Fantastic website and resources here, kudos to all who have built this and contributed over the years!

Background:
I am renovating an existing 2nd floor shower, 3' x 3', so want to make sure it is completely waterproof. Previous problems were ++ mould growth on grout (mud base was very wet when I removed tiles) and green drywall was used as tile base so mould growth on removal). The shower will be butting against 3 exterior walls with insulation and existing plastic vapour barrier. Existing pan is made of wood with rubber liner, no overt water leaks to date. Existing mud base is present but does not extend to pan edges and previous drywall and vertical tile went all the way down to the pan bottom so no wonder mould problems. Existing drain seems to work, but want to figure how to integrate kerdi with existing drain or use kerdi drain system.

Proposed plan, options and questions to group:

Everything has been ripped down to wood studs, plastic vapour barrier in place, existing pan in place, existing mud base in place, existing drain in place.

1. Will cement board over everything, leaving 1/2" gap from bottom of pan to prevent wicking. Any preference to which type of cement board to use? Do I need to finish the seams with fiberglass tap and thinset or leave it if I install Kerdi?

There is a 1" gap from the pan/wall to the mud base which will become a 1/2" gap when I install cement board. Do I need to fill this gap in with more mud, or should I totally rip out the old base and (preferably) use the styrofoam base from a kerdi shower kit or have another mud based poured and graded.

2. If I rip out the existing mud base and use the kerdi shower kit I will obviously use the kerdi drain system with it. If I stick with the existing mud base, should I chisel out the drain area to install the kerdi drain and re-mud it, or should I try to integrate the kerdi system with the existing drain. I do not have access to the drain from below.

3. I am confused as to which type of thinset to use under the kerdi and over the kerdi for tiling. I know the manufacturer recommends unmodified, however other forums note that lightly modified thinset like versabase is best to use. Any opinions or experience here?

4. If I install kerdi over cement board over vapour barrier, do I have to worry about vapour lock between the vapour barriers, or should I remove the existing plastic vapour barrier assuming the kerdi and cement board is enough, or should I rethink about using kerdi altogether.


Another option would be to just re-cement board and retile the whole thing without kerdi, assuming the old system was pretty watertite to leaks below, this doesn't solve the problem of moulding grout however.

Lastly if anyone is in the Toronto area I would be happy to pay for someone's time to take a look and provide at least some general advice before proceeding too far.

Thank you all.

Bill

Welcome Bill,
First off, the pan is not built right to begin with, so it needs to go. Depending on which system you go with will dictate how construction advise is given.

Kerdi or any other liquid membrane system is by far the best option.

Right now you have too many variables to give accurate replies to the type of questions your asking.

You decide on what type of shower construction suits your skills and budget. Browse the web site and look at the different methods. Then come back and ask questions related to your specific choice of construction.

If you could post some photos thats always a big help. If you do that, a site visit may not be necessary.

Thank you Randall for your response, sorry for the busy first post.

Here are some pictures of where I am at now:







What I do want is a Kerdi watertight system, so whatever the means to achieve this in a quality manner I want to go with.

Re-looking at most of the information here and other places leads me to understand that one should use the Kerdi drain with the Kerdi system unless there is no practical way of doing so, so I think that answers my own question that my exising drain, mud bed and pan needs to go.

The questions that remain are:

Is there any preference as to type (modified or unmodified) thinset and as to brand of thinset for use under and over the kerdi? Practical experience welcome here.

Is there any concern as to vapour lock between the kerdi and plastic vapour barrier I have up?

I am pretty handy, but this would be my first shower, so if after looking at the pictures and someone with experience is in or coming to Toronto, I would be happy to pay for some help.

Thank you again,

Bill

Yes, remove the existing mud pan,liner and drain. You may have to remove a section of plywood around the drain to be able to cut off the existing drain and restub it for the Kerdi drain.
Purchase the new Kerdi drain before you start modifing the existing so you have the cutout templates and the actual drain to calculate the new drain pipe height.

So lets assume your going to use cement board.

Your going to run the Kerdi to just above the shower head so you need to remove the poly up to 12" below the final height of the Kerdi. At the verticle wall near the opening and to the right of the opening leave the same overlap of poly.(12")

If there are no plumbing changes proceed by installing all the cement board using the correct fastners. Leave the cement board 1/4" to 1/2" off the floor.

Cover all the curb with cement board but use thinset and fastners to embed the sill pc.

If your not clear on the next steps we will guide you once you get to that stage.

Use a quality unmodified like Mapei Kerabond to install the Kerdi and your tile.

Yes there is some concern with creating a vapor sandwich between two moisture barriers. If you were not using Kerdi, then you could leave the existing vapor barrier up.

Bill, what part of GTA are you in?

Thank you again Randall for the clear instructions and clarifications,

I usually like to help contribute to forums before jumping in with a question, but in this case I don't have the expertise yet.

I am located in south Etobicoke, I will try to send you an email Randall.

Thanks

Bill