I have a 4" concrete block wall that separates my bathroom and garage. Right through this block wall is a 3" cast iron vent pipe, which is totally embedded in solid concrete. Someone probably chiseled out the block wall to make room for it, then later on pour solid concrete around it. You can see where I painted red is the location of the vent pipe, I painted it so no one would try to drill anchors into it.

I needed to "build out" 2-1/2" from this block wall before I hang my cement wall board and tile for my shower area. Originally I had planned to actually build a 2x3 studded wall over the block wall, but the unevenness of the solid concrete patches, as well as the copper pipes running on the surface of the wall makes it tricky. I would have to notch so many places the wall may not be as solid as it needs to be.

So I started to change my strategy. I found five horizontal locations across that the wall is quite even and square, and I mounted strips of PT 2x4s across, secured with 1/4" Tapcons. As shown.







I then plan to mount 1x3 strips that runs all the way from top to bottom on those 2x4s. The 1x3s will act as furring strips where the cement boards (Durock) will mount onto. Then tiles over the Durock.

Will this work? Tile mounted on Durock mounted on vertical 1x3s mounted on horizontal 1x4s mounted on concrete block walls? Sounds like a lot of layers.

The 1x3s should they sit on the concrete subfloor, or pushed up against the ceiling to leave some gap below for the shower floor preslope?

Thanks in advance.

 

The 1x3's would normally be fine as you describe. However, your shower control valve will stick out too far in all probability for the trim to cover it. A better solution would have been to built stud walls with bottom and top plates and attach them to the floor and ceiling. Then your offset would have been correct.

 

I measured the shower valve's recess requirements min and max and that's how I arrived at 2.5". But I don't know if it is ok to attach the tiles to so many "layers".

 

If you got it figured out on the supply valve, then adding the furring strips won't present a "layer" problem for the cbu. The cbu will attach to whatever you have on a level plane for it to attach to, no matter the layers.

 

Thanks. I wonder, when I attach the vertical 1x3 to the horizontal 2x4, should I use 2" drywall screws or I need some other kind water proof exterior grade screws, like deck screws?

 

I prefer decking screws, but just because they are stronger and less likely to have moisture problems. Hopefully you won't have any moisture problem past the cbu. CBU, of course, use rock on screws as prescribed.
I gotta ask, is the red line a "his/hers" division point, or what???

 

The red line indicates the location of a 3" cast iron vent pipe embedded in solid concrete behind the wall. I painted it so no one would drill or shoot nails into it without knowing it is there.