No vapor barrier needed. You can use liquid nails if you want, but if you're already using tapcons, and you secure them properly through the plate and into the floor, it's not really necessary. You may want to consider using some type of washer to keep the tapcon heads from sinking into the wood.

You need a moisture barrier behind any wood that is in contact with masonry or concrete which is located below grade.

The barrier can be strips of poly or type S roll roofing.

I checked all the posts before my last reply to make sure there wasn't any reference to this room being located below grade. I checked again and still can't find it. Did I miss it somewhere?

Thank you for the responses.

The half of the basement to contain the shower is wholly above grade. The other half starts off at about 2 feet above grade and slopes down to 0. The house has a built-in garage with a walkout basement. (The link to the diagram that I posted July 31 does indicate that the shower will be above grade. I had wanted to embed the diagram as part of the post, but I haven’t figured out how to do that yet.)

From what I see now upon further reflection, that hadn’t dawned on me before, is that the situation may not be so totally black and white due to half of the basement being above grade and the other half being partially below grade by 2 feet and going to 0.

Please correct me if I’m wrong, but there doesn’t seem to be a need for a barrier in this case?

I’m curious about “ … consider using some type of washer to keep the tapcon heads from sinking into the wood”. I had planned to countersink the wall tapcons as I’ll be using drywall overtop.

My question is, would there be a problem with countersinking the base plate tapcons?

Thank you in advance for your responses.

There's no problem with countersinking them. The studs will be pretty sturdy since they'll be supported by concrete, block, or whatever they're stuck to. A base plate for a wall would just be a little more sturdy with a washer on the tapcon, and there's no need to counter sink it since it's inside the wall. I learned this from standing up some walls in my office that they're just a little more sturdy with the washers. It's not a necessity, just a little extra insurance. Keeps the wall from swaying back and forth so much while you attach it to the ceiling, intersecting wall, etc. In my case, some walls ran parallel to and between ceiling joists, so I had to brace it up, and the tapcons with washers held everything a little better.

Thank you for the responses. I'm still making plans and taking notes before I start anything. Thank you to everyone for the advice.

I’ll be using Kerdi with regular drywall in the shower. I would like to ask two questions about this.

• 1. Should the drywall seams be done with drywall compound and tape, some other product such as sheetrock 90, or should the seams just be left alone as the Kerdi will go over top?

• 2. Should I be using rigid foam insulation against the cement block wall. The bathroom is above grade, but there is a drive in garage on the other side of the wall? (There’s an attached diagram to this thread)

Thank you in advance for your responses.

Hello,

I’ve been doing some further research into question #1 above. I would like to report on what I’ve found with regards to the possible available options that I had identified.

1st option. drywall compound. An article I read says that these products are prone to mould and take a long time to dry. The author of the article suggests to conduct an experiment with pre-mixed drywall compound and water to see mould form in a few days.


2nd option. sheetrock 90. Mould is not as attracted to this product as it is to the drywall compound; however, the product dries very quickly. It is not as quick and convenient to use as the mud, but to me this is a moot point for someone interested in doing the job right.

3rd option. do nothing. A David Taylor, who I believe is affiliated with an internet tile supplies retailer, published an article on Feb 14, 2004 in which he states:
"The drywall does not need any special preparation before the application of the Kerdi membrane. Joints do not have to be taped or mudded and there is no need for extra bracing or notching of the wall studs to accept a vinyl pan liner."

Based on the analysis presented, I believe the best way to proceed would be to leave the drywall seams alone which boils down to option 3.

Any comments from the pros?
(question 1 or 2)

Thank you.

You didn't ask for comments from the amateurs, but I'll throw this in anyway. Some of the drywall I use has the long sides tapered off in thickness for about the last two inches. This is so the seams can be taped and mudded without any buildup. If your drywall has the same feature, you may want to fill it in with something (one or two layers of thinset) to make it flat for the Kerdi. Otherwise, the indentation where the two boards meet will telegraph to the Kerdi, and you'll be trying to fill it in when you put the tile up. It'll be easier to fill in before the Kerdi goes up.
RE question #2, what would be your reasoning behind the use of the foam insulation?

Buzz, the exterior walls marked as Neighbour and Built-in Garage need to have insulation and a vapour barrier by code.
If you use styrofoam insulation then a vapour barrier is not required.

Here's a photo of a job similar to yours.


The exterior walls are cinder block and brick. I insulated with foam board and placed the strapping over the foam panels. It's a complete thermal break when done that way.

Hello,

Kman, sorry if I may have offended. I had meant anyone. To me and compared to me, anyone is a pro. But, you are absolutely right, mea maxima culpa for the choice of words.

#1 Thanks Kman. Excellent observation and point you make about the tapered ends and the use of thinset.

#2. Kman & RC. I was having problems deciding if I had an external wall on my hands and thus possible potential air infiltration, ambient vapour and moisture wicking issues. The block wall is at the back of the garage, but the garage does open up directly to the outside. It, the garage, does get pretty cold during the winter and there is moisture in the air, especially on hot humid days. An interesting experiment I’ve read is to tape a piece of clear plastic to a wall and check for condensation in a few days. RC thank you very much for the picture and for setting me straight. The wall marked neighbour isn’t really and exterior wall as I’m in a semi-detached house and that wall is shared between my neighbour and myself. It is not exposed to the outside.

The foam will prevent air movement in the wall cavity and thus prevent cold air from meeting warm air. Condensation forms when cold meets warm. Condendation will in turn lead to the creation of mould.

Thank you.