Hi everyone,
First post here - please be gentle

I'm in the midst of doing a basement bathroom with a custom shower. I have 2 questions which I'm hoping to get proper answers for:

1. Can I have a mortar based shower bed, with the rubber waterproofing membrane, along with Kerdi on just the walls? What would I do at the junction of the walls / shower bed?

The reason I ask, is that the plumber has already installed a clamping type drain in the shower (OS&B, model SD45) and will be installing the rubber waterproofing membrane when he returns to finish up the job. I know that the complete Kerdi system is best, but short of ripping up the concrete/drain, there isn't much that can be done (I think).

2. From what I've read on the site, it appears that the order for the shower base should be: "pre-slope" mortar base, rubber membrane, final sloped base. What if the pre-slope is omitted and the rubber membrane laid down directly on the concrete floor of my basement, then the mortar bed is created, sloping towards the drain? Am I asking for trouble? The reason for this is that the plumber said that he would be laying the membrane the next time he comes over.

Thanks to everyone in advance.

You are correct, it's preslope/liner/final mud bed.
If you continue with your plumbers advise and work you will have trouble later.(trust me)
The tile setter should be the one who installs the membrane.

If your looking at doing a kerdi system then it really should be Kerdi all the way.

Tell the plumber to just leave the membrane material if you have already paid for it and have your tile setter install it.

I guess I should ask, are you installing the mud base and tile or someone else?

I just finished a shower where the plumber installed a clamping drain, against my wishes. (He did this after moving the drain over a couple of feet for me.) I used an inside pipe cutter and cut off the clamping drain and installed the Kerdi drain. I didn't have to pour a preslope, I didn't have to buy a liner, and, at least in my case, I didn't have to buy the clamping drain. When all was said and done, eliminating those three things probably saved me enough money to buy the Kerdi drain, and I built a much better shower than using the conventional method. I've done two Kerdi showers now, and I don't believe I'll do one the old way ever again.

Hi RC,
At the current moment, I'm trying to find someone to install the mud base/tile. That's probably a good idea about leaving the membrane off.

Hi Kman, I'm assuming that by not pouring a pre-slope, that you used the Kerdi shower base as well or did you just do a mud base and then Kerdi over the whole thing?

I think I'll ask my plumber about possibly cutting out the clamping drain and installing a Kerdi one.

It seems that Kerdi is the way to go and is considered the "new" method (complete system with Kerdi drain). However, there are a lot of people still doing the classic way with pre-slope, membrane, final slope. I guess I need to ask, which way is better (in terms of longevity)? Also, if doing the "classic" method, how are the walls waterproofed? Using DensShield or Durock/Redguard?

I've been reading so much that my head is spinning. At least I have the luxury of waiting to decide what to do on the walls (since I'm doing that myself).

Thanks again to everyone for your help.

I did a mud floor and Kerdi over the whole thing. In terms of longevity, Kerdi is much better in this way:

The conventional method (PVC liner) allows water to saturate the mud floor that is underneath the tile. That water is directed to the drain by the liner, but there is moisture there for a while, which allows for bacterial growth. The same goes for the walls if they're done with durock or hardibacker. The CBU gets saturated but eventually dries out.

With the Kerdi system, the tile is adhered directly to the Kerdi, so any moisture that gets through the grout hits the Kerdi and is either directed to the Kerdi drain or evaporates very quickly. This means there is very little or no chance of bacterial growth. This is the primary reason that Kerdi is the better system.

If you decide to use the conventional method with the liner and clamping drain, you can use durock or hardibacker on the walls and waterproof them with redgard or laticrete 923S. If you go with Kerdi, there's no need for any waterproofing.