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Old 06-26-2009, 06:36 PM   #1
wtam
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is a pre-slope on shower floor really necessary?

Hi all,
Newbie here.

I did a lot of lurking through the liberry, and wish i found this site before i got my project going. I understand that the way to go on a shower floor is to pre-slope before putting in the pvc liner.

Question is.. what happens if there isn't a preslope?

Here are some details of the project.
Shower stall is ~56" x 32" with a bench seat ~14" deep at the back of that.

I had the plumber install the drain and pvc liner. He just put it the liner over the concrete subfloor and up and over the bench. Goes up about 10" off the back of the bench and the two sides off the floor.
Also wrapped the liner around the curb made of three 2x4's.

It got through inspections no problem as a simple leak test was done and the water held, so I had the cement backer board put in as well.

Was getting ready to tile and was introduced to the kerdi stuff so started doing more research (wish i learned about that kerdi stuff earlier too, but i guess it's too late now as i can't get a kerdi drain in now without cutting it all out).

So, before i have my tiler come in and put in the mortar bed, should i somehow fix the pvc liner to get a preslope in?
I just redid a leak test and it's still good, but after i drain the water, there are puddles in the base of the liner. If the mortar bed is done well and is sealed, does it matter the base isn't pre-sloped?

And if yes, any suggestions how to do this without ripping off all the cement backerboard and redoing the liner?

Thanks in advance...
Warren (as it looks like you guys like to know our names)
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Old 06-26-2009, 06:47 PM   #2
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Hi Warren,

a preslope helps the water slowly get into the weep holes so there is a constant movement of water escaping the mud bed. if the liner sits flat water can puddle and possibly form mold and other goodies.

the mud in your shower pan will get saturated within the first few weeks of use and stay damp with daily use.

water will get into the mud bed via the sanded grout.
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Old 06-26-2009, 07:02 PM   #3
wtam
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Thanks for the reply.

So any ideas on how to fix this without ripping it all out and doing it again?

If i put a kerdi membrane over the mud, would that help or would i just create a sandwich between the kerdi and the pvc liner (if water were ever to get through the kerdi).

Also, is there any way to use a kerdi system reliably without a kerdi drain?

Thanks again
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Old 06-26-2009, 07:08 PM   #4
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What Brian said Warren. You want that preslope. The good news is, you asked at the right time before the install. Take the board down pick up the liner and preslope the floor. You might be able to use the liner again. You also might find that the plumber didnt do such a great job going over the curb.

The liner on the bench isnt any good if you put a dozen screws through it fastening down a cbu. You'll need surface waterproofing there, either paint on or fabric on the seat and up the wall to keep water from getting behind it up high. On the curb too, hey, why not paint the whole stall and be done with it. There's probably no moisture barrier behind the cbu so you'll need it anyway.

You'll know when you remove the cbu.
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Old 06-26-2009, 07:13 PM   #5
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you don't want a surface membrane with a liner under it for the reason you said.

with any surface membrane be it Kerdi, Noble TS, Redgard or HydroBan you need to tie it into the drain correctly or its useless.
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Old 06-26-2009, 07:13 PM   #6
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Im still not a fan of putting 2x4's on concrete as a curb.
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Old 06-26-2009, 07:21 PM   #7
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me either Scott.

that's why here in Florida I like doing curb brick with the Kerdi membrane in a shower.
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Old 06-26-2009, 07:30 PM   #8
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He just put it the liner over the concrete subfloor and up and over the bench.
This is really a garbage way to do a shower bench. As mentioned above, that liner now has a bunch of holes in it from attaching the backer board. Without a surface applied membrane (bonded or liquid) it will leak and be a mess to fix/re-do.

Combine that with no pre-slope and I'd say re-do it before you tile. I can't think of a way to install a kerdi drain after-the-fact, that would be easier than just starting over.
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Old 06-26-2009, 07:42 PM   #9
wtam
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sigh.. i had kinda resigned myself to the fact i had to redo this.. and fight my builder over fixing it. But i guess i wanted to hear it from you experts.

Thanks for the advice.

now, since i'm ripping it all out.. maybe i'll just go for a full kerdi system shower.

Anyone know the going rate for a kerdi shower install? i'm in vancouver bc.

PM me if you want to quote on the job.
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Old 06-26-2009, 07:46 PM   #10
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Hi Warren. Like they say, it's best to have the preslope but not all showers start smelling bad that don't have them. I don't know why but some do and some don't. If the CBU is already installed on the seat with holes through the liner, I would probably start over. I would be real concerned about that.
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Old 06-26-2009, 11:49 PM   #11
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Do you cover airfare? or at least espresso from 49'th parallel.
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Old 06-27-2009, 08:45 AM   #12
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Warren:

I am no expert here but I have been through the same thing you have.
I was able to find clear diagrams and instructions online for my Oatey-brand drain that called for a pre-slope.
Also - and you should confirm this with someone else - these are the sections of the uniform plumping code and international residential code that I was told address the preslope requirement: u.p.c 412.18 and i.r.c. 2709.3.
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Old 06-27-2009, 09:29 AM   #13
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Good morn everyone
Since you dont have mud in yet and you dont want to remove board i would suggest you cut the pan liner out at base of tile backer ad preslope and then install sheetrock over curb and kerdi all. The liner at lwoer walls and bench would be open at both ends and i dont believe this would be enough to cause a problem.
What do you guys think?
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Old 06-27-2009, 10:39 AM   #14
wtam
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so i had my general, plumber and tiler in this morning and asked them what's going on here.. this was their combined response

1) don't need it as it's not necessary by code (note, i do have permits and did have this inspected and passed by the city inspector)
2) even though i have a flat liner, the liner is a filled with mud so water won't have puddling/pooling. What water that does seeped into the mud will wick from the mud into the weeping holes as that's the path of least resistance since the rest of the area is protected by the membrane
3) i have radiant heating in the concrete subfloor, so that will help in the daily evaporation such that there will be no standing water to mold.
4) worst case "puddling" is less than a 1/4 inch as that's the thickness of the drain clamping ring, but re-iterated it's not puddling but rather mud seepage/saturation which will easily evaporate during the day between showers.
5) this is how they have been doing it for 20+years with no problems and gave me the addresses of a couple houses he did 10+ years ago to check myself if there is a problem (note, my general is fairly reputable).


So what do you think? should i push the issue?
The builder seems somewhat willing to fix it (with some additional cost i'm sure)... but is telling me it really isn't necessary.

Thanks
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Old 06-27-2009, 10:52 AM   #15
wtam
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one other note, this is just a regular shower which will probably be used a couple times a day - no steam, just a standard stand up shower.

Other notes, the cbu was only nailed to the bench on the points that will be outside of the glass panels and mortared down on the interior, so no nails penetrated the membrane within the shower area.

there is a vapour barrier behind the cbu.

general also noted that before tiling is done, there is are several coats of sealer applied/painted to the whole shower stall... so the water is protected from "leaking" and will divert all the water that seaps through tile/grout and thinset into the drain. The sealer acts kinda like the kerdi stuff, just not as long lasting.. says i'll get 25yrs minimum out of this... if i kerdi, it'll be good for 50+yrs..

he'll personally guarantee the install for 25yrs that a) it won't leak and b) it won't mold (if i do some regular cleaning and proper maintenance (ie reseal the grout every 2yrs)

company has been around for 40yrs, but of course, can't be sure they'll still be around in another 25.
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