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Shower membrane(s) for tiled shower over slab on grade?

R

Ryan Hughes

Registered User
Joined
Apr 29, 2020
Messages
5
Location
Boulder, Colorado, USA
I am working on a project in Colorado, under the 2018 ICC codes. We have a walk-out basement with a slab on grade. In the bathroom, I've shown a curbless shower with a tile floor finish, pitched 1/4" per foot to a linear drain along the far wall. I've spec'd the Schluter family of products for the walls, floor, and linear drain, with their heat mat + membrane product set on top of the sloped concrete, with tile set on top of the sloped membrane. This is the exact same membrane system I'm using on a wood-framed bathroom on the second floor, which is wood framed.

My contractor is telling me that I need a second membrane under the slab on grade to meet current code. This seems insane--how can the code approve of this Schluter waterproofing membrane system upstairs at a wood-framed area, but somehow it doesn't cut it at a ground-floor shower that is on a concrete slab? He has not been able to cite any code section to back up his statements. Anyone here have experience with this code, supposedly requiring two membranes for tiled showers set over a concrete slab?
 
Undoubtedly your contractor has twisted up something to believe that this is necessary. Go ask the local AHJ.
 
Hope this is authorized ... you might try posting your question at johnbridge.com, it is an excellent source for all tile questions. They won’t know code, but they know everything about tile and manufacturers requirements.
 
Paul Sweet said:
Is he thinking of a vapor barrier rather than a waterproof membrane?
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Great question. I have a typical 15-mil Stego vapor barrier beneath the slab in my specs, and he's insistent that it is the shower membrane required to be beneath the slab. I think he's just thoroughly confused. I've done showers with exposed concrete topping slab floors, and of course they need a sloped membrane to tie into the drain beneath the topping slab (which is essentially acting like a really thick tile in that scenario). I'm thinking maybe he is forgetting/ overlooking that we have a tile floor over the sloped concrete slab. Hoping to resolve this on a conference call we have set up tomorrow. Thanks again to everyone for the replies!
 
417.5.2Shower lining.
Floors under shower compartments, except where prefabricated receptors have been provided, shall be lined and made water tight utilizing material complying with Sections 417.5.2.1 through 417.5.2.6. Such liners shall turn up on all sides not less than 2 inches (51 mm) above the finished threshold level. Liners shall be recessed and fastened to an approved backing so as not to occupy the space required for wall covering, and shall not be nailed or perforated at any point less than 1 inch (25 mm) above the finished threshold. Liners shall be pitched one-fourth unit vertical in 12 units horizontal (2-percent slope) and shall be sloped toward the fixture drains and be securely fastened to the waste outlet at the seepage entrance, making a water-tight joint between the liner and the outlet. The completed liner shall be tested in accordance with Section 312.9.

Exceptions:

  1. 1.Floor surfaces under shower heads provided for rinsing laid directly on the ground are not required to comply with this section.

  2. 2.Where a sheet-applied, load-bearing, bonded, waterproof membrane is installed as the shower lining, the membrane shall not be required to be recessed.

  3. 3.Shower compartments where the finished shower drain is depressed a minimum of 2 inches (51 mm) below the surrounding finished floor on the first floor level and the shower recess is poured integrally with the adjoining floor.
 
Glenn said:
Here is an article on the subject in the Know the Code column in Fine Homebuilding Magazine. https://www.finehomebuilding.com/2019/05/09/284-site-built-shower-pans

This lays out the code method, not the Schluter system. You do not need a shower liner beneath the concrete floor.
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Nice, thank's Glenn! Your's was one of the first (and most helpful) items I found when google searching this. I am now well-armed to cite code and code-experts in my meeting with the contractor later this morning. Should be interesting....!
 
Ryan Hughes said:
Nice, thank's Glenn! Your's was one of the first (and most helpful) items I found when google searching this. I am now well-armed to cite code and code-experts in my meeting with the contractor later this morning. Should be interesting....!
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Let us know how it goes and what you find out. Good luck!
 
I do not think your going to have any push back in this meeting as there is no code language for this supposed requirement, which makes absolutely no sense on so many levels.
 
Reporting back, as I suspected, the contractor was confused, not looking at my details, and comparing apples-to-oranges. They built a past project with a slab-on-grade shower, and had to use a membrane under the concrete shower floor--which isn't surprising per the code--the concrete finish floor is essentially just like a really thick tile at that point, and still needs a membrane beneath it. He was fixated on that project, and not listening/ looking at the details and realizing that we had tile over a membrane (Schluter Ditra Duo) set over sloped concrete. It was great to have all the feedback above to reference on the call. Problem solved! Charging the client add services for having to waste my time on this BS....
 
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