If you're going with a conventional liner, it's harder to find a linear drain designed for that than a surface membrane. And, if you go with a conventional liner, you want to add blocking between the studs to support the liner and provide a place to tack it in place. You should notch them as well to allow for the folding of the corners and not produce a bulge there. If you choose Kerdi or Hydroban sheet membranes, you can use drywall on the walls, since once the membrane is up, it is behind that waterproofing membrane...both of those companies have run the compliance tests to certify performance when using that as a backer with their sheet membranes (none have passed or tried with liquid applied ones).

You can set tile the next day over a mudbed. If you use a surface membrane, they want 24-hours cure time before you can flood test it, then you can tile it.

You'll get lots more review and probably more timely responses if you ask this sort of question over at www.johnbridge.com where all they deal with is tiling.