shower water proofing

I am completing a new shower enclosure. I've finished the mortar bed, installed the vinyl liner and a new valve for the fixture. However, I'm wondering about extra waterproofing. Is there any harm to putting an additional "insurance" liner under the Hardiebacker? For example, I have a roll of the liner I used under the mortar bed which I'm thinking about affixing to the studs under the backer board. I also have some DAP (3.0) Waterproof Caulk I was going to use on the backer board joints prior to affixing the alkali-resistant tape. Is there any down side to taking these extra steps? Thanks, Tom

I've finished the mortar bed, installed the vinyl liner and a new valve for the fixture.

In my crystal ball, I see a hammer in your future.

Is there any harm to putting an additional "insurance" liner under the Hardiebacker?

If you were led to believe that Hardibacker will provide you with any waterproofing at all, you have been seriously misled. While it will never be affected by the shower water, it will always be happy to allow water to go right through it. Showers need either a moisture barrier of 4 mil plastic sheeting or 15 lb roofing felt installed over the framing and overlapping the liner prior to installing the cbu or, a surface waterproofing membrane can be applied to the cbu prior to installing the tile.

I also have some DAP (3.0) Waterproof Caulk I was going to use on the backer board joints prior to affixing the alkali-resistant tape.

Just thinset and tape them. Your moisture barrier or your surface waterproofing will take care of water issues. You do use caulk where the tile meets tile at the wall intersections though.

Let's backtrack though. Shower construction goes sloped mud bed, then liner, then moisture barrier, lath for the curb (no cement board on the curb), then install the cement board with no fasteners in the lower 8 inches, then your settng bed of mud to lock in the lath for the curb and the lower portion of the cement board to the shower framing.

Is there any down side to taking these extra steps?

The thickness of the liner in the corners will cause your walls to be out of plane and make for bad looking corners, especially with a pattern or diagonal install or large format tile install.

Did you build a bench in this shower?

Thanks for your reply. To be more clear; I laid down a single layer of roofing felt as a slipsheet over the subfloor, then built a sloped mud bed and installed the PVC liner (Oakey brand). The cbu is cut to size and ready to be installed. Based upon your recommendation; I will install 15 lb. Roofing felt, which I have on-hand over the framing. Curb is built and lath is on-hand as well. I had no illusions the cement board provided any moisture barrier but noticed there was no other moisture barrier apparent behind the original shower walls when I pulled them out; which led to my question in the first place. I've gotten different answers from a number of professionals but, I'd rather be safe than sorry so, I'll definitely install the moisture barrier. I'll shim the cement board to get the walls on plane. My shower looks almost exactly like this one:

http://www.ontariotile.com/preslope.html

Now that I look at it again; I only see the moisture barrier on the back wall but, I'll install on all three walls.
Please let me know if you have any other thoughts.

Hi Thomas,

I would like to reccommend that you use Schluters Kerdi material for a pan liner. What is nice is even though you have the mud base in place, it can be use over the top, with the premade corners available to really water proof your shower pan. I also reccommend use on the walls. It can be used over standard drywall.

I attended their seminar as an installer, and the first thing wr did was make a cardboard box cooler for the class room, and it never leaked. I use it on 90 percent of all tub and shower installations my comapny does. If you use this product you need not put a vapor barrier in for it has its own vapor barier in the material. Check it out on their website. [schluter.com]

Good luck and I am here if you have any questions.

Linda

Very good advise Linda. I agree Kerdi is the only way a shower should be built.

I also recommend checking out the Ontario Tile link above, Harry has done a fine job there. While you're at it, see a few Kerdi showers I did here. http://picasaweb.google.com/tile4youinc

Jaz