Concrete shower pan; do I need a liner?

Discussion in 'Shower & Bathtub Forum & Blog' started by Alan Wheeler, Feb 14, 2017.

  1. Alan Wheeler

    Alan Wheeler New Member

    Joined:
    Feb 14, 2017
    Location:
    Cayman Islands
    I just removed the old tub from my bathroom and want to replace it with a walk in shower. The shower will sit on a poured concrete floor. To form a sloped shower pan would normally involve laying a sloped mortar base then laying the plastic water barrier and then laying a final sloped mortar layer before tiling. My question is given the floor is already concrete can I just lay a sloped mortar bed and tile on top. I would prime the concrete floor and then lay the mortar.
    I also need to make a curb for the shower which I believe is normally done by using 3 lengths of 2 by 4. Is there any reason I can't just pour the curb on the existing concrete after priming?

    Thanks in advance for any advice

    Alan
     
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  2. JRC3

    JRC3 Member

    Joined:
    Sep 27, 2016
    Location:
    S.W. Ohio
    It will need to be lined or it will wick into the slab and studding. The liner also makes the walls around the pan water-tight, that's why the liner normally goes up at least 3" above the pan behind the tile and backer material. Moisture gets behind the wall tile and is eventually caught by the liner. Same applies to the curb.

    Picture water damaged framing, moisture in the floor coverings in the rooms next to it, and mold everywhere. Basically same rules as if it was over floor joist.
     
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  4. Alan Wheeler

    Alan Wheeler New Member

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    Feb 14, 2017
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    Thanks I think that's a definite for the liner. How would I attach liner to the wall? Would liquid nails and then tile directly over it work? Is the metal mesh layer needed? Thanks
     
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Typically, you'd just nail the liner to the supporting walls, but if they're concrete, that won't work. In the USA, code says no penetrations 2" below the top of the curb (so, 3" is good, which gives you an area to nail into and still remain above the minimum). You need something that will allow you to bond tile to it over a traditional liner. That's typically cement board (cbu) which may or may not be available where you live and isn't designed to be fastened to cement walls. An alternative would be to do a mudded wall, which you might find people around that do this regularly. You might be limited on what supplies are available, but you might check to see if something like Kerdi is available where you live. It's a waterproof, tileable membrane. You'd make your preslope, then install the Kerdi on it to include the walls and over the curb. Then, the entire shower is waterproof right beneath the tile rather than just the pan. Check out www.schluter.com to see some h0w-to videos, and if they distribute it where you live. There are other choices. One major error many people make is how they construct the curb. You can't put your waterproofing over it, then nail cement board onto it...that just leaves lots of holes!

    Many people think tile is what makes a shower waterproof...USA building code (and most of Europe and many other places) recognize that they are not...the liner is what makes things waterproof, and gravity needs that liner to be sloped to the drain for it to dry out. A shower should not damage anything even before you tile it (but would make tiling it later tough because of soap scum and other contaminants!). Tile is the decorative, wear surface, not waterproofing.

    Check out www.johnbridge.com for some further help on building a shower.
     
  6. onehomeowner

    onehomeowner New Member

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    Aug 24, 2019
    Location:
    Houston
    As a followup, what if you were to waterproof the concrete using a penetrating wood and concrete sealer (which is also applied to the wood studs), would you still need a liner?
     
  7. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    This is my shower and the work was performed by a licensed plumber. The original slab was recess 2-3" below the floor. The old shower had a mortar bed and sloped to the drain with tile. The shower floor was about the same as the finished tile but had to step over about a 3" curb. For the remodel this motor bed was removed. I'm not sure if the original concrete pour was sloped or had to use mortar to slope to the drain but the walkin is about a 2" step down. The plumber had an issue that it won't meet code but the designer said that it is OK and has been done before.

    The plumber placed a rubber stopper into the drain pipe that you pump up to block the water from draining. A few inches of water was placed into the rough in. Orange County, Fl plumbing inspector passed it a few days later and I left the water in it for about a week. It never leaked.


    Click on picture for a larger view.
    UNADJUSTEDNONRAW_thumb_2df.jpg UNADJUSTEDNONRAW_thumb_2de.jpg
     
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    That method would NOT meet industry standards.

    Neither concrete nor the tile nor grout are considered waterproofing. The wall studs will be sitting on the slab. Without a liner, required to go up at least 2" above the top of the curb, how would you protect moisture from attacking them? Plus, being level, how would the water that did get down there actually be directed to the drain? Some moisture WILL get beneath the top of the tile, and to work properly, it MUST be directed to the drain via a sloped, waterproof layer. Anything else is just a hack.

    A linerless shower tends to start to smell like a swamp from the stagnant water accumulating there within the year. It also attracts carpenter ants and termites because the wood will get damp. Do you really want something like this in your house?

    Yes, some places recess the shower pan and literally let the water go into the soil beneath the shower. That may or may not prevent the wooden studs and curb from degenerating, but then, you have a big enticement for roots and insects to invade. Do it per industry standards (this assumes good workmanship) and you'll have a shower that will last until you decide to remodel, not fail prematurely.

    FWIW, rot resistant wood (i.e., pressure treated) isn't the answer, either. It tends to warp, sometimes considerably, as it dries out from treatment after installation. Tile hates movement.
     
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